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Bulletin (Tech.) 900
Fern
Enthracnose
A Guide for Effective Disease Management
J.O. Strandberg, R.H. Stamps, D.J. Norman
UNIVERSITY OF
WFLORIDA
Agricultural Experiment Station
Institute of Food and Agricultural Sciences
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Bulletin (Tech.) 900, Fern Anthracnose: A Guide for Effective Disease Management,
Copyright University of Florida 1997.
FERN ANTHRACNOSE: A GUIDE FOR
DISEASE MANAGEMENT
J. O. Strandberg, R. H. Stamps, and D. J. Norman1
p OF F LIBRARIES
NOTE: This publication contains research information on pesticides and pesticide use. Mention of a commercial or proprietary
product or chemical does not constitute a recommendation or warranty of the product by the author or the University of Florida,
Institute of Food and Agricultural Sciences, nor does it imply its approval to the exclusion of other products that may also be suitable.
Products should be used according to label instructions and safety equipment required on the label or by federal orstate law should
be employed. Users should avoid the use of chemicals under conditions that could lead to ground water contamination. Pesticide
registrations may change, so it is the responsibility of the user to ascertain if a pesticide is registered by the appropriate state
and federal agencies for an intended use.
'Professor (Plant Pathology), Professor (Environmental Horticulture), and Assistant Professor (Plant
Pathology), respectively, University of Florida, Institute of Food and Agricultural Sciences, Central Florida
Research and Education Center, 2807 Binion Road, Apopka, FL 32703.
G: -;.' i 0- L ,W UI A Lioi'ArAi 8
ACKNOWLEDGEMENT
Cover design and assistance with the illustrations by Mr. Chris Fooshee,
Coordinator, Research Services, University of Florida, Institute of Food and
Agricultural Sciences (IFAS), Central Florida Research and Education Center, is
gratefully acknowledged.
The authors also extend their sincere thanks to the following persons for advice
and suggestions as reviewers of the manual draft:
Dr. Wayne N. Dixon, Bureau Chief; Mr. Richard Gaskalla, Division Director; and
Dr. Tim Schubert, Plant Pathologist; of the Florida Department of Agriculture and
Consumer Services, Division of Plant Industry, Gainesville.
Drs. Monica Elliot and Gary Simone, University of Florida, IFAS, Fort Lauderdale
Research and Education Center and Department of Plant Pathology, respectively.
Mrs. Liz Felter, Extension Agent I; and Mrs. Linda Landrum, Extension Agent III;
University of Florida, IFAS, Cooperative Extension Service, Orange and Volusia
Counties, respectively.
Ms. Kathy Phillips, Office Manager; Mrs. Carolyn Pickles, Senior Clerk; Mrs.
Karen Stauderman, Biologist; and Ms. Rosemary Fowler, Lab Technician II;
University of Florida, IFAS, Central Florida Research and Education Center.
Special appreciation is also expressed to members of the Leatherleaf Fern
Anthracnose Task Force, to the Florida Fern Growers Association, and Mr. Earl
Ziebarth, State Representative, 26th District; for advice and support of our
research efforts.
Funding provided through The Florida Department of Agriculture and Consumer
Services, Division of Plant Industry has provided for the first printing of this
manual and has contributed significantly to the research projects that made this
manual possible.
TABLE OF CONTENTS
FERN ANTHRACNOSE: A GUIDE FOR DISEASE MANAGEMENT
TABLE OF CONTENTS
Section Subiect
1 INTRODUCTION
2 HOW TO USE THIS MANUAL
3 BIOLOGY OF THE FERN ANTHRACNOSE PATHOGEN
3.1 History, taxonomy, and origin
3.2 Biology of the fungus
3.2.1 Infection of fern leaves
3.2.2 Production of disease
3.2.3 Reproduction
3.2.4 Persistence and survival
3.2.5 Dispersal
4 BIOLOGY AND PRODUCTION OF LEATHERLEAF FERN
4.1 Origin, taxonomy, and use
4.1.1 Brief overview of production systems
4.2 Fern biology, growth, and development
4.2.1 Effects of temperature
4.2.2 Nutrient requirements
4.2.3 Moisture and irrigation
4.2.4 Freeze protection
5 THE FERN ANTHRACNOSE DISEASE
5.1 Impact and disease damage
5.2 Disease development and epidemics
5.3 Primary inoculum Sources and importance
5.3.1 Dispersal and reproduction of primary
inoculum
5.4 Reproduction and dispersal of secondary inoculum
5.5 Importance of water for disease development
5.6 Effects of temperature on disease development
5.7 Important interactions between host and pathogen
5.7.1 Susceptibility of leaves
5.7.2 Leaf initiation and development rates
5.8 Seasonal aspects of disease
6 TO AVOID OR MINIMIZE ANTHRACNOSE
6.1 Disease exclusion
6.2 Sanitation in ferneries
6.3 Workers and clothing
6.4 Decontamination of equipment with chemicals
6.5 Burning and mowing
6.6 Is Eradication feasible?
PAGE I
TABLE OF CONTENTS
7 FUNGICIDES FOR MANAGING ANTHRACNOSE
7.1 How fungicides suppress anthracnose
7.2 Where and when fungicides must be placed
7.3 Application methods
7.3.1 Low volume application methods
7.3.2 Chemigation
7.3.3 Special methods for rehabilitation
7.4 Application frequency of fungicides
7.5 Fungicide rates
7.6 Fungicide toxicity to leatherleaf fern
7.7 Fungicides and pathogen resistance
7.8 Fungicide programs for managing anthracnose
8 CULTURAL AND PRODUCTION METHODS TO MANAGE
ANTHRACNOSE
8.1 Avoiding local spread and promoting disease
8.2 Mowing and burning for rehabilitation
8.3 Minimizing irrigation frequency and wet foliage
8.4 Considerations for laborers and harvesting
8.5 Role of weeds and wild ferns
9 EVALUATING THE EFFECTIVENESS OF DISEASE
MANAGEMENT
9.1 Scouting for anthracnose
9.2 Sampling units and frequency
9.3 Basic approaches to sampling
9.4 Evaluation of sampled leaves
9.5 Records, summaries, and interpretation of results
9.6 Mapping disease foci
9.7 Integration with scouting for other pests
10 SEASONAL ASPECTS OF ANTHRACNOSE MANAGEMENT
10.1 Effect of fern growth
10.2 Seasonal requirements and management
throughout the year
10.3 Best times to rehabilitate damaged ferneries
11 DISEASE MANAGEMENT: OPPORTUNITIES AND
CHALLENGES
11.1 Understanding the problem
11.2 Obtaining the information you need
11.3 Implementing the program
11.4 Fern anthracnose and pesticide use
12 REFERENCES USEFUL FOR MANAGING FERN
ANTHRACNOSE
PAGE II
INTRODUCTION
1.0 INTRODUCTION
Infestation of a leatherleaf fern planting by the anthracnose fungus,
Colletotrichum acutatum, is a serious situation. At present, no simple
solution exists, and no single fungicide will control the disease. The
best approach is to prevent the introduction of the pathogen, but if
anthracnose is already present, it is still possible to prevent serious
losses and maintain profitable production by using appropriate
management practices. Successful management of any plant disease
requires a good understanding of the pathogen and the disease it
incites. Understanding fern anthracnose enables a systematic
approach to reducing its impacts on fern production. The purpose of
this manual is to provide a fundamental knowledge of fern anthracnose
and its relationship to leatherleaf fern production, as well as other key
information required to make effective disease management decisions.
PAGE 1 1
HOW TO USE THIS MANUAL
2.0 HOW TO USE THIS MANUAL
This manual is an educational and reference source. It summarizes
what is presently known about the anthracnose fungus and its
interactions with leatherleaf and other fern species, including the
impacts of disease on leatherleaf fern production. Some approaches
to avoiding the disease and methods for managing disease already
present, are outlined. The material reflects current knowledge, but will
need periodic revision. The loose-leaf format of the manual will
facilitate future revisions. We recommend that you read the entire
manual in order to fully understand fern anthracnose. Then the
manual will become a reference source that can be consulted when
making production or management decisions, or planning activities
likely to affect fern anthracnose. The material presented is organized
with these uses in mind.
PAGE 2 1
BIOLOGY OF THE PATHOGEN
3.0 BIOLOGY OF THE FERN ANTHRACNOSE PATHOGEN
3.1 History, Taxonomy, and Origin Leatherleaf fern anthracnose
first appeared in Florida ferneries in 1993. Severe damage and losses
occurred in some ferneries early in 1994. By June 1995, 42
companies (60%) that responded to our survey indicated that fern
anthracnose had been positively identified in their ferneries (Figure 1,
References 2 and 14). Since many of the infested ferneries were
spatially isolated, it is likely that the pathogen was spread simulta-
neously to several new locations within a few months. Therefore, fern
anthracnose should be regarded as easily-spread and fairly conta-
gious; this greatly complicates pathogen exclusion and disease
prevention. Presently (June, 1996), we estimate that one-third of the
land area devoted to leatherleaf fern production in Florida has been
infested. Although anthracnose has spread rapidly, and infested many
ferneries, it need not continue to do so; the pathogen can be excluded.
Interestingly, fern anthracnose has affected leatherleaf fern production
in Central America for many years. The pathogen now present in
Florida, a fungus, has been identified as a new pathotype of
Colletotrichum acutatum. Its origin, or how it may have been
introduced into Florida remain unknown. The term anthracnosee"
refers to a specific type of symptom or category of disease damage
described as ulcer-like or sunken lesions on leaves and stems.
Colletotrichum species, as a group, are known to produce such
symptoms.
,A 50
z 45
40 -
B 35 -
4 30
2 25
S 20-
10
X 5
1893 1994 1995
DATE OF FIRST OCCURRENCE
Figure 1. Incidence of fern anthracnose in Florida ferneries from its
apparent first appearance in 1993 through June, 1996.
PAGE 3 1
BIOLOGY OF THE PATHOGEN
To manage anthracnose, the biology
of the fungus must be understood
since it determines the pathogen's
ability to cause disease and survive
outside the leatherleaf fern leaf.
Pathogens such as Colletotrichum
acutatum have a special ability to
overcome the defenses of their hosts,
infect leaves, and incite disease.
Several species of cultivated and wild ferns can be infected and
damaged by the anthracnose pathogen. Thus far, in addition to
leatherleaf fern, fern anthracnose has severely damaged plantings of
holly fern (Cyrtomium falcatum) which is also grown for cut foliage in
Central Florida. The impacts of fern anthracnose on other cultivated
fern species, or the role of wild ferns in harboring or spreading the
anthracnose disease have not been fully determined (Reference 10).
3.2 Biology of the Fungus From the perspective of fern growers,
the most important biological properties of the pathogen determine its
ability to damage leaves; its maximum potential rate for disease
increase; how easily it can spread; how (and how long) it persists; and
how difficult it is to control. These properties are determined by the
life system, or biology, of the fungus. Life system refers to all
interactions between the pathogen, its host, and its environment. The
disease cycle of fern anthracnose (Figure 2) is only one aspect of the
pathogen's life system, but a very important one, because it describes
the economically important interactions with leatherleaf fern. The life
system is governed by the genetic makeup of the fungus which
ultimately determines its response to other organisms, to its
environment, and to activities of man. A basic knowledge of the life
system of C. acutatum makes it possible to manage the fungus and
the disease it incites. Once the life system of the fungus is
understood, what is needed to manage fern anthracnose becomes
fairly obvious, but how to go about it may not always be easy or
economical.
3.2.1 Infection of Fern Leaves Under favorable conditions,
spores of the pathogen can germinate within 2-4 hours. Germination
occurs wherever favorable conditions are encountered. Spores that
contact susceptible leaves form a germ tube (germination) within a few
hours after encountering favorable conditions of moisture and tempera-
ture (wet leaf surface and > 50 F*, [10 C]). On leaves, germ tubes
do not elongate very much but quickly form special structures that aid
in penetrating the leaf directly through the epidermis. Penetration and
infection occur very soon after germination.
3.2.2 Production of Disease Plants have natural defense systems
against infection and colonization by microorganisms. This explains
why most fungi and bacteria cannot cause disease on leatherleaf fern.
Pathogens such as Colletotrichum acutatum are exceptions: they have
a special ability to overcome the defenses of their hosts and incite
disease. With fern anthracnose, once infection has occurred, the main
defenses of the host have been overcome and the fungus colonizes
the young leaf tissue as a food source. Disease damage becomes
evident 3-4 days after infection. As infected leaves unfurl, expand,
PAGE 3-2
Figure 2. Disease cycle of fern anthracnose.
Lesions
-- Leaves become
infected
Fungicides prevent
only these processes
Spores germinate
and penetrate leaf
0 o 0
0
Spores contact
young leaves
0
0 o# o,
Abundant spores
produced in acervuli
on diseased leaves
\Leaf expands,
disease
progresses
D
Leaf
matures
damage
to fern leaf
PAGE 3 3
BIOLOGY OF THE PATHOGEN
Spores are easily spread
by tools, equipment,
people, or splashing,
flowing water
Mature leaves are
not very important
in the disease cycle
J
BIOLOGY OF THE PATHOGEN
.J
,
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Nt.
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Figure 3. Spores of Colletotrichum acutatum (mangification 200X).
Figure 4. Spore masses of Colletotrichum acutatum formed in
acervuli on diseased fern leaflets about five days after infection.
PAGE 3-4
BIOLOGY OF THE PATHOGEN
and grow upward through the fern canopy, colonized tissues are
destroyed and disease damage becomes obvious. Close inspection of
leaves in disease-damaged ferneries will reveal early infection sites
which are visible as tiny, brown, water-soaked lesions on newly-
infected leaves including those recently emerged from the soil. A
magnifying lens (10-20 X) is helpful to clearly see these sites. Only
young, immature, leaves are susceptible to infection and disease
damage; mature leaves, diseased or healthy, apparently play a small
role in the progress of disease (see Sections 4.2, 5.7.1, and Figure 2).
3.2.3 Reproduction Once the fungus has obtained adequate food
reserves from the colonized fern leaves, asexual reproduction follows.
A profusion of tiny spores are produced in acervuli (spore production
structures) that form on disease-damaged leaf tissue about 4-6 days
after infection (Figures 3 and 4). Spores are dispersed primarily by
water to other susceptible leaves (see Figure 2 and Section 3.2.1) and
the disease cycle is repeated (Reference 1). This cycle takes only 5-7
days under favorable conditions. A magnifying lens (10-20 X) is
helpful to clearly see the acervuli produced on disease-damaged
leaves and the pinkish-yellow spore masses that exude from them
(Figures 3 and 4). A microscope is needed to see individual spores
which are shaped like tiny grains of rice with one end slightly more
pointed than the other (Figure 3).
3.2.4 Persistence and Survival Spores washed from diseased
leaves may contact other susceptible leaves and, if conditions are
favorable, incite disease. If conditions are unfavorable for germination
and infection, even the spores deposited on susceptible leaves can die
within a few days from sunlight (ultraviolet radiation), desiccation, or
heat. Other spores become deposited on the soil or in plant debris;
their probable fate is not well known, but these spores do not persist
long in fernery soil or plant debris. For example, research has shown
that spores can survive 12 months in very dry soil or in dried, diseased
plant material, but such conditions are rare in Florida ferneries. Under
moist conditions more representative of fernery environments, spore
survival was reduced to 3-4 months. Many spores germinate without
contacting susceptible fern leaves; they apparently die quickly. As a
result, most spores are ineffective in perpetuating disease. Without
constant or periodic replacement, spore populations in soil and debris
decrease rather rapidly. All available evidence indicates that the
anthracnose fungus is unlikely to invade, live, or persist for long
periods in the soil, or to survive very long in the absence of the fern.
At present, asexual spores are believed to be the only stage of the
fungus that persists in soil and plant debris. Spores washed to the soil
or into plant debris, and fungal populations that persist in mature,
diseased fern leaves probably play little role in the natural spread or
Once the fungus has colonized the
fern leaf, asexual reproduction
follows. About 4-6 days after
infection, a profusion of tiny spores
are produced which are dispersed
primarily by water to other
susceptible leaves.
Spores produced by the fungus can
be easily spread by several means,
but these spores do not persist for
long periods in the soil or survive
very long in the absence of the fern.
PAGE 3-5
BIOLOGY OF THE PATHOGEN
Spores of Colletotrichum acutatum
can persist for up to 4 weeks on dry
clothing. This may explain the
introduction and rapid spread of fern
anthracnose.
If the number of spores being
produced on diseased leaves can be
greatly reduced, disease control
becomes much easier.
Spores of the fungus are more easily
spread under wet conditions.
Precautions to avoid spread must be
more stringent when wet conditions
prevail.
increase of fern anthracnose (Reference 1). However, spores that
reside on the soil or in plant litter can be spread by unusual weather
events such as flooding, or by human activity and eventually produce
disease (see Section 6).
Unfortunately, spores of Colletotrichum acutatum can persist for up to
4 weeks on dry clothing maintained at room temperature. This helps
to partially explain how the introduction and rapid spread of fern
anthracnose may have occurred because it is likely that fungal spores
can also persist for similar periods on tools, equipment and vehicles
(see Section 6).
Most spores are unsuccessful in producing new disease. If a large
enough proportion of spores are unsuccessful, fewer lesions (and new
spores) will be produced. If the incidence of new disease can be
prevented or reduced, spore populations on plants, in the soil, and in
plant debris will slowly decrease over time because the pathogen does
not persist well in ferneries. Accordingly, if most new leaf infections
can be prevented with fungicides, disease damage will decrease.
There will be fewer spores produced and populations of the fungus
and diseased leaves should decrease dramatically within a few
months. With fewer spores available to infect leaves, disease control
(both exclusion and protection) becomes much easier.
3.2.5 Dispersal Spores successful in infecting fern leaves initiate a
new cycle of disease. On disease-damaged tissue, millions of spores
are produced in structures called "acervuli" which quickly form about
the time that lesions become visible (see Figures 2, 3 and 4; Section
3.2.3). The spores are initially enveloped in a gelatinous matrix which
is water-soluble. When spore masses become wet with rain, dew, or
irrigation water, the matrix dissolves and the spores flow freely. In
water, spores disperse easily, and are washed on to new emerging
leaves, older susceptible leaves, or to the soil surface.
Under these same wet conditions, spores are more easily transferred
by contact because they adhere to dispersal vectors such as
equipment, vehicles, tools, and clothing. During wet conditions
produced by rain or irrigation, splashing, washing or flowing water and
surface runoff can effectively spread spores over moderate distances.
Clearly, water is critical for dispersal. This explains why disease
occurrence and intensity become much greater following frequent and
extended periods of wet weather. Although not yet verified, it is likely
that wind-blown rain or aerosol droplets can also spread anthracnose
spores since this occurs in similar diseases. Under dry conditions,
wind or any of the-above-mentioned factors are probably not efficient
in dispersal because the spores are much less mobile. When spores
are dry, they are probably not dispersed by wind; if present in water
droplets or aerosols formed by rain or irrigation, wind can spread them.
PAGE 3-6
BIOLOGY OF THE PATHOGEN
Pathogen exclusion and sanitation practices (Section 6) prevent the
introduction or uncontrolled dispersal and spread of C. acutatum
spores. The precautions discussed are designed to counteract or
avoid both natural spore dispersal and dispersal by man. When wet
conditions prevail, these precautions must be more stringent.
SUMMARY OF SECTION 3 BIOLOGY OF THE FERN
ANTHRACNOSE PATHOGEN
* Leatherleaf fern anthracnose appeared in Florida in 1993.
* 60% of the companies responding to our survey indicated that fern
anthracnose had been positively identified in their ferneries.
* The pathogen was spread simultaneously to several new locations
over a few months.
* Fern anthracnose is easily-spread and fairly contagious.
* Anthracnose has spread rapidly, but it need not continue to do so;
the pathogen can be excluded.
* The pathogen, a fungus, has been identified as a new pathotype of
Colletotrichum acutatum.
* The anthracnose pathogen can infect and damage several other wild
and cultivated fern species.
* Fern anthracnose has also caused economic losses in holly fern
(Cyrtomium falcatum) production.
* The fern anthracnose disease cycle is only one aspect of the
pathogen's life system.
* Once the biology of the fungus is understood, what is needed to
manage fern anthracnose becomes obvious.
* Under favorable conditions, spores of the pathogen can germinate
within 2-4 hours.
* Germ tubes do not elongate, but quickly penetrate the leaf directly
through the epidermis.
* Pathogens such as Colletotrichum acutatum have a special ability to
overcome the defenses of their hosts and incite disease.
* Only young, immature leaves are susceptible to infection and
disease damage; mature leaves, diseased or healthy, play little
role in the progress of disease.
* Once the fungus has obtained adequate food reserves from the
colonized fern leaves, asexual reproduction follows.
* Spores are produced on diseased tissue about 6 days after infection.
* Spores are dispersed primarily by water to other susceptible leaves.
* Spores persist in fernery soil or plant debris only 3-4 months.
* Without constant or periodic replacement, spore populations in soil
and debris decrease rather rapidly.
* The anthracnose fungus is unlikely to invade, live, or persist for long
periods in the soil or survive very long in the absence of the
fern.
PAGE 3-7
BIOLOGY OF THE PATHOGEN
* Asexual spores are believed to be the only stage of the fungus that
persists in soil and plant debris.
* Spores in the soil or plant litter can be spread by unusual weather
events such as flooding, or by human activity.
* Spores of Colletotrichum acutatum can persist for up to 4 weeks on
dry clothing maintained at room temperature.
* It is likely that fungal spores can also persist for similar periods on
tools, equipment and vehicles.
* If the incidence of new disease can be prevented or reduced, spore
populations on plants, in the soil, and in plant debris will slowly
decrease over time.
* If most new leaf infections are prevented with fungicides, disease
damage will decrease, fewer spores will be produced, and
disease control becomes much easier.
* Spores are produced in a water soluble matrix; when wet with rain,
dew, or irrigation water, the matrix dissolves and the spores
flow freely.
* Under wet conditions, spores are more easily transferred by
equipment, vehicles, tools, and clothing.
* Rain or irrigation water can also spread spores in washing or flowing
water, and in surface runoff.
* Under dry conditions, wind or any of the-above-mentioned factors
are not efficient in dispersal because the spores are much less
mobile.
* Disease prevention measures must be more stringent when wet
conditions prevail.
PAGE 3-8
BIOLOGY AND PRODUCTION OF FERNS
4.0 BIOLOGY AND PRODUCTION OF LEATHERLEAF FERN
To manage fern anthracnose, the biology and production of leatherleaf
fern must be considered because the life system of a pathogen such
as C. acutatum is closely tied to the biology of its host, and because
disease damage is produced through complex interactions between the
host and pathogen. Fern production systems must also be considered
because they help to determine the environment that allows the two
species to interact so vigorously. Environments created by production
systems are affected by weather and the activities of man. Little can
be done about weather, but most human activities involved in fern
production can be managed to the detriment of fern anthracnose.
4.1 Origin, Taxonomy, and Use Leatherleaf fern (Rumohra
adiantiformis) is a true fern native (with some exceptions) in many
subtropical and tropical climates throughout the world. Leatherleaf fern
is a creeping, herbaceous perennial. Almost all leatherleaf fern grown
for cut foliage is propagated vegetatively, but the origin of presently-
cultured plant material is unclear. Leatherleaf fern leaves (frond is a
term also used and refers to a finely-divided leaf) are used in floral
arrangements and must be essentially blemish-free to be commercially
acceptable. A significant proportion (-25%) of the cut fronds are
exported to world-wide markets. Interestingly, leatherleaf fern is not
native to Central America (References 8 and 14), where leatherleaf
fern production has been plagued by anthracnose for many years.
4.1.1 Brief Overview of Production Systems In Florida,
leatherleaf fern is grown on approximately 7,000 acres [2,860 ha] and
has an estimated annual wholesale value of over $70 million. Because
of value and demand, this fern is now being produced in many parts of
the world. In Florida, it is grown under approximately 70% shade,
predominantly on well-drained, sandy soils with low water- and
nutrient-holding capacities. About two-thirds of the production is
artificially shaded with polypropylene shade fabric; the remainder is
naturally shaded by trees, mostly evergreen oaks (Quercus spp.). Due
to inadequate rainfall during certain periods of the year, and the need
to cold-protect the crop with water during freezes, supplemental
irrigation is required for commercial production. Irrigation water,
fertilizers, and pesticides are generally applied using solid-set overhead
impact sprinkler irrigation (References 5 and 8).
Mature, dark-green fronds are harvested by hand (using clippers) and
rubber-banded together in bunches of 20 to 25 fronds. The bunches
are taken to packing sheds where they are processed, packed in
corrugated fiberboard cartons, and cooled to -4 C [400 F] until
shipped. Fronds are grown and harvested all year; therefore,
conditions favorable for anthracnose (abundant immature leaves,
irrigation, and harvesting activities) occur throughout the year.
The biology of leatherleaf fern and
environment provided by fern
production systems are important in
managing anthracnose and their
effects should be understood.
PAGE 4- 1
BIOLOGY AND PRODUCTION OF FERNS
The biology of leatherleaf fern is
uncomplicated as it relates to cut
foliage production.
Fern leaves are produced throughout
the year and the anthracnose fungus
remains active throughout the year as
well.
Growth and development of
leatherleaf fern leaves have been
divided into seven convenient growth
stages.
4.2 Fern Biology, Growth, and Development The biology of
leatherleaf fern as it pertains to cut foliage production is relatively
uncomplicated. Since leatherleaf fern is vegetatively propagated, its
life cycle is of little concern here, but additional information on its
biology may be found in Reference 14. There is little phenotypic
variability in clones now being produced. All types of leatherleaf are
similar in growth habit and development; all are susceptible to
anthracnose. However, other species of fern attacked by anthracnose
differ greatly in susceptibility (Reference 10). In leatherleaf fern, new
leaves are produced periodically from underground rhizomes (Figure
5). Initiation and development rates of new leaves are of great
importance because the new leaves interact most strongly with the
pathogen. Without a continuous supply of new leaves in susceptible
growth stages, rapid disease progress cannot be maintained.
New fern leaves are initiated throughout the year (Reference 3,
Section 4.2.1), but initiation rates and developmental periods vary
greatly depending upon the season and condition of the fern plant. In
general, more new leaves are initiated in the early fall and spring
because initiation rate is related to temperature (Reference 3). The
time required for leaves to develop to maturity (Growth Stage 7, see
Figure 6) is also variable and ranges from 7-21 days depending on the
season (Authors, unpublished data).
Growth and development of leatherleaf fern leaves have been
categorized into seven stages. These stages are useful for pest
damage assessment, understanding and describing stages of leaf
development, and for categorizing leaf stages susceptible to the
anthracnose pathogen. The seven stages are:
Growth Stage 1 Crozier circinatee) or fiddlehead stage.
Recently emerged from soil. Entire leaf tightly-curled, not
expanded, hairy (scale-covered), silvery-green to very light
green.
Growth Stage 2 Leaf beginning to uncurl, rachis straight or
nearly so. Leaflets remain unfurled, pale to light green.
Growth Stage 3 Early Expanding. Most leaflets remain tightly
curled, but some leaflets have expanded, and the leaf is
beginning to enlarge.
Growth Stage 4 Mid Expanding. About half the leaflets
(mostly the apical) remain furled to varying degrees. The other
half are unfurled, and the leaf is expanding rapidly.
Growth Stage 5 Late Expanding. Most leaflets now
unfurled. The leaf is mostly expanded and has nearly reached
its final size. Only some of the leaflet tips remain unfurled.
PAGE 4-2
BIOLOGY AND PRODUCTION OF FERNS
Pinna
(primary
division of
the frond),
Pinnule
(secondary
division of
the frond)
Crozier or fiddlehead
(emerging frond)
Leaf bud
Terminal bud
I .< d
Roots
Figure 5. Growth habit of leatherleaf fern
PAGE 4 3
Mature
frond
(leaf)
Immature fronds
(leaves)
BIOLOGY AND PRODUCTION OF FERNS
Growth Growth Growth Growth
Stage 1 Stage 2 Stage 3 Stage 4
Growth Growth Growth
Stage 5 Stage 6 Stage 7
Figure 6. Important growth and development stages of leatherleaf fern leaves
PAGE 4 4
BIOLOGY AND PRODUCTION OF FERNS
Growth Stage 6 Fully expanded. Leaf remains light to pale
green, thin and filmy not leathery. At this stage, the leaf is
no longer susceptible to infection.
Growth Stage 7 Mature. Leaf fully expanded, dark green and
leathery texture. No longer susceptible to infection.
The seven growth stages are illustrated in Figure 6 which can also be
used as a key for classifying leaves into growth stages.
Important Note Leaves in Growth Stages 1 5 are susceptible to
infection by the anthracnose fungus. Those in Growth Stages 6 and 7
are no longer susceptible. A healthy leaf reaching Growth Stage 6 will
not become diseased. This is the reason that when scouting fern for
anthracnose, leaves in Growth Stage 5 or 6 are the sampling unit of
choice (Section 9).
4.2.1 Effects of Temperature Leatherleaf fern fronds develop
faster at higher temperatures, but the condition and food reserves of
the fern plant also affect initiation and development rates. Leaves that
emerge in the spring and summer usually reach Growth Stage 6 (early
maturity, no longer susceptible) more quickly than leaves initiated
during other seasons. Frond vase life also decreases as leaf growth
and development rates increase (Reference 3). New leaves are the
susceptible units needed to perpetuate disease (Sections 3.2.1 and
5.2 through 5.7), and temperature greatly influences the availability of
new leaves and the rate at which they appear. Therefore, seasonal
temperatures also affect disease progress rates and indirectly
determine optimum fungicide application intervals. This is one of the
main reasons that disease management and fungicide programs must
change with the season of the year (Section 10).
4.2.2 Nutrient requirements Nutrient requirements for leatherleaf
fern are discussed extensively in Reference 5. Primary nutrient
sources include the soil, irrigation water, pesticides (which provide
mainly micronutrients) and fertilizer. Growers can significantly affect
the two major avenues of nutrient losses leaching and removal due
to harvesting of the crop. Leaching losses, in particular, can be
reduced by carefully timing fertilizer applications, selection of slow-
release nutrient sources, applying nutrients in small amounts, and by
practicing proper irrigation system management (Reference 5, Sections
4.2.3 and 8.1). There is no evidence that nutrient levels directly affect
fern anthracnose.
4.2.3 Moisture and irrigation Irrigation requirements for leatherleaf
fern are also discussed in Reference 5. Leatherleaf fern does not
Leaves which reach Growth Stages 6
and 7 without becoming diseased are
no longer susceptible to infection by
anthracnose.
Nutrient levels do not normally affect
anthracnose.
PAGE 4- 5
BIOLOGY AND PRODUCTION OF FERNS
Irrigation requirements for fern
production and the effects of irrigation
on anthracnose must be understood.
Irrigation events should be planned to
minimize anthracnose development.
Freezing has little effect on fern
anthracnose, but the large volumes of
water used in freeze protection can
spread the spores of the anthracnose
fungus.
require a great deal of water. Only about 20 inches of water per year
are taken up by the roots and transpired from the leaves. The reason
for this relatively low water use is that the crop is grown under heavy
shade which reduces solar radiation that reaches the leaves and
thereby lowers transpiration rates. With normal expected rainfall,
relatively little irrigation is necessary to produce leatherleaf fern,
especially during the rainy season (June-October). During the
summer, many growers significantly reduce the frequency of watering
and the amount applied to try to minimize fern growth and thereby
maximize frond quality and vase life (References 3 and 5, Section
4.2.1).
For many reasons, ferns should be irrigated only when necessary. In
general, the more irrigation water applied to the crop, the more often
the foliage will remain wet. Prolonged leaf wetness periods are
conducive to disease development and are essential for spore
germination and dispersal (Sections 3, 5, and 8). Excessive irrigation
also erodes protective fungicides from susceptible foliage. Frequency
and duration of irrigation events should be based upon estimated,
measured, or calculated soil moisture conditions and not on a
calendar-based schedule.
4.2.4 Freeze Protection During prolonged freeze protection events,
soils are likely to become saturated with water. Runoff water that
results from irrigation and melting ice can wash spores into previously
uninfested areas of ferneries. Although spore concentrations in runoff
water are likely to be low, the spores can be spread and infect other
plants or nearby ferneries and result in new infestations (see Section
5.4.2). Contamination of water recovery ponds is also possible.
However, most water entering these ponds is filtered by the soil.
When surface runoff enters the pond directly, the dilution of the spores
would probably be great enough as to render irrigation water drawn
from the pond non-infective. However, little is known about this aspect
of anthracnose or the potential for spore dispersal through irrigation
water obtained from holding ponds located near diseased ferneries.
Irrigation for cold protection is covered briefly in References 5 and 6.
Freezing, (or freeze protection) by itself, has little influence on the
anthracnose disease.
SUMMARY OF SECTION 4 BIOLOGY AND PRODUCTION OF
LEATHERLEAF FERN
* The life system of Colletotrichum acutatum is closely tied to the
biology of leatherleaf fern.
* Fern production systems greatly influence anthracnose incidence
and development.
PAGE 4-6
BIOLOGY AND PRODUCTION OF FERNS
* Leatherleaf fern is now produced in many parts of the world.
* In regard to cut foliage production, the biology of leatherleaf fern is
relatively uncomplicated.
* There is little phenotypic variability in types of leatherleaf fern now
being grown; all are equally susceptible to anthracnose.
* Initiation and development rates of new leaves are of great
importance to anthracnose development.
* Leaf initiation and development rates vary greatly with the season
and condition of the fern plant.
* The time required for leaves to mature is variable and ranges from
7-21 days depending upon the season.
* Growth and development of leatherleaf fern leaves have been
categorized into seven stages useful for pest management.
* Leaves in Growth Stages 1 through 5 are susceptible to infection by
the anthracnose fungus; those in Growth Stages 6 and 7 are
no longer susceptible.
* Frond vase life decreases as leaf growth and development rates
increase.
* Seasonal temperatures affect disease progress rates and determine
optimum fungicide application intervals.
* Nutrient levels probably do not affect fern anthracnose.
* Leatherleaf fern should be irrigated only when necessary.
* Prolonged leaf wetness periods are conducive to disease
development.
* Little is known about the potential for spore dispersal through
irrigation water.
* Freezing has little influence on the anthracnose fungus.
* Large amounts of water used in freeze protection can effectively
spread the spores of the pathogen.
PAGE 4-7
THE FERN ANTHRACNOSE DISEASE
5.0 THE FERN ANTHRACNOSE DISEASE
Anthracnose is the result of interactions between the fungus,
Colletotrichum acutatum, and the fern plant. The most important of
these, infection and colonization of fern leaves, result in economic
damage to the harvested product the fern frond. Disease impacts
the fern in other ways. Yield, and growth and development rates are
probably also affected, but our methods are not sensitive enough to
detect these effects, nor has detailed research documented them. This
section discusses impacts of anthracnose on fern production and how
interactions with the fern and its culture affect the pathogen in regard
to disease epidemics and disease development. Economic losses and
costs associated with control are also important impacts to the grower;
we will not discuss them here, but acknowledge that to minimize them
is a major goal. Familiarity with these impacts is needed to understand
the management approaches proposed in Sections 6 through 10.
5.1 Impact and Disease Damage Anthracnose impacts fern
production by causing unsightly disease damage that renders the
fronds unsalable. Only immature leaves can be infected by the fungus.
Mature leaves, even when diseased, are of somewhat less importance
in the development and progress of disease epidemics. However,
damage is more obvious on older leaves and becomes more so as the
leaf unfurls and matures into an unsalable product. On immature
leaves, the actual amount of leaf tissue colonized by the fungus
appears small, but the damaged tissues are at an embryonic stage.
The true extent of damage becomes apparent as the leaf matures. As
the leaf expands, disease-damaged areas become larger and turn
dark-brown to black as the affected tissue dies and dries out.
Disease damage on mature leaves is more conspicuous because some
affected leaflets and leaf areas are missing; their growth and develop-
ment has been disrupted or curtailed by disease damage that occurred
when the tissues were immature. Such leaves are often severely
deformed; they expand or develop asymmetrically due to damaged, or
missing leaflets. Inspection of young, newly-infected leaves (including
Growth Stage 1 and 2) will reveal tiny, brownish, water-soaked areas
particularly (but not exclusively) on the margins of infected leaflets.
This clearly demonstrates that early infection and disease damage are
initiated days or even weeks before it becomes obvious. These small,
obscure lesions are the sites where disease is initiated. The purpose
of fungicide applications is to protect leaves and prevent this stage of
disease from occurring.
Disease damage on mature leaves does not progress further.
Although the fungus can be recovered from these tissues by special
isolation techniques, it is mostly in a dormant state, and does not
sporulate heavily, nor further damage mature leaves. Thus, fungicides
The fern anthracnose disease is
initiated by the infection of very
young leaves, but damage becomes
more obvious as the leaves mature.
Infection of young leaves occurs days
or even weeks before disease
damage becomes obvious.
The purpose of fungicide applications
is to protect leaves and prevent
disease from occurring.
PAGE 5- 1
THE FERN ANTHRACNOSE DISEASE
Disease visible on mature leaves
does not progress further. Mature
leaves are not very important in
disease epidemics and fungicides
have no effect on this stage of
anthracnose.
Many factors affect anthracnose
development, but the most important
are temperature and moisture.
Anthracnose does not appear
suddenly. It develops over a period
of a few weeks or more before it
becomes obvious to the casual
observer.
have little or no effect on this stage of the disease. For these reasons,
mature leaves, even if diseased, play no significant role in the
development and progress of disease epidemics. In badly-infested
plantings, or foci of disease (hot spots), which have experienced
prolonged conditions conducive to disease (for example, rains in
summer, inadequate fungicide applications), almost all new leaves
sustain severe damage. Few immature, pale-green leaves (Growth
Stage 5 and 6) are apparent here because they have been devastated
by anthracnose. Over the long term, the vigor of these plants will be
significantly reduced; whereas the primary short-term impact to
production is cosmetic damage to leaves which would have become
the harvested product.
5.2 Disease Development and Epidemics Contrary to popular
belief, fern anthracnose epidemics do not develop overnight or come
from nowhere; they result from increases in populations of the fungus
and diseased leaves and plants over time (weeks). The increase of
disease with time may also be thought of as the progress of an
epidemic or "disease progress". Apparent rates of disease
development and progress of epidemics are determined by several
factors. Among the most important are environmental factors, both
local climate and weather, which greatly affect pathogen growth,
development, reproduction, and dispersal. Other factors act to limit
the maximum potential rate of disease increase; these factors are
relatively fixed and are determined by the life system and genetic
makeup of the fungus. Still other factors more closely related to the
host also affect the progress of epidemics. Among these are leaf
initiation rate, leaf development rate (to maturity), host susceptibility,
response of host (and pathogen) to cultural methods, and activities
associated with growing and harvesting ferns. Though many of the
above-mentioned factors cannot be manipulated to the detriment of
anthracnose, many opportunities exist for avoiding disease or slowing
the progress of epidemics. Examples are modification of cultural
methods and harvesting activities and appropriate fungicide programs.
Epidemics begin with an initial infection of one or more plants, followed
by reproduction and dispersal of the pathogen (in the form of spores).
This results in additional infection sites, and the process is repeated.
The initial infection (assuming a healthy fern planting) is caused by
introduced spores which are called the primary inoculum. The source
and amount of primary inoculum are important.
5.3 Primary Inoculum Sources and Importance It is important
to understand potential sources of primary inoculum and the relative
quantities of spores expected from them. Disease prevention
strategies (Section 6) are based upon exclusion or reduction of
comparatively small amounts of primary inoculum. Preventative
PAGE 5 2
THE FERN ANTHRACNOSE DISEASE
sprays, on the other hand, are designed to suppress disease already
present by counteracting the enormous amounts of spores that are
produced when anthracnose becomes established. The concept of
primary inoculum is also important in understanding the time interval
between the introduction of the pathogen and the time when disease
damage becomes extensive enough to be noticed.
In theory, a single spore can result in an infection, but research has
shown that about 100 spores of C. acutatum are required to achieve
an infection. However, 100 is a relatively small number in relation to
the number of spores which can be produced on a single, diseased
fern leaflet. When opportunities for introduction of primary inoculum
occur, an adequate number of spores to infect the plant on which they
are deposited is likely to be provided. Accordingly, large quantities of
primary inoculum will generally result in more initial disease which, in
turn, will result in more disease damage over a given time interval and
a greater apparent rate of disease increase. However, even a
relatively small amount of primary inoculum, given enough time, will
result in a serious disease epidemic. It just takes longer.
Other diseased fern plantings (not necessarily nearby) are potential
sources of primary inoculum. Wild ferns, though some are susceptible
to anthracnose, do not appear to be important sources. Among
cultivated ferns, only diseased holly fern, Cyrtomium falcatum, has
been documented as a potential source of primary inoculum.
Conversely, infected leatherleaf fern can serve as a source of inoculum
for other cultivated and wild fern species.
As already mentioned, spores produced on diseased fern can be
transferred to healthy fern by clothing and equipment, particularly when
leaves are wet. The number of spores introduced by these processes
tends to be small, but the spores can be transported over large
distances. Small numbers of spores tend to initiate small amounts of
disease because the probability of a particular spore infecting a plant
and establishing disease is also small. The probability of infection
increases as the number of introduced spores increases. If there are
few initial infections, particularly when isolated or scattered, it will take
some time for disease to increase to levels where it becomes obvious.
In most infested ferneries, initial reports of anthracnose are almost
always confined to small, isolated foci. These are likely a result of the
successful introduction of small amounts of primary inoculum.
For example, vehicles and equipment can transfer more inoculum than
a single contaminated tool or worker, but an entire crew of workers can
transfer small amounts of primary inoculum to multiple sites within a
fernery via clothing, containers, and hand tools; the effect will be the
same as if much larger amounts of inoculum had been introduced.
Primary inoculum is commonly
introduced into ferneries by the
transport of fungus spores on
vehicles, tools, equipment, or
workers' clothing.
PAGE 5 3
THE FERN ANTHRACNOSE DISEASE
Once disease is introduced into a
fernery, tremendous numbers of
spores are produced daily on
diseased foliage. At this point, an
appropriate fungicide program is
required to protect new leaves from
infection.
Significant disease development will become apparent much earlier
than if a small amount of primary inoculum was introduced in a single
location. Surface water runoff from infected areas can transfer large
numbers of spores to multiple sites in nearby ferneries. Other vectors
such as animals, insects, or wind-blown leaves and soil are thought to
be relatively unimportant compared with the activities of man in
introducing and dispersing primary inoculum.
The concept of primary inoculum is important for understanding
disease prevention and pathogen exclusion strategies (Section 6).
Sanitation, and particularly exclusion, may not be particularly efficient,
but because of the relatively small number of spores involved (primary
inoculum), they can be very effective. Concepts of primary and
secondary inoculum may seem to be overly dependent upon your point
of view, but they are important in managing anthracnose and
understanding how a fernery can become infested in the first place.
5.3.1 Dispersal and Reproduction of Primary Inoculum The
quantity of primary inoculum that is introduced partially determines the
initial level of disease and the apparent rate of disease increase that
results from its introduction (Section 5.3). The source and method of
spread usually determine the relative quantity of spores introduced.
Once initial disease is established, reproduction of the pathogen
creates additional inoculum that contributes to disease development
and spread within the new location. These spores are known as
secondary inoculum. The same vectors that disperse primary
inoculum are also important in spreading secondary inoculum
(Sections 5.3.1, 5.4 and 6).
5.4 Reproduction and Dispersal of Secondary Inoculum There
are important differences between primary and secondary inoculum.
For example, spores produced from secondary (on-site) infections are
produced in great quantities for several days. These spores need only
be dispersed by water over small distances to encounter other
susceptible fern leaves. Moreover, they are dispersed under
conditions ideal for infection of new leaves and need not suffer
desiccation, aging, or exposure to UV light. No vectors other than
water or those provided by normal cultural activities are required to
disperse them (see Sections 3.2.5 and 6). These dispersal processes
are much more efficient than many of those discussed in Section 5.3.
Thus, spores produced as secondary inoculum are likely to be more
numerous and effective. Once secondary inoculum is present,
sanitation becomes less effective (but still useful); disease exclusion is
no longer an option. At this point, effective chemical control strategies
are required. However, it is still possible (and useful) to reduce rates
of spread and to supplement chemical controls with appropriate
cultural disease management tactics discussed in Sections 6 and 8.
PAGE 5-4
THE FERN ANTHRACNOSE DISEASE
5.5 Importance of Water For Disease Development In addition to
its role in spore dispersal, water plays a critical role in other aspects of
disease development. Free water, present as a thin film or as droplets
on the leaf surface, is essential for spore germination, infection of
leaves, colonization of the leaf tissues, and for producing new spores.
In controlled-environment experiments, incidence and severity of
anthracnose damage increased directly with the interval that fern
leaves remained wet each day. Wet periods must coincide with
disease-favorable temperatures. Thus, disease is more likely to be
severe following rainy periods in summer or when frequent dew
produces extended leaf wetness intervals. Cultural practices that
reduce leaf wetness periods are advantageous. They reduce chances
for infection and opportunities for spore dissemination, and disease
development is slowed.
Unfortunately, spore germination and infection take place very quickly
- within 2-3 hours at 220 C [720 F], so there are few opportunities to
completely avoid infection by minimizing the duration of leaf wetness.
Leaf wetness periods of 2-4 hours duration are common in ferneries.
They are subject to weather (for example dew) and therefore relatively
uncontrollable. Little can be done to avoid them, but growers can
avoid creating additional wet periods or prolonging natural wet periods
by irrigating.
5.6 Effects of Temperature on Disease Development The fern
anthracnose fungus can infect and produce disease damage when
temperatures remain above approximately 160 C [500 F]. Low
temperatures (including those below freezing) do not normally affect
anthracnose except to temporarily slow disease development rates.
Temperatures high enough to significantly affect anthracnose are not
normally encountered in Florida. Although life processes of the
pathogen are greatly slowed at low or freezing temperatures, they
quickly resume when temperatures again become favorable. Air
temperature is most important at night since the leaves are likely to be
wet during this period, but daytime temperature is also important,
especially when the foliage remains wet for prolonged periods.
Disease-favorable air temperatures when leaves are dry also benefit
disease development, but not as much as when leaves are wet. Under
moist conditions, the warmer the temperature, the faster disease will
progress. Clearly, Florida summers greatly complicate the
management of fern anthracnose. The anthracnose fungus is a very
effective pathogen. Temperatures favorable for its life system should
be quite similar to those for fern. This is the case, except that the
fungus survives freezing very well and the fern does not.
5.7 Important Interactions Between Host and Pathogen The
most important of these results in disease damage. Knowing how this
Water is essential in all phases of
fern anthracnose. Abundant water
and prolonged leaf wetness periods
accelerate the development and
spread of fern anthracnose.
Temperature affects fern growth and
development as well as reproduction
of the anthracnose fungus. The
combined effects of temperature on
host and pathogen are the most
important factors that affect
anthracnose, if water is not limiting.
PAGE 5-5
THE FERN ANTHRACNOSE DISEASE
Interactions between the pathogen
and the fern result in disease damage
as the fungus infects the fern leaf and
colonizes it as a food source.
Only immature leaves are susceptible
to infection; mature leaves, if healthy,
will be unaffected. If anthracnose is
present, fungicides are needed to
protect young leaves during the
period when they are susceptible to
infection.
occurs is essential for managing anthracnose. The anthracnose
fungus has a special ability to infect and colonize the fern leaf as a
food source. In regard to the fern, the main advantage of the
pathogen over non-pathogenic fungi is its ability to overcome the
defenses of the fern leaf and utilize it as a food source before other
microorganisms can. Eventually, other fungi and bacteria also invade
and colonize disease-killed portions of fern leaves; they soon provide
severe competition for the pathogen. When this occurs, disease
development slows and the pathogen is apparently able to persist only
in a relatively inactive state in diseased tissue. This may be the main
reason that significant reproduction and disease development ceases
in mature, diseased leaves, and why these leaves no longer play an
important role in disease progress.
Disease damage results directly from the colonization of leaf tissue by
the pathogen. Once the leaf is penetrated, cells are killed in advance
(possibly by toxins) of the filamentous mycelia as they grow through
the leaf tissues, colonizing it as a food source. Eventually, portions of
the vascular system or water-conducting cells are also killed. Then,
large areas of the leaves, deprived of water, die rapidly. This results
in the dark, scorched appearance characteristic of the disease.
During early stages of colonization, the fungus begins to reproduce.
Numerous spores are formed in acervuli (see Section 3.2.3, Figures 2
and 4) produced in abundance on newly-colonized leaf tissue.
Sporulation commences within 3-4 days after infection, or about the
time early disease damage is evident, and continues for about a week
or more. It is particularly important to note that these processes occur
almost continuously on numerous leaves and leaflets throughout the
population of diseased plants. New leaves and plants are becoming
infected and many additional spores are being produced every day.
This greatly complicates chemical control strategies.
5.7.1 Susceptibility of Leaves Experiments have demonstrated
that only young leaves and leaf tissue are susceptible to infection and
disease damage. Mature leaves can be penetrated by the fungus, but
significant colonization, disease damage, and reproduction do not
occur. Young, susceptible fern leaf tissue can be infected and develop
disease damage until it is completely expanded and unfurled, yet still
not fully mature (Growth Stage 5 see Figure 6 and Section 4.2). On
leaves in Growth Stages 3 through 5, not all of the tissues are
susceptible; it is primarily the immature, unfurled leaflets and leaflet
tips which are susceptible to infection and disease damage. These
tissues are the most difficult to protect with fungicides since they are
tightly curled and rapidly-expanding. Leaves may be infected at any
time after they emerge from the soil, while they unfurl, expand, grow
upward, and finally begin to mature.
PAGE 5-6
THE FERN ANTHRACNOSE DISEASE
When anthracnose is present, these leaves must be protected by
fungicides during the critical period from initiation through development
to Growth Stage 5. Such leaves require protection lasting from several
days to 2 weeks depending on development rates. Leaves that reach
Growth Stage 6 without visible disease damage will remain unaffected
by anthracnose.
5.7.2 Leaf Initiation and Development Rates Development of
anthracnose epidemics depends upon a supply of new leaves. Higher
leaf initiation rates allow greater rates of disease progress. Leaf
initiation and development rates vary according to temperature and the
condition of the fern plant (Reference 5, Section 4.2). A fern plant
initiates a new leaf about every five to eight days, but this interval
varies greatly. New leaves can require 7-21 days to reach Growth
Stage 6 (no longer susceptible to infection). Protection of leaves
during their development through Growth Stage 5 is essential.
Unfortunately, leaf initiation and development is not a synchronous
process. In a fern planting, there are a myriad of leaves in all growth
stages and susceptible leaf tissue is appearing continuously. This is
the main reason that fungicides applied at 7-day intervals are
ineffective during much of the year and why shorter application
intervals are required. Fungicides applied at shorter intervals can
protect more new leaves and leaf tissue from infection. During periods
with high leaf initiation rates, special efforts to protect as many new
leaves as possible from infection are required (Section 7.4).
5.8 Seasonal Aspects of Disease Temperature, moisture, and leaf
initiation and development rates all combine to influence seasonal
changes in the progress of anthracnose epidemics. The pathogen
remains active throughout the year because, on the average, disease
favorable conditions prevail year-round in Florida ferneries. However,
relative levels of disease intensity and rates of disease progress will
decrease noticeably during prolonged periods of low night tempera-
tures, slow rates of leaf initiation and fern growth, and in dry periods.
These weather-related factors account for the seasonal nature of fern
anthracnose. During periods that are relatively unfavorable for
disease, disease progress is slowed, and fewer new leaves, infected
leaves, and fungus spores are being produced, so it is much easier to
suppress anthracnose. The intensity of fungicide programs can be
adjusted to reflect these periods. For example, with presently available
fungicides, it can be very difficult to maintain disease at acceptably low
levels during the summer, even with intensive fungicide programs
(Sections 7.1 through 7.8). It is much easier to gain control of disease
during the fall and winter when weather is more unfavorable for
disease (Section 10).
A continuous supply of young,
susceptible leaves is needed for
anthracnose to continue to develop at
maximum rates. A reduction in leaf
initiation rate limits the progress of
anthracnose.
Seasonal changes in average
temperature and abundance of
moisture greatly influence
anthracnose development,
particularly in fall and winter.
PAGE 5-7
SUMMARY OF SECTION 5 THE FERN ANTHRACNOSE DISEASE
* Infection and colonization of fern leaves by the fungus result in
anthracnose damage.
* Disease damage is more obvious on older leaves.
* At new infection sites on immature leaves, the amount of damaged
leaf tissue appears small, but the tissues are embryonic.
* The true extent of damage becomes apparent as the leaf matures.
* Early infection and disease damage are initiated long before they
become obvious to the casual observer.
* Fungicide applications can protect leaves from infection and thereby
prevent disease damage from occurring.
* Disease damage seen on mature leaves does not progress further,
so fungicides have little or no effect at this stage.
* Fern anthracnose epidemics do not develop overnight or come from
nowhere; they result from increases in populations of the
fungus and diseased plants over time (several weeks).
* Weather greatly affects pathogen growth, development,
reproduction, and dispersal.
* Other factors important to anthracnose epidemics are fern leaf
initiation and development rates and cultural activities
associated with growing and harvesting fern.
* Epidemics begin with infection of one or more plants, followed by
spore production and dispersal of the pathogen.
* Initial infections are caused by introduced spores called the primary
inoculum.
* Sources and amounts of primary inoculum (spores) are important.
* Large quantities of primary inoculum result in greater amounts of
disease.
* Disease prevention relies upon exclusion or reduction of
comparatively small amounts of inoculum.
* Wild ferns do not appear to be important sources of inoculum.
* In addition to leatherleaf, only holly fern has been seriously
damaged by fern anthracnose.
Spores can be transferred to healthy fern by contaminated clothing
and equipment, particularly when leaves are wet.
Numbers of spores introduced by these processes tend to be small,
but can they can be transported over large distances.
Initial introductions of anthracnose are almost always confined to
small, isolated foci.
Surface water runoff from infected ferneries can transfer large
numbers of spores to nearby ferneries.
Animals, insects, or wind-blown leaves and soil are thought to be
relatively unimportant in spreading anthracnose.
Once introduced, reproduction of the pathogen creates additional
inoculum that contributes to disease development and spread
within the new location. These spores are known as
secondary inoculum.
PAGE 5-8
THE FERN ANTHRACNOSE DISEASE
THE FERN ANTHRACNOSE DISEASE
* Secondary inoculum is dispersed by water over small distances
under conditions ideal for infection of new leaves.
Fungicide sprays are designed to counteract the enormous numbers
of spores that are produced on diseased leaves.
It is possible to reduce the rate of disease spread with good
management practices.
Water plays a critical role in disease development.
The fern anthracnose fungus can infect and produce disease
damage when temperatures remain above 50 F.
Low temperatures (including those below freezing) temporarily slow
disease development which resumes when temperatures again
become favorable.
Under moist conditions, the warmer the temperature, the faster
disease will progress.
* The main advantage of the pathogen over non-pathogenic fungi is its
ability to overcome the defenses of the fern leaf and utilize it
as a food source before other microorganisms can do so.
* Disease damage results directly from the colonization of leaf tissue
by the fungus as a food source.
* Sporulation commences within 3-4 days after infection, or about the
time early disease damage is evident.
* Only young leaves and leaf tissue are susceptible, mature leaves
can be invaded but significant disease damage does not occur.
* Leaf tissue can be infected and develop disease damage until it is
completely expanded and unfurled.
* It is primarily the immature, unfurled leaflets and leaflet tips which
are susceptible to infection and disease damage.
* Susceptible leaves must be protected by fungicides during the critical
period from initiation through development to Growth Stage 5.
* Leaves that reach Growth Stage 6 without visible disease damage
will remain unaffected by anthracnose.
* Protection of leaves during their development through Growth Stage
5 can be provided only by fungicides.
* Fungicides applied at shorter intervals can protect more new leaves
and leaf tissue from infection.
* The pathogen remains active throughout the year.
* It is much easier to suppress anthracnose during periods that are
relatively unfavorable for disease.
* Anthracnose damage increases directly with the interval that fern
leaves remain wet each day.
PAGE 5-9
AVOIDING AND MINIMIZING ANTHRACNOSE
6.0 TO AVOID OR MINIMIZE ANTHRACNOSE
Exclusion of disease is the ultimate control strategy. Exclusion of fern
anthracnose pathogen, particularly from well-isolated ferneries, is quite
feasible. To develop an exclusion strategy, it is important to
understand how the pathogen can gain access to a fernery and to
avoid these events. Disease, once present, can be minimized through
several approaches that reduce secondary inoculum and limit the
uncontrolled spread of spores within the fernery.
6.1 Disease Exclusion As mentioned in Sections 3 and 5, it is
theoretically possible for spores to be transported by wind, but this is
probably rare. It is unlikely that wind serves as a major mechanism of
wide-spread movement of this disease. Splashing and running water
can effectively spread C. acutatum spores within a fernery, but except
for special situations, long-distance movement in water from one
infested fernery to another is unlikely. New foci of disease (hot-spots)
can often be associated with animal movements; rodents may be
particularly important in this regard. For example, when rats or rabbits
forage among wet fern leaves, anthracnose spores can adhere to their
fur and be transported to other areas of the fernery. Rodents could
also transport spores to adjacent ferneries during foraging trips, but
they cannot be blamed for long distance movement of the pathogen.
Obviously, long distance movement of spores from one fernery to
another requires assistance. This assistance is commonly provided by
transport on clothing, tools, vehicles, and equipment. To exclude the
anthracnose pathogen from non-infested shadehouses or ferneries,
expected sources and the relative amounts of primary inoculum they
provide should be understood (Section 5.3). To exclude primary
inoculum, it is imperative to restrict access to ferneries to only
essential persons, vehicles, and equipment. Moreover, to prevent
essential equipment or persons from introducing primary inoculum,
decontamination, protective clothing, or other precautions may be
required (Section 6.3). For example, gates to shadehouses should be
chained to restrict vehicular traffic because soil containing spores of
the pathogen can easily be picked up and carried in tire treads.
Spores can also be carried on the surfaces of vehicles and equipment.
Accordingly, many initial disease foci are found adjacent to roadways.
Mapping of foci (Section 9) is often helpful to identify how primary
inoculum was introduced.
In summary, knowledge of sources and amounts of primary inoculum
will suggest the best methods to avoid their introduction. Section 6.3
discusses decontamination measures that can be used when the
presence or likelihood of the pathogen is suspected. Given the
seriousness of an anthracnose outbreak, and costs involved with
combatting it, preventative decontamination may be justified.
Exclusion is the best disease control
strategy. Anthracnose can be
avoided.
Splashing and running water can
spread the spores of the anthracnose
fungus over short distances.
Rodents may also be important in
short-distance spread of spores.
The primary method of short- and
long-distance spread of anthracnose
is the transport of fungal spores on
clothing, tools, and equipment.
Access to ferneries should be
restricted to essential personnel and
equipment.
PAGE 6 1
AVOIDING AND MINIMIZING ANTHRACNOSE
Sanitation reduces the amount of
disease and reduces the number of
spores of the fungus that are
available for spreading disease.
Sanitation methods can also help to
prohibit the spread of spores.
Diseased leaves should be removed
and burned or composted. Packing
house debris should be burned or
taken to a landfill.
Vehicles and equipment can easily
spread anthracnose spores over short
or long distances. Routine or
preventative decontamination may be
required.
Workers should wear freshly-
laundered or protective clothing and
either decontaminate shoes and
boots or wear protective footwear.
6.2 Sanitation in Ferneries Sanitation refers to methods aimed at
reducing inoculum levels or slowing the spread of inoculum within
infested ferneries. There are several ways to go about this which
depend greatly on the particular production system. However, the
principles are the same avoid primary inoculum, remove and
destroy diseased material to reduce available amounts of primary and
secondary inoculum (Section 5.4), and avoid or prevent the
uncontrolled spread of secondary inoculum. Many of the ways that
spores can be transported between ferneries are also efficient means
of spread within ferneries. Thus, some sanitation practices can help
prevent the introduction of anthracnose into previously uninfested
ferneries, whereas others are more appropriate to reduce the spread
of spores within infested ferneries. For example, sanitation with regard
to vehicles and equipment can reduce chances of unintentional
introduction of spores to new locations. An example of reducing the
amount of secondary inoculum available for potential spread within a
fernery would be to remove and properly dispose of diseased leaves
when fronds are harvested or ferneries are thinned or mowed. Often,
the debris is dumped in roadways. However, if this material is
diseased, spores can be unintentionally picked up by vehicles and
workers and transported throughout the fernery. Diseased fern debris
should be burned or transported to a landfill. Additionally, fern debris
discarded at packing houses should not be thrown out where vehicles
or workers can contact it and unknowingly transport spores.
When wet, spores can be rubbed from infected leaves directly onto the
surfaces of passing vehicles and equipment. This means of spore
movement can be substantiated by noting that fern leaves directly
adjacent to roadways usually have a higher incidence of disease than
those away from the road. Simple approaches such as widening
roadways within ferneries so that fern fonds do not rub against the
sides of vehicles would help in reducing the spread of anthracnose
spores. Movement of vehicles, workers and equipment can also be
directed from lightly to severely-infested ferneries.
When contact of vehicles, tools, and equipment with spores is
unavoidable or suspected, decontamination and cleaning is necessary.
If the probability of contamination is unknown, the equipment should
be cleaned before entering ferneries as a precautionary measure.
Section 6.3 addresses solutions to the problems of workers spreading
inoculum while Section 6.4 deals with decontamination of equipment.
6.3 Workers and Clothing Contaminated clothing, hand tools, and
small equipment are probably the major mechanisms of spore
movement between ferneries and are important vectors for
disseminating spores within ferneries as well. As workers bend over
and cut fern, their shoes and clothing can easily transfer spores from
diseased leaves to other susceptible leaves. Fern cutters should be
PAGE 6-2
AVOIDING AND MINIMIZING ANTHRACNOSE
instructed to first (early in the day) cut in areas where there is little or
no incidence of anthracnose and later, harvest in more severely-
damaged areas. Workers should also be encouraged to wear freshly-
laundered clothing each day because experiments have shown that
spores can maintain their viability for four weeks on clothing. However,
anthracnose spores are very sensitive to desiccation and cannot
survive laundering or the heat of laundry dryers. Footwear should also
be washed or decontaminated when entering and leaving ferneries.
Disposable protective clothing including gloves and shoe coverings are
possible solutions.
6.4 Decontamination of Equipment with Chemicals Surfaces of
vehicles and farm equipment that contact diseased fern should be
washed or decontaminated between uses. A number of quaternary
ammonium surface disinfectants may be suitable and most are very
effective in killing anthracnose spores. For skin decontamination,
Galloway GX 1027 hand soap can be used. For equipment, Gallex
900, Green-Shield, Physan, Prevent@, R*D*20, and Zepamine
A may be suitable. However, kill rates are deceptive when
determined under laboratory conditions; rates are much lower when
organic matter and soil are present. Use the recommended labeled
rates and methods for these compounds. Soap and water can also be
useful to reduce the amount of inoculum that contaminates vehicles
and equipment. Household bleach is effective in killing anthracnose
spores but it is corrosive. Under laboratory conditions, household
bleach kills spores at dilutions as low as 1: 1000, but when soil and
organic matter are present, kill rates are greatly reduced. As a surface
disinfectant, a concentration of at least 25% bleach should be used.
Other household compounds such as hydrogen peroxide, rubbing
alcohol (70% isopropanol) and PineSol are much less effective in
killing spores than the previously mentioned compounds and products.
Some quaternary ammonium compounds are also labeled as foliar
sprays for control of Botrytis blossom blight on orchids; however,
research clearly indicates that these (and similar compounds), are not
effective when sprayed on fern to control or eradicate anthracnose and
severe damage to fern can result when they are applied at high rates.
6.5 Burning and Mowing These techniques are used to help
rehabilitate severely damaged hot spots and ferneries. When a
propane torch is used to ignite and burn the thatch layer under the
fern, most of the fungal spores that reside there are also killed, so part
of the effectiveness of burning is due to greatly lowering local spore
populations. Burning also kills all newly-emerging fronds leaving none
available for infection. This temporarily stops or greatly slows the
disease cycle. It takes nearly a month for new fronds to emerge. By
this time, spore concentrations in the soil will have decreased to levels
where very few of the fronds will be re-infected (Section 5.2).
Several products are available for
washing and decontaminating tools,
equipment, and vehicles.
Products sold for decontamination of
equipment will not eradicate
anthracnose from fern plants.
Burning and mowing are very useful
to rehabilitate severely infested
ferneries or for supplemental
treatment of hot-spots.
PAGE 6-3
AVOIDING AND MINIMIZING ANTHRACNOSE
Protective fungicides must be
judiciously applied to fern leaves that
emerge after burning or mowing.
Mowed leaves do not have to be
removed.
Eradication of anthracnose from
ferneries is unlikely. Reports of
eradication are probably inaccurate.
Additional benefits may be gained if protectant fungicides are
judiciously applied to the newly-emerging fronds. Disadvantages to
burning are that it is labor intensive, can easily damage shade cloth,
and may be illegal in certain areas. Also, re-growth and frond
production may be adversely affected since the first new leaves are
small and not salable.
Mowing or weed-whacking can also be used to rehabilitate badly-
infested areas. The mowing process will spread anthracnose spores,
but it will also enable easy and efficient application of protectant
fungicides onto newly emerging fronds. For reasons discussed in
Section 5, Colletotrichum acutatum does not survive long in the
mowed leaves nor immediately provide a continuing source of
abundant inoculum; normally mowed leaves are not removed from the
fernery. However, research indicates the pathogen does survive at low
levels mainly in the lower portions (bases) of petioles (Figure 5).
Thus, protectant fungicides must be judiciously applied to the newly
emerging fronds. The new fronds produced after mowing are not as
stunted as those produced after burning. Recovery of mowed areas
and time required for a return to production status varies with the
season; late winter or early spring appear to be optimum times to
mow. Mowing has been very effective in rehabilitating severely
damaged ferneries and is widely used. Burning is less common.
6.6 Is Eradication Feasible? It is unlikely that the fern
anthracnose pathogen can be easily eradicated from an infested
fernery. Although several compounds have been tested, eradication
has not been achieved. Reports of eradication are probably
inaccurate; anthracnose has likely been reduced to levels not visible to
the casual observer. Given enough time and favorable conditions, the
disease will increase again to obvious levels. If intense fungicide
programs reduce disease to apparently undetectable levels, do not
discontinue all fungicide applications. However, depending on the time
of year, application frequency may be reduced to that appropriate for
preventative maintenance. In such a situation, there is a possibility
that over a long period of effective disease suppression, the disease
could be eliminated from that particular production unit, but we have
not yet had enough experience with anthracnose to fully determine
this. As an example, fern anthracnose has persisted in Central
American production regions since 1981 despite intensive fungicide
programs. Eradication might be achieved by destroying all fern,
waiting for a sufficient time (months) and replanting with disease-free
fern. Soil fumigation has resulted in non-detectable levels of fern
anthracnose. In the absence of such extraordinary measures, it is
probably appropriate to discount the possibility of eradication.
PAGE 6-4
AVOIDING AND MINIMIZING ANTHRACNOSE
SUMMARY OF SECTION 6 TO AVOID OR MINIMIZE
ANTHRACNOSE
* Exclusion of disease is the ultimate control strategy.
* Disease, once present, can be minimized.
* Splashing and running water effectively spread C. acutatum spores.
* Long distance movement in water is unlikely.
* Rodents can pick up spores on their fur, especially when wet, and
transport them throughout the fernery while foraging.
* Rodents can also transport spores to adjacent ferneries.
* Spores are most often spread by workers' clothing, tools, vehicles,
and equipment.
* Restrict access to ferneries to essential persons, vehicles, and
equipment.
* Before entering ferneries, decontamination, protective clothing, or
other precautions may be justified.
* Along with soil, spores are easily picked up and carried in tire treads.
* Spores are easily carried on the surfaces of vehicles and equipment.
* Sanitation refers to methods that reduce spore levels and slow the
spread of inoculum.
* Key principles of sanitation are to avoid primary inoculum and
remove and destroy diseased material.
* Remove and properly dispose of diseased leaves when harvesting or
thinning.
* Fern debris from packing houses should be burned or taken to a
landfill.
* When diseased fern leaves are wet, spores are easily transferred
onto objects that come in contact with them.
* If contact of diseased plants with vehicles, tools, or equipment is
unavoidable or suspected, decontamination or cleaning is
justified.
* Contaminated clothing, hand tools, and small equipment are the
major mechanisms of spore movement within and between
ferneries.
* Disposable, protective clothing can be used for workers and scouts.
* Several products are effective for decontaminating equipment,
shoes, and vehicles.
* Burning and mowing are very effective for rehabilitating severely
damaged hot spots or entire ferneries.
* Burning kills most spores and all newly-emerging fronds; it
temporarily stops or greatly slows the disease cycle.
* Normally, dead leaves are not removed from the fernery after
mowing.
PAGE 6-5
AVOIDING AND MINIMIZING ANTHRACNOSE
* Following mowing, the pathogen survives at low levels, mainly in the
bases of petioles.
* After burning or mowing, protectant fungicides must be frequently
and judiciously applied to the new fronds that emerge.
* It is unlikely that the fern anthracnose pathogen can be eradicated
from an infested fernery.
* Reports of eradication are probably inaccurate; most likely,
anthracnose has been temporarily reduced to low levels.
* Fern anthracnose has persisted in Central American production
regions since 1981 despite very intensive fungicide programs.
PAGE 6-6
FUNGICIDES FOR MANAGING ANTHRACNOSE
7.0 FUNGICIDES FOR MANAGING ANTHRACNOSE
7.1 How Fungicides Suppress Anthracnose Fungicides protect
young, susceptible fern leaves from becoming infected by the
anthracnose pathogen in two fundamental ways which depend upon
the type of fungicide used. A broad group of contact protectantt) type
fungicides such as mancozeb and chlorothalonil (Dithane T&O,
Protect, and Daconil/Echo/Thalonil) prevent spores that contact the
treated leaf from germinating and forming germ tubes, thus preventing
leaf penetration and infection. These fungicides may kill some spores
on contact, but their principle mode of action is to inhibit spore
germination. They have limited ability to eradicate the fungus within
the fern leaf or to inhibit spore production on diseased tissue. To be
effective, these fungicides must be present on the leaf surface at an
effective concentration when the spore arrives or when favorable
conditions induce spores already present to germinate (Reference 4).
A second major class of fungicides used on fern are the demethylase-
inhibiting or demethylation-inhibiting (DMI) fungicides. Examples are
propiconazole and myclobutanil (Banner, Systhane). Demethylation
is a physiological process essential for the biosynthesis of sterols and
other compounds required by the fungus to grow and reproduce. DMI
fungicides inhibit a key step in this process. This is why some
fungicides have previously been known as sterol-inhibiting fungicides
(Sl's). However, DMI is a more specific (and now preferred) term that
applies to the fungicides presently used on fern. DMI fungicides are
locally systemic. Evidence indicates that in fem they are only taken up
by the young leaves to which they are applied and are translocated
mostly within them. In leatherleaf fern, DMI fungicides do not appear
to move significantly from mature to immature leaves. Their systemic
nature in young leaves can be very beneficial. First, it provides greater
latitude in regard to the thoroughness of spray coverage required for
effective disease control. Since the fungicide is distributed throughout
the leaf, it better protects unfurling or expanding tissues and other
areas where an effective fungicide dose may not have been deposited.
Second, DMI fungicides can also suppress the growth of fungi which
have already infected the leaf. In fern, this activity affects infection
sites that occurred one and perhaps two to three days before the DMI
fungicide was applied. Systemic activity continues for only a few days
after the fungicide is applied. DMI fungicides are very useful but
expensive. They should be carefully used to prevent the pathogen
from developing resistance to them and to avoid phytotoxicity problems
(see References 4 and 7; Sections 7.6 and 7.7).
In summary, presently available fungicides do not work effectively to
eradicate the anthracnose fungus or to reduce sporulation on diseased
tissue. Mostly, they prevent new infections and therefore eventually
reduce populations of diseased leaves. Accordingly, populations of the
anthracnose fungus are also reduced.
Fungicides protect young, susceptible
fern leaves from becoming infected
by the anthracnose pathogen mostly
by preventing spore germination and
other processes that would normally
lead to leaf penetration and infection.
Fungicides can suppress, but do not
eradicate the anthracnose fungus.
PAGE 7- 1
FUNGICIDES FOR MANAGING ANTHRACNOSE
Protectant-type fungicides must be
present on the leaf surface when
spores arrive to inhibit spore
germination and infection. Some
other fungicides are locally systemic;
they are taken up by the young
leaves to which they are applied and
move systemically within the leaves
and protect them for a short period.
An effective dose of fungicide must
be applied to the young susceptible
leaves to protect them from becoming
diseased. Fungicide deposits must be
maintained on these leaves until they
are mature and no longer susceptible
to infection.
Various chemicals (including high
rates of fungicides) applied to the
older diseased leaves with the intent
of eradicating the fungus are not
effective.
7.2 Where and When Fungicides Must Be Placed The main
purpose of fungicides is to protect fern leaves from infection. They
should be applied to young leaves and coat exposed surfaces with an
effective dose. Systemic fungicides must also be applied to young
fern leaves to be taken up and move systemically within them. Fern
leaves need to be protected throughout the critical development period
from initiation through Growth Stage 6 when they are no longer
susceptible to infection. This period may last up to two weeks or
more. As leaves develop and expand, surfaces unprotected by
fungicides are continually being exposed; these surfaces must also be
protected. Once deposited on the fern leaf, some re-distribution of the
fungicide takes place through leaf wetting, but this process is often
inadequate to protect the new leaf surface area exposed and the new
leaves that emerge each day. Realistically, all new leaves cannot be
immediately protected. However, application intervals of 3-4 days
have produced acceptable results (Section 7.4). Research has shown
that even when DMI (or other systemic) fungicides are used, 3-4 day
application intervals should be maintained (Reference 13). Fungicide
deposits are also eroded by rainfall or irrigation and degraded by other
environmental factors. They reach ineffective levels within about 5-7
days after application. The above considerations help explain why fern
anthracnose has been very difficult to manage using traditional
approaches to disease control such as occasional or periodic fungicide
sprays. A partial solution to this problem is to employ shorter fungicide
application intervals than those traditionally used (Section 7.4).
The need for good spray coverage is obvious because an effective
dose of fungicide is needed to protect susceptible leaf surfaces.
Fungicide coverage and application rates are closely interrelated.
Application methods greatly influence spray coverage (Reference 4).
For example, it is possible to apply a correct rate of fungicide per acre
without adequately covering the targeted leaves. Conversely it is also
possible to cover targeted leaves with an inadequate dose of fungicide.
When adequate coverage of targeted leaves is attained, the
recommended rate per acre should provide an effective dose. Spray
coverage and droplet patterns can be checked with water-sensitive
indicating cards placed within the foliage, or by adding indicator dyes
to spray tanks. Several products are available for this purpose. Your
Extension Agent can provide sources of information for these methods.
In summary, an effective concentration of fungicide must be applied to,
and maintained on as many young susceptible leaves as possible to
adequately suppress fungal activity and reduce new infections to
acceptable levels. This can be achieved by employing more frequent
fungicide applications than have traditionally been used. Application
frequencies should be adjusted to reflect seasonal changes in disease
control requirements (Section 10). Various chemicals (including high
rates of fungicides) applied periodically to the older diseased leaves
with the intent of eradicating the fungus are not effective.
PAGE 7-2
FUNGICIDES FOR MANAGING ANTHRACNOSE
7.3 Application Methods Effective application methods enable the
correct placement of fungicides. If correctly utilized, any efficient
application method should work. There are advantages and
disadvantages to all and some may be better suited to one production
system than another or to certain fungicide products. Considerations
which cannot be compromised are correct placement on young
susceptible leaves, correct concentration or application rate/acre,
adequate coverage, and proper timing to protect most young fern
leaves from infection. Caution: Restrictions regarding application
methods permitted for specific fungicides are stated on product labels.
For example, some cannot be applied through irrigation systems.
7.3.1 Low-volume Application Methods For fern production, we
define low-volume application as obtaining adequate and uniform leaf
coverage without runoff by applying fungicides in 100 to 150 gallons of
water per acre. Tractor-mounted, backpack, hand-operated
pressure/hose, and air-blast sprayers have all been effective for
suppressing fern anthracnose. Low-volume sprayers require special
efforts to obtain good coverage of the young susceptible leaves where
it is needed most. For example, in a dense fern canopy, low-volume
or low-pressure sprayers are unlikely to obtain good coverage of young
developing leaves because sufficient amounts of spray are unlikely to
penetrate the canopy. However, such equipment may be effective on
small fern, new plantings, or on fern that have been recently mowed or
harvested (Section 6.5). In one series of experiments, a specially-
designed tractor-mounted sprayer that developed high pressure (350
Ib/in2) and employed several directed drop-nozzles was found to be
superior to chemigation, but equipment costs and the time needed to
apply fungicides were much greater. Perhaps low-volume methods
may be more appropriate for specialized, or more intense treatment of
small areas, disease foci, or when spray drift needs to be carefully
controlled as when spraying near workers, harvesting operations, or
dwellings. Air-blast sprayers are about as effective as chemigation.
Electrostatic and ultra-low volume sprayers have not been evaluated.
7.3.2 Chemigation At first glance, chemigation for anthracnose
control appears inefficient. It is amazing that it works at all. Research
on row crops has shown that without special adjuvants or formulations,
and using the lowest volume of water possible, only about 10% of the
applied chemical becomes deposited on leaves. There seems to be
little opportunity for fungicides to become more concentrated on leaves
than in the water in which they are applied, so the value of 10% seems
plausible. In chemigation, fungicides are often diluted to about 1/10 or
more of concentrations used for low-volume sprayers. In theory, this
should reduce the efficacy for control of a foliar disease, but
chemigation is becoming widely used on row crops. However, in
contrast to fern production, successful row crop chemigation permits
Effective fungicide application
methods provide the correct
placement of fungicides at effective
doses. If properly utilized, any
efficient application method should
work if it places effective
concentrations of fungicide on most
young, susceptible leaves.
In fern production, some fungicides
are commonly applied through
irrigation systems. This application
method can be effective for fern
anthracnose control. However, a few
fungicides effective against fern
anthracnose cannot presently be
applied through irrigation systems.
Check the product label before
attempting application.
PAGE 7 3
FUNGICIDES FOR MANAGING ANTHRACNOSE
To be effective for anthracnose
control, fungicides applied by
chemigation should be applied in the
smallest volume of water that
provides good coverage of the young
fern leaves.
Entire ferneries or hot spots that have
been severely damaged by fern
anthracnose can be rehabilitated with
supplemental fungicide applications.
moderate amounts of foliar damage by insects or disease because
success equates to no significant loss in yield (peanuts, soybeans etc.)
compared with low-volume application methods. Although disease
control requirements for fern are more demanding, experiments have
shown that chemigation (here it may also be called fungigation),
properly done, can effectively suppress or control fern anthracnose.
Acceptable control with fungigation depends on uniform coverage and
appropriate application strategies particularly timing and application
intervals. We support the contention that chemigation owes its
effectiveness to redistribution of fungicide to young leaves, so the role
of spray adjuvants is unknown and they should be used with caution.
Fungigation for anthracnose control is not the same as applying liquid
fertilizer. Effective fungigation requires application of fungicide in the
minimum volume of water needed to distribute it and apply it to young
foliage. For effective anthracnose control, a maximum amount of
fungicide should be deposited on the young foliage; it has no utility if
washed to the soil. Excess water applied after the fungicide clears the
system must be avoided. Excess water is detrimental and will dilute or
wash off the fungicide already deposited on leaves. Indicator dyes
added to fungicide concentrates and irrigation system pressure and
flow meters are used to determine the exact volume of water or
irrigation time needed for the fungicide to clear an irrigation system.
Uniform coverage by the irrigation system is essential for applying
pesticides and fertilizer. System requirements have been well covered
in References 4, 5 and 6. By using methods described in (Reference
5), both variation between sprinklers and system-wide irrigation
uniformity can be determined. The St. Johns River Water
Management District maximum water application rate for shadehouses
is 0.22 inches per acre per hour (approximately 100 gal-
lons/acre/minute). If other key factors are addressed (uniform
coverage, no excess washing of foliage after the fungicide clears the
system), fungigation is satisfactory for anthracnose control particularly
if the fungicide can be uniformly applied within a few minutes of
irrigation time (150-300 gallons/acre). Many fern growers with efficient
irrigation systems have applied fungicides in about 250-300
gallons/acre with good results. CAUTION: Special equipment and
precautions are required. Some fungicides labeled for fern cannot
legally be applied through an irrigation system.
7.3.3 Special Methods for Rehabilitation Even when fungicide
programs maintain disease damage at acceptable levels, disease foci
frequently remain. These foci, particularly when isolated and few in
number, can be targeted for special rehabilitative treatment. Mowing,
burning, marking, and avoiding contact with these areas (Sections 6
and 9) can be helpful. Populations of diseased plants within foci can
be significantly reduced with supplemental fungicide treatments.
PAGE 7-4
FUNGICIDES FOR MANAGING ANTHRACNOSE
It is usually cost-effective to apply supplemental treatments with
backpack, tractor-mounted, or hand sprayers. Maximum frequencies
and rates can be used, and, as the areas are small, little additional
cost is incurred. When treating a hot spot, it is essential to treat a
generous buffer zone surrounding it because disease is probably
present there as well, but not always obvious. No rule can suffice for
all situations, but an estimated guideline is to treat a buffer zone at
least twice the diameter of the affected area. Follow other guidelines
for fungicide application; excess rates or spray volumes are not
required. The key is more frequent applications with good coverage of
young leaves. It is essential to monitor treated areas to determine the
effectiveness of these special efforts.
7.4 Application Frequency of Fungicides Leaf initiation and
development helps determine the rate of disease increase.
Unprotected, susceptible leaf tissue is constantly being exposed
(Sections 4.2, 5.7 and 7.2). Moreover, fungicide deposits on treated
leaves are rapidly degraded (Reference 4). Available fungicides mainly
protect leaves, so there seems to be no alternative except to make
fungicide applications frequently enough to protect new and exposed,
susceptible leaf surfaces. Experiments have shown that for much of
the year, with moderate levels of disease present, 7-day application
intervals will not be effective, regardless of the type of fungicide used.
However, 3-4 day application intervals have produced acceptable
results (References 11, 12 and 13). For more intensive or
rehabilitative programs, 3 applications per week may be justified.
CAUTION At present, there may be no provisions for such frequent
applications on the labels of all fungicides labeled for leatherleaf fern;
most can only be applied at 7 to 10-day intervals. Efforts are
underway to modify labels of all appropriate fungicides to permit
shorter application intervals when needed. These uses will require
better planning to meet worker re-entry requirements. Check with your
Extension Agent for the latest regulations concerning this limitation.
It is probably impractical to spray more often, but in serious disease
situations, 2-3 fungicide applications per week may be justified. Such
frequent applications are needed to suppress anthracnose to levels
where a normal maintenance program can suffice. It should not be
necessary to continue such intensive spray programs for more than a
few weeks. If inspection (scouting) indicates proportions of new
diseased leaves have been substantially reduced, application intervals
may be lengthened accordingly (Sections 5, 7.4, 8 and 9). Seasonal
aspects of disease management are also important in determining
application intervals. At some times of the year, depending on disease
levels present, 7-day intervals can be effective. This approach
requires weekly monitoring to verify that disease continues to be sup-
pressed to acceptable levels (see Section 9).
The key to controlling fern
anthracnose with fungicides is to use
an application frequency that will
protect most new leaves. The
appropriate application frequency will
change with the seasons of the year.
Calendar based applications and
spray programs are totally
unsatisfactory for fern anthracnose
management.
PAGE 7 5
FUNGICIDES FOR MANAGING ANTHRACNOSE
Fungicides, if improperly used, can
cause serious injury to leatherleaf
fern and reduce frond vase life. The
type of fungicide, application rate,
application method and frequency,
and weather can also influence leaf
injury caused by fungicides.
DMI fungicides (sterol-inhibiting
fungicides) require special
precautions when used on leatherleaf
fern.
To summarize, application interval should be determined by consider-
ing several factors. Season must be considered and some type of
scouting will be required to determine when and if application
frequencies can be altered (Sections 9 and 10). Calendar-based
applications have proven to be totally unsatisfactory for anthracnose
management.
7.5 Fungicide Rates Fungicide recommendations made by
University Extension Specialists reflect the product label which will
state general use rates and application methods for "ornamentals" or a
specific rate and application interval for leatherleaf fern. Fungicides
which do not work using rates and methods consistent with product
labels, will not be recommended. Exceeding the recommended rate
wastes money and places growers out of compliance with pesticide
laws. Excessive application rates and frequencies have also been
shown to damage fern and can have detrimental effects on vase life of
harvested fronds. Product labels reflect environmental safety concerns
and extensive efficacy testing. Fern anthracnose can be managed
effectively by following the product labels. There is no need nor
justification for deviating from labeled use patterns and rates.
With most plant diseases, using less than the recommended rate, even
if tank-mixed with another fungicide (when permitted by pesticide
regulations) will not always provide effective protection for leaves.
However, in the special case of fern anthracnose, application
frequency may be somewhat more important than using maximum
rates. There is evidence that minimum rates, if applied frequently
enough (3-4 day intervals), can be effective. This approach is being
investigated. If effective, it will be reflected in future recommendations.
7.6 Fungicide Toxicity to Leatherleaf Fern Excess fungicide rates
and application frequencies can damage fern leaves. Beside chronic
toxicity problems including reduced vase life (propensity for harvested
fronds to wilt), excess fungicide can damage, burn, or scorch fern
leaves. Some types of fungicide toxicity can occur on leaves that were
immature when the fungicide was applied; others can occur on mature
leaves. If fungicide label recommendations are followed, this type of
injury will be relatively infrequent since the absence of phytotoxicity is
an essential criterion for fungicide labeling.
Demethylation inhibitor (DMI) fungicides have routinely caused fern
injury that varies considerably with the product, in the type of injury,
and the growth stages of leaves that are damaged. Injury from DMI's
commonly appears one to five days after application. A bronze to
yellow streaking or blotching can be produced on leaves in Growth
Stage 5-6, but mature leaves can also be affected. Sometimes, DMI
fungicides can damage leaves in Growth Stage 3-4 and cause a
PAGE 7-6
FUNGICIDES FOR MANAGING ANTHRACNOSE
blackening of leaflet tips similar to anthracnose and some types of
freezing injury. Spray adjuvants and tank-mixing with other pesticides
have usually intensified phytotoxicity from DMI fungicides.
Labels for some DMI fungicides used on leatherleaf fern suggest that
trial applications be made to see if injury occurs. Some DMI's
occasionally cause injury even when used at rates and frequencies
consistent with the label. Others cause no injury at all except under
unusual, and poorly defined, circumstances. Research is currently
underway to investigate external factors that enhance injury. Cold
weather is clearly one factor. Experiments have shown that fern can
be injured when DMI fungicides are applied before or following
intervals (1-3 days) of cold temperatures (< 40 C, 40 F); injury
occurred even if subsequent temperatures remained relatively warm.
Also, grower reports of injury from DMI fungicides have predominantly
occurred during the winter season. For the present, it is probably best
to avoid DMI fungicides during cold weather and to check periodically
with your Extension Agent regarding the current status of this problem.
DMI fungicides produce plant growth regulator-like effects in many crop
and weed species. Growth rates and development may be seriously
affected. However, none of these effects have been observed on
leatherleaf fern except when experimental fungicides have been used
routinely and at excess rates for long periods (References 11 and 12).
Growth and development defects in young fern fronds have probably
resulted from accumulation of excess amounts of DMI fungicides in the
soil (References 7, 11 and 12). This is not unexpected. Many DMI
fungicides are persistent and do not break down very rapidly,
particularly in soil. DMI fungicides can accumulate in soil, be taken up
by roots, and affect growth and development. For fern, the amounts
involved or duration of these effects have not been determined.
7.7 Fungicides and Pathogen Resistance Of the fungicides likely
to be used for anthracnose management, only those in the class
known as demethylation-inhibitors (DMI's) present significant
opportunities for the anthracnose pathogen to become resistant to
them. If resistance develops, the fungicide will have only minimal
effects on the pathogen and the disease will not be controlled.
Unfortunately, if the fungus develops resistance to one DMI fungicide,
it will likely be resistant to all. Several useful DMI fungicides are
currently in various stages of development and labeling for fern. It
would be unfortunate if C. acutatum develops resistance to all of them.
Briefly, if DMI fungicides are used exclusively, routinely, or too
frequently, chances of the pathogen developing resistance to them are
greatly enhanced. For this reason, DMI's should be used infrequently
and always in alternation with other classes of fungicides that present
negligible opportunities for pathogen resistance. Guidelines for the use
of DMI fungicides in fern production have been discussed in
Factors such as cold weather or
spray adjuvants can increase the
likelihood of fern injury by DMI
fungicides.
Improper use patterns with any DMI
fungicide may result in the
anthracnose fungus becoming
resistant to all DMI fungicides.
PAGE 7-7
FUNGICIDES FOR MANAGING ANTHRACNOSE
There are several possible strategies
for using fungicides effectively without
creating additional problems for
leatherleaf fern production. These
strategies depend upon the types of
fungicides used.
All fungicides are not effective against
fern anthracnose, but many are
suitable when properly used. No
single fungicide has been found to
control anthracnose when applied at
application intervals of 7 days or
more.
References 4 and 7. Pathogen resistance to other fungicides used on
fern is probably not a significant possibility even with frequent and
exclusive use. However, there are other reasons for alternating
fungicides that are discussed in Sections 7.6 and 7.8.
7.8 Fungicide Programs for Managing Anthracnose There are
three major considerations for developing effective fungicide control
strategies for fern anthracnose. First, and most important, is
application frequency. Seven-day application intervals are not effective
for suppressing or controlling anthracnose during warm weather and
frequent rains; 3- or 4-day intervals are much more effective when
intensive fungicide programs are required. In cool seasons, and in
some situations, 7-day intervals will be adequate (Reference 13).
Second, only effective fungicides should be used. All fungicides are
not effective against fern anthracnose, but many are acceptable
(References 9, 11, 12 and 13). Some are more effective than others,
easier to use, cover better, last longer, or cost less. However,
research has not identified a single fungicide that will consistently
provide acceptable control of anthracnose when applied at traditional
7- to 10-day intervals. Disease management, utilizing several fungi-
cides effectively, is the only viable approach to anthracnose control.
Third, fungicide products should be used in an alternating sequence to
take full advantage of their best properties while avoiding potential
problems associated with frequent or exclusive use. Cost is also a
consideration. A few examples will illustrate this approach.
Example 1: There are other important diseases of leatherleaf
fern such as Cylindrocladium and Rhizoctonia. Not all fungicides
useful for anthracnose provide acceptable control of these diseases,
so it is appropriate to alternate two or three different contact-protectant
fungicides that do. Cost and product preference are also important,
and less costly products (if effective) can be part of such a program.
Another consideration is that many fungicides contain manganese (Mn)
or zinc (Zn). Although these fungicides supply some micronutrients to
fern (Reference 5 and Section 4.2.2), prolonged and continued use
may result in excessive and potentially toxic concentrations of Mn and
Zn in fernery soils. Thus, non-metal containing fungicides should be
part of a alternating fungicide sequence. Fungicide cost is not strongly
related to efficacy, but when conditions are relatively unfavorable for
disease, less costly fungicides can be included in such a program and
still provide acceptable results. In this example, two or three contact-
type, protectant fungicides might be alternately applied at appropriate
frequencies (Sections 5.8, 7.4 and 10.3). There is no compelling
reason to use one fungicide for one application and different one for
the next, or the same one twice in a row. Alternating fungicides is the
key. Products may also be alternated and results should be similar.
PAGE 7-8
FUNGICIDES FOR MANAGING ANTHRACNOSE
Example 2: In this example, a DMI fungicide is introduced into
the program. This approach is very different from Example 1. It
requires more planning and scheduling. For reasons presented in
Sections 7.2 through 7.7, DMI's not only tend to be more effective but
also more expensive and complicated to use. The DMI will make a
difference because its systemic properties make it more effective in
preventing infections during the period in which that particular
application remains active (Sections 7.2 through 7.3). For reasons
outlined in References 4 and 7 and Sections 7.6 and 7.7, DMI
fungicides should not be used often or routinely, so alternating them
with other fungicides is essential. Alternating one DMI fungicide
with another is not recommended for the same reasons.
Occasional or periodic use of a DMI fungicide in alternation with
contact protectant fungicides (perhaps 1 week out of 4) can be
advantageous particularly under conditions favorable for disease
development. Some DMI product labels specify how often they can be
applied per crop or per year, but some do not. We do not recommend
frequent or prolonged use of DMI fungicides to leatherleaf fem.
Finally, DMI fungicides should be used with caution or not at all when
cold weather is possible (Section 7.6).
A typical intensive-type program that employs a DMI fungicide might be
as follows: Two applications per week are made. The first week, a DMI
fungicide is applied; later in the week, an ethylene-bis-dithio-carbamate
(EBDC) type fungicide (example: mancozeb) is also applied. The
second week, two applications are also made; one might be a
chlorothalonil product and the second, an EBDC-type fungicide. The
third week is the same as the second week. For the fourth week, the
cycle begins again with the DMI fungicide followed later in the week by
an EBDC fungicide. This approach exploits the advantages of DMI
fungicides and minimizes their potential hazards.
The fungicide program examples described above are more complex
than those traditionally used. They require more careful planning to
avoid conflicts with harvesting activities and worker protection and re-
entry standards. They are very general because it is beyond the
scope of this manual to list specific fungicides (except to provide
examples) or make fungicide recommendations because product
availability and labels will change. New fungicides will become
available. Some tank-mixes have appeared particularly promising, but
more research is needed in this area. Unexpected problems may also
be encountered after long-term product use or when mixing fungicides.
Your Extension Agent and fungicide supplier can assist you regarding
the current status of products, fungicide programs, and
recommendations. Extension publications, newsletters, and current
product information are key sources. With the information gained from
this manual, you should be able to effectively conduct your own
evaluation of programs, products and management techniques and
avoid most potential problems associated with fungicide use.
DMI fungicides, in particular, present
special and potentially serious
problems if improperly used.
These fungicide programs are more
complex than those traditionally used
and require careful planning to avoid
conflicts with harvesting and worker
protection and re-entry standards.
This manual does not recommend
specific fungicides for fern
anthracnose control. Contact your
Extension Agent or fungicide supplier
for information on the current status
of products and recommended
fungicide programs for leatherleaf
fern and fern anthracnose.
PAGE 7 9
FUNGICIDES FOR MANAGING ANTHRACNOSE
SUMMARY OF SECTION 7 FUNGICIDES FOR MANAGING
ANTHRACNOSE
* Fungicides protect young, susceptible fern leaves from being
infected by the anthracnose pathogen.
* Mode of action depends upon the type of fungicide used.
* Contact protectantt) fungicides prevent spores that contact the
treated leaf from germinating and forming germ tubes which
would normally lead to leaf infection.
* Protectant fungicides have little ability to eradicate the fungus within
the fern leaf or to inhibit spore production. They prevent new
infections and reduce populations of diseased leaves.
* Fungicides must be present at an effective concentration on the leaf
surface when the spore arrives, or favorable conditions induce
spores already present to germinate.
* Fungicides applied to older diseased leaves with the intent of
eradicating the fungus are not effective.
* An important class of fungicides used on ferns are the
demethylation-inhibiting (DMI) fungicides sometimes called
sterol-inhibiting fungicides (Sl's).
* DMI fungicides are locally systemic; they are taken up by the young
fern leaves that they contact and are translocated within them.
* DMI's provide greater latitude in regard to the thoroughness of spray
coverage required for effective disease control.
* Since DMI fungicides move throughout the young leaves that they
contact, hard to protect tissues (including unfurling or
expanding leaf tissues and areas where an effective dose may
not have been deposited) can also be protected.
* DMI fungicides can inhibit the growth of fungi which have infected
the leaf as much as 2 days before the fungicide was applied.
* DMI's must be used with care to prevent the pathogen from
developing resistance to them and to avoid phytotoxicity prob-
lems.
* Since the main purpose of fungicides is to protect most fern leaves
from infection; it will require shorter fungicide application
intervals than those traditionally used.
* Good spray coverage is required to provide the effective dose of
fungicide needed to protect susceptible leaf surfaces.
* Application methods greatly influence fungicide coverage.
* Spray coverage and droplet patterns can be checked with water-
sensitive indicating cards or by adding indicator dyes to spray
tanks.
PAGE 7 10
FUNGICIDES FOR MANAGING ANTHRACNOSE
* Application frequencies can be varied to reflect seasonal changes in
disease control requirements.
* If correctly utilized, any efficient application method will work.
* Tractor-mounted sprayers, backpack sprayers, hand-operated
pressure/hose sprayers, and air-blast sprayers are all effective
for suppressing fern anthracnose.
* Low-volume sprayers require special efforts to obtain good coverage
of young leaves.
* Low-volume methods may be more appropriate for specialized, or
more intense treatment of small areas, or when human
exposure or spray drift must be minimized.
* Chemigation (fungigation), properly done, can effectively suppress or
control fern anthracnose.
* Successful chemigation depends on uniform coverage and
appropriate application strategies.
* Effective fungigation requires application of fungicides in the
minimum volume of water needed to carry and apply it to
young foliage.
* A maximum amount of fungicide should be deposited on the young
foliage; excess water applied after the fungicide clears the
system will dilute or wash off the fungicide already deposited
on leaves.
* If other key factors are addressed, fungigation is satisfactory for
anthracnose control particularly if the fungicide can be
uniformly applied within a few minutes of irrigation time (100-
300 gallons/acre).
* Foci (hot spots) can be targeted for special rehabilitative treatment;
populations of diseased plants can be significantly reduced
with supplemental fungicide treatments.
* It is cost-effective to apply supplemental treatments with backpack,
tractor-mounted, or hand sprayers.
* When treating a hot spot, it is essential to treat a generous buffer
zone surrounding it, because disease is probably present there
but not obvious.
* Fungicides must be applied frequently enough to protect most
exposed, susceptible leaf surfaces.
* 3-4 day application intervals have produced acceptable control.
* At present, no fungicides labeled for leatherleaf fern permit such
frequent applications; most can only be applied at 7- to 10-day
intervals.
* Attempts are now being made to change fungicide labels to allow
more frequent applications to leatherleaf fern check product
labels before use.
* In serious disease situations, 2 3 fungicide applications per week
may be justified.
PAGE 7 11
FUNGICIDES FOR MANAGING ANTHRACNOSE
* Seasonal aspects of disease management are also important in
determining fungicide application intervals. This approach
requires monitoring to verify that disease continues to be sup-
pressed to acceptable levels.
* Calendar-based applications are totally unsatisfactory for
anthracnose management.
* Fungicides which do not work at a rate consistent with the label will
not be recommended for fern anthracnose control.
* Excessive application rates and frequencies can damage fern and
reduce vase life of harvested fronds.
* Fern anthracnose can be managed effectively by following product
labels. There is no need or justification for deviating from
labeled use patterns and rates.
* Spray adjuvants and tank-mixing with other pesticides have usually
intensified phytotoxicity from DMI fungicides.
* External factors that enhance injury from DMI fungicides are being
investigated.
* Reports of injury from DMI fungicides have occurred predominantly
during the winter season.
* It is probably best to avoid DMI fungicides during cold weather.
* DMI fungicides produce plant growth regulation effects in many crop
and weed species; they have not been observed on leatherleaf
fern except when experimental fungicides have been used
excessively for extended periods.
* Growth and development defects in young fern fronds have probably
resulted from accumulation of excess amounts of DMI
fungicides in the soil.
* Of the fungicides likely to be used for anthracnose management,
only DMI's present significant opportunities for the anthracnose
pathogen to become resistant to them.
* If the fungus develops resistance to one DMI fungicide, it will likely
be resistant to all.
* If DMI fungicides are used exclusively, routinely, or too frequently,
chances of the pathogen developing resistance to them are
greatly enhanced.
* DMI's should be used infrequently and always in alternation with
other classes of fungicides.
* Most fungicides used on ferns, other than DMI's present negligible
opportunities for pathogen resistance.
* Prolonged and continued use of metal-containing fungicides may
result in excessive and potentially toxic concentrations of Mn
and Zn in fernery soils.
* Non-metal containing fungicides should be part of a alternating
fungicide program.
* Frequent or prolonged use of DMI fungicides on leatherleaf fern is
not recommended.
PAGE 7 12
CULTURAL METHODS
8.0 CULTURAL AND PRODUCTION METHODS TO MANAGE
ANTHRACNOSE
Cultural activities (or the absence of them) greatly influence the
success or failure of disease control. They are a key part of plant
disease management. Fungicides alone will not provide acceptable
results unless they are well-integrated with cultural practices that avoid
disease or are detrimental to disease progress. On the other hand,
inappropriate cultural activities can counteract almost all benefits
provided by fungicides and often lead to disease situations that
overwhelm most economically viable or legal fungicide programs.
8.1 Avoiding Local Spread and Promoting Disease Many cultural
operations can spread anthracnose. Some of these activities can be
modified or performed at optimum times to reduce their potential for
spreading spores of the pathogen. Examples are once-over harvesting
and avoiding excessive irrigation or irrigating at night to avoid
prolonged leaf wetness periods. Other cultural operations such as
creating aisles between beds for better aeration and foliage drying are
designed to adversely affect disease development or spread.
Additional cultural opportunities for managing anthracnose are
discussed in Sections 2.2.3, 5.4, 5.5, 6.2, 6.3, 6.4, and 8.2.
8.2 Mowing and Burning for Rehabilitation These are important
cultural techniques that are useful for rehabilitating severely-damaged
ferneries, and hot-spots. Diseased foliage is mowed or burned but
rhizomes survive. New leaves that emerge must be protected by an
intensive fungicide program. Mowing has been increasingly used to
rehabilitate severely-damaged ferneries with excellent results. This
approach is discussed in Section 6.
8.3 Minimizing Irrigation Frequency and Wet Foliage Frequent
and prolonged intervals of wet foliage have a profound effect on
anthracnose development (see Section 5.5). Rain or irrigation-wetting
are not essential; dew is sufficient. Therefore, it is helpful to minimize
leaf wetness intervals by not extending natural wet periods or by
creating additional ones. For example, night-time or early-morning
irrigation or chemigation is one possible approach. As mentioned in
Sections 3.2 and 5.1 through 5.4, this strategy can minimize
opportunities for sporulation and dispersal of spores and help slow
disease development. However, spore germination and infection of
leaves occurs within 3 hours at 220 C [720 F], so opportunities to stop
infection by minimizing leaf wetness periods are unlikely. Unfortunately,
irrigation, or chemigation contribute to the wet-leaf problem. The
relative effectiveness of low-volume spraying (if young leaves are
covered) compared with chemigation may not be totally due to better
Cultural methods and activities have
a great effect on fern anthracnose.
Many essential activities can be
modified or scheduled so they do not
promote anthracnose. Other cultural
practices are detrimental to fern
anthracnose and are valuable
management techniques.
Anything that can be done to
minimize leaf wetness periods will be
helpful in reducing anthracnose
development.
Excessive irrigation can spread
inoculum and wash fungicides from
susceptible leaves.
PAGE 8-1
CULTURAL METHODS
Harvesting operations are particularly
important in spreading anthracnose
within and between ferneries but
many harvesting methods can be
modified to reduce their potential for
spreading inoculum.
Weeds and wild ferns are probably
not important sources of fern
anthracnose inoculum.
fungicide concentrations provided. It could be partially due to reduced
leaf wetting that accompanies low-volume spraying.
One of the predominant reasons growers irrigate is to apply liquid
fertilizers. Dry, slow- and controlled-release fertilizers can reduce or
totally eliminate the need to apply liquid fertilizers and minimize the
need to apply large amounts of irrigation water. This practice can also
reduce leaf wetting and fungicide erosion (Section 7.4 and 7.5).
Other cultural practices can help to reduce leaf wetness periods. For
example, thorough harvesting and removal of weeds and unnecessary
fern leaves helps prevent prolonged leaf wetness periods within the
canopy by increasing air flow. Aisles between fern beds could provide
similar benefits. Vertical shade cloth on the sides of structures that is
not essential for shading or freeze protection can be removed or
reconfigured in the summer to improve air flow into ferneries.
8.4 Considerations For Laborers and Harvesting Workers'
clothing and harvest equipment easily contact and transfer
anthracnose spores. Contaminated clothing and hand tools are
probably the major mechanisms of spore movement both within and
between ferneries. If possible, fern cutters should be instructed to first
harvest from areas with little or no incidence of anthracnose and later
cut in areas with greater levels of disease. The same considerations
apply to vehicles and equipment. Workers can also be encouraged to
wear freshly-laundered clothing each day; protective clothing is also an
option (Section 6). In ferneries, any activity should be avoided when
foliage is wet or during rainfall, particularly harvesting operations (see
Sections 5 and 6). It is also helpful to plan for minimum contact with
fern in infested ferneries. For example, minimize the frequency of
harvesting and weeding activities. Individual production units should
be thoroughly cut-over, or weeded once rather than making multiple
harvests over time (see Section 6).
8.5 Role of Weeds and Wild Ferns Colletotrichum acutatum can
infect several species of wild and cultivated ferns, but apparently does
not infect other weeds or plant species. At present, the role of other
fern species in establishing or maintaining the disease on leatherleaf
fern is unknown. However, anthracnose has severely damaged holly
fern (Cyrtomium falcatum) being grown for cut foliage. Anthracnose
can also infect and damage several wild ferns including bracken fern
(Reference 10) which are common in fern production areas. Thus far,
C. acutatum has not been found on any fern growing in the wild. It is
unlikely that any weed species, other cultivated, or wild ferns serve as
a source of primary inoculum but growers should be aware of the
possibility of other cultivated ferns as a potential source of inoculum or
as a potential target for inoculum produced on infected leatherleaf fern.
PAGE 8-2
CULTURAL METHODS
There are many good reasons for weed control in and around
ferneries. Except for improving aeration as discussed in Sections 8.1
and 8.2, weed control (excluding weeding activities of workers) will
probably have little effect on anthracnose. On the other hand,
leatherleaf fern growing near or outside diseased ferneries probably do
not receive any fungicide applications. The excellent dispersal
capabilities of the anthracnose fungus usually results in these plants
becoming diseased. Such volunteer fern plants should be considered
as weeds and removed since they are excellent, and continuing,
sources of anthracnose inoculum. Abandoned fern plantings, if
diseased, can also serve as inoculum sources and should probably be
destroyed.
SUMMARY OF SECTION 8 CULTURAL AND PRODUCTION
METHODS TO MANAGE ANTHRACNOSE
* Cultural methods are a key part of anthracnose management.
* Fungicides alone will not provide acceptable results unless well-
integrated with cultural practices that avoid disease or are
detrimental to disease progress.
* Inappropriate cultural activities can counteract almost all benefits
provided by fungicides.
* Many cultural operations can spread anthracnose; most can be
modified or better timed to avoid this.
* Mowing and burning are important cultural techniques that are useful
for rehabilitating severely damaged ferneries and foci or hot
spots.
* Minimize leaf wetness intervals and do not extend natural wet
periods or create additional ones.
* Unfortunately, irrigation and chemigation contribute to the wet-leaf
problem.
* Dry, slow- and controlled-release fertilizers can reduce or totally
eliminate the need to apply liquid fertilizers and minimize the
need to apply large amounts of irrigation water.
* Anything done to increase air flow in ferneries is beneficial in
reducing leaf wetness.
* Aisles between fern beds can reduce leaf wet periods.
* Workers' clothing, harvesting equipment, and hand tools are
probably the major mechanisms of spore movement both within
and between ferneries.
* Fern cutters should first harvest from areas with little or no incidence
of anthracnose and later cut in areas with greater levels of
disease. The same considerations apply to vehicles and
equipment.
* Workers should be encouraged to wear freshly-laundered or
protective clothing each day.
PAGE 8 3
CULTURAL METHODS
* Any activity in ferneries should be avoided when foliage is wet or
during rainfall, particularly harvesting operations.
* Plan for minimum contact with ferns in infested ferneries.
* Production units should be thoroughly cut-over or weeded once
rather than making multiple harvests.
* The role of other fern species in establishing or maintaining the
anthracnose on leatherleaf fern is unknown.
* Fern anthracnose has not been found on any wild fern species
growing in the wild.
* It is unlikely that any weed species, other cultivated or wild ferns
serve as a source of anthracnose.
* Weed control (excluding weeding activities of workers) will probably
have little effect on anthracnose.
* Leatherleaf fern growing near or outside infested ferneries can
become diseased; these volunteer fern plants should be
removed since they are excellent sources of anthracnose
inoculum.
* Abandoned fern plantings, if diseased, can also serve as inoculum
sources and should probably be destroyed.
PAGE 8-4
EVALUATING DISEASE MANAGEMENT
9.0 EVALUATING THE EFFECTIVENESS OF DISEASE
MANAGEMENT
To manage fern anthracnose, you need to know what is happening in
the fernery. This requires periodic inspection and sampling. Once
tried, the value of a monitoring program that provides timely and
quantitative information will become clear. Monitoring for fern
anthracnose is easily combined with methods for obtaining other useful
information on fern production and other fern pests. This process of
information gathering is also known as scouting.
CAUTION: During all scouting activities, take precautions discussed in
Section 6 to avoid introducing or spreading anthracnose. Re-entry into
pesticide-treated areas may require postponement or wearing
protective clothing. Good planning and occasionally, decontamination
may be required.
9.1 Scouting for Anthracnose Scouting for anthracnose can
detect the presence of disease at an early stage or determine the
extent of disease damage already present. Scouting can also assess
the efficacy of management strategies while providing a continuing
record of disease progress within a fernery or production unit. Until
more formal sampling methods are devised, a basic but useful method
is to walk the entire fernery and either examine or collect leaves. It is
easier to collect leaves and examine them later than to try to evaluate
them in the field, but on-site evaluation will work.
9.2 Sampling Units and Frequency Individual fern leaves are
natural units for sampling and evaluation. The proportion of sampled
leaves affected by disease and the extent of disease damage on these
leaves are excellent indicators of disease incidence and intensity. If
production units are sampled periodically, the results are particularly
useful to monitor disease progress, project future disease damage,
frond yields, and to compare management strategies. For example,
weekly scouting results plotted against time are excellent aids for
evaluating disease control programs; results can be seen within a week
or two following treatments or other activities (see Figures 9 and 10).
A specific production unit (shade structure, hammock, section or
perhaps an entire fernery) is a natural division for scouting purposes.
It is best to divide a fernery into a minimum number of sampling or
management units based upon factors such as age of planting, disease
damage, cultural history, disease control programs, or harvesting
activities. For example, units that are well-separated or grown under
different production systems (shade cloth vs. oak hammock,
chemigation vs air blast sprayer etc.) can be considered as distinct
units for scouting.
Scouting is a key component of
anthracnose management.
Periodic scouting provides a
continuing record of anthracnose
levels and allows you to make
informed decisions.
The almost-mature fern leaf (Growth
Stage 5) is the ideal unit for sampling
and disease assessment.
Production units with different cultural
systems, pest control, or
management programs should be
scouted separately.
PAGE 9 1
EVALUATING DISEASE MANAGEMENT
Scouting procedures can be very
simple or complex; they can be
modified to suit your requirements
and resources.
Scouting for anthracnose estimates
disease incidence and damage on the
leaves being sampled not the total
leaf population in the fernery.
Results reflect disease activity one or
two weeks prior to the sampling date.
To obtain an adequate sample, all
areas of the fernery must be
represented including disease foci.
However, any area of interest can be
sampled with these methods.
Statistically based sampling methods have not yet been established.
However, one effective approach has been to walk through and
randomly sample the entire production unit for anthracnose while
looking for other problems such as insects, insect damage,
malfunctioning irrigation, and fertility problems. By periodically
inspecting almost all areas of the unit, chances of detecting new
infection sites early or finding other problems are increased. For units
where anthracnose has not yet been found, field scouting without
taking leaf samples is probably adequate and much faster (see below).
When disease is present, more intensive sampling is needed to
estimate levels of disease incidence and damage. Experiments have
shown that approximately 150 leaves collected weekly from a 5-acre
unit were satisfactory to monitor disease progress and determine the
effectiveness of spray treatments (see Figure 10). This method
requires about 30 minutes to collect leaves and about 40 minutes to
evaluate them and record the data. Because of the short life cycle of
the anthracnose fungus, and continuous production of new, suscepti-
ble, fern leaves, weekly sampling is needed to monitor the
effectiveness of fungicide applications, control programs, and disease
management strategies. Sampling intervals can be extended slightly
during cooler seasons of the year (Section 10).
Leaves in Growth Stages 1-5 are susceptible to infection whereas
those in Stages 6 and 7 are not. If infected, leaves will almost always
show disease damage by Growth Stage 5-6. Healthy leaves in this
stage are unlikely to become diseased. Therefore, the best sampling
unit for monitoring anthracnose is the fern leaf at Growth Stage 5 or 6
(Figure 4). Sampling from this leaf population estimates the level of
infection and disease damage which occurred during the interval
between initiation and development to Stage 5 or 6. Generally, this
corresponds to the two-week period just prior to sampling. Disease is
estimated in the population being sampled and not in the total leaf
population present. When the disease status of a production unit is
unknown, it is easier and faster to spot initial disease by first searching
for infected, mature leaves because they are more obvious. Once
disease is found, the extent of infestation and damage can be
estimated with the sampling methods just discussed.
9.3 Basic Approaches to Sampling Leaves of an appropriate
growth stage can be collected at random, or sampling stations can be
established. For random sampling, use a walking pattern likely to
encounter representative portions of the entire unit. Leaves are picked
at random while walking the fernery. Sampling stations can also be
used. With this approach, several stations representative of the unit
are chosen and marked; foci or hot spots can be included. The
stations are visited each week and one or more leaves are collected in
the immediate vicinity. With any method, collected leaves should be
kept cool and out of the sun. In plastic bags exposed to sunlight,
PAGE 9-2
EVALUATING DISEASE MANAGEMENT
young fern leaves can be seriously damaged or wilt within 30 minutes.
For small production units (1 acre) about 50 leaves should be collected
for each sample; for larger units (5 acres) 150 leaves are adequate.
9.4 Evaluation of Sampled Leaves Leaves are easier to evaluate in
a comfortable, well-lighted place. They are examined one-by-one and
placed in groups according to the amount of disease damage. The
amount of damage is determined by comparing the leaf with a disease
damage key (Figure 7). Leaves should be placed into the class where
they fit best. For example, if a leaf has more than 1 percent leaf area
damaged (LAD) but not 10 percent, it belongs in the class for 5
percent LAD. When all leaves in the sample have been evaluated, the
number of leaves in each damage class (0, 1, 5, 10, 20, 40, or greater
than 40 percent LAD) are counted. The number of leaves in each
class is multiplied by that class value (see example, Figure 8). Leaves
in damage Class 7 (greater than 40 % LAD) are not commonly
encountered; a value of 70 % LAD can be assigned to these leaves.
Class totals are summed and divided by the total number of leaves
collected to provide an average percent LAD. Another useful statistic
is the percent of leaves that are infected. This value can be obtained
by summing the number of leaves in all classes (except 0's), dividing
this sum by the total number of collected leaves in the sample, and
multiplying by 100. An alternative system, that may be better for some
applications, is to use the subjective numerical damage classes 0
through 7 which correspond to 0, 1, 5, 10, 20, 40, and greater than 40
% LAD respectively. These classes are also shown on the disease
damage key (Figure 7). Average class values for sampled leaves can
be obtained with methods similar to those used for LAD data.
9.5 Records, Summaries, and Interpretation of Results Records
are most valuable to explain current observations but can be useful for
several years. Scouting data should be maintained for each unit along
with records of cultural inputs and activities and pesticide applications.
Fern growth, and yield data are also useful. Scouting data are easiest
to use when summarized graphically or on a scouting report (see
Figures 8, 9 and 10 for examples). Julian days or day-of-year are
convenient for plotting data or when computers or data loggers will be
involved. To monitor the progress of disease, or the effectiveness of a
control or management strategy, results presented in graphical form
(particularly as cumulative results) are most useful (Figure 10).
Comparisons should be carried out over a reasonably long period
(weeks). Effects from a particular fungicide application (or lack of one)
can usually be seen within one week, but generally within two. Yearly
summaries are valuable to see how weather affects disease, disease
control, and insect incidence. Computers are helpful for these tasks
but not essential.
Leaves collected during scouting are
evaluated to provide quantitative data
on anthracnose incidence and levels
of disease damage. These variables
are estimated by the percent of
sampled leaves that are infected and
the average percent of leaf area
damaged (LAD).
Scouting data are most useful when
presented in graphical form or in
scouting reports.
Yearly summaries, particularly when
in graphical form, are valuable for
understanding anthracnose and for
evaluating management programs.
PAGE 9 3
EVALUATING DISEASE MANAGEMENT
Disease foci, or hot spots, should be
marked or flagged and their location
recorded in order to avoid contact
with them and to help evaluate
supplemental control programs.
Locations of hot spots can often
reflect the probable method of
anthracnose introduction and spread.
Scouting for anthracnose can be
easily combined with scouting
activities for insects or inspecting for
cultural problems and pre-harvesting
information.
9.6 Mapping Disease Foci Disease foci (hot spots) may be
encountered during inspection or scouting. Foci should be well-
marked and their locations recorded. This is helpful to document new
occurrences of disease in a fernery and for planning and applying
rehabilitative treatments. Marking or flagging can help to avoid
unnecessary worker contact with foci and are useful when evaluating
the progress of disease control in foci or the effects of management
activities over time.
Locations of disease foci plotted on a map of the fernery can
sometimes be used to determine where the disease originally
appeared. Such maps can often suggest how the fungus was likely to
have been introduced. Locations where visitors, workers, or
equipment commonly enter the fernery, occurrences of irrigation or
chemigation malfunctions, and patterns of spray coverage and surface
water runoff are usually reflected by the distribution of disease damage
and foci. These locations become more evident after mapping them.
For example, a few small, well-defined, disease foci indicate a
relatively recent introduction. Numerous disease foci with diffuse
edges or large foci whose borders tend to overlap indicate that disease
has been present for some time and that extensive secondary spread
has occurred within the fernery.
9.7 Integration With Scouting For Other Pests Scouting for
anthracnose is compatible with monitoring other diseases such as
Cylindrocladium and Rhizoctonia and with detecting insect, cultural,
and nutritional problems. Insects or feeding damage can be observed
while scouting or evaluating leaf samples. Specific methods for the
Florida fern caterpillar are being developed. As a result of monitoring
fern anthracnose, large cost savings have been realized because
scouting activities have also confirmed that the fern caterpillar was not
present and no insecticides were required. Weekly sampling provides
an early and reliable warning of insect infestations. Unnecessary
sprays can be avoided, yet detection is early enough to effectively
control the caterpillars when required. We anticipate new
developments in the area of integrated scouting and pest management
since many procedures developed for other crops are easily
transportable to fern production.
PAGE 9-4
Evaluating Disease Management
Mature leaf
no disease damage
4-6 lesions
Class = 2
About 20% LAD
Class = 5
Correct sampling stage
(unfurled, light green)
No disease damage
Class = 0
About 5% LAD
Class = 3
About 40% LAD
Class = 6
Very few lesions
Class = 1
About 10% LAD
Class = 4
Greater than 40% LAD
Class = 7
PAGE 9 5
Figure 7. Disease damage key
EVALUATING DISEASE MANAGEMENT
LEATHERLEAF FERN ANTHRACNOSE
SCOUTING DATA RECORD FORM
LOCATION Shadehouse # 3
DATE 8/24/96
UNIT B
COMPILED BY: JS
Class 0 1 2 3 4 5 6 7 Totals
Number
Leavesin 108 27 9 5 2 0 0 0 151
class
Class x
Number of 0 27 18 15 8 0 0 0 68
leaves
Total for
Class x # of leaves = 68 = Average percent LAD 0.45
Total # leaves 151
Total # Leaves # Leaves in class 0 = (151 108) = 0.285
Total # leaves 151
0.285 x 100 = Percent leaves infected (28.5%)
Figure 8. Example work sheet for calculating average percent leaf area damaged
(LAD) and percent leaves infected.
LEATHERLEAF FERN SCOUTING REPORT
SITE: UNIT B, Seville DATE: July 9, 1996
Sampled Unit: New leaves, mid late expanded (Growth stage 5)
Random sampling throughout unit
Southeast Production
Unit
Number of
Leaves
Sampled
Percent With
Anthracnose
Damage
Average %
Leaf Area Damaged
151
52.31
0.85
Northeast Production
Unit
150
38.0
0.63
Insects No No
Notes Weeds a problem. No insects or insect feeding damage detected.
Broken irrigation riser in Northwest corner.
Figure 9. Sample scouting report which summarizes scouting results.
for a leatherleaf fern leaf sample.
PAGE 9-6
EVALUATING DISEASE MANAGEMENT
60
40 -
OL-
50
3-
2
1 -
0
50
100
150 200 250 300
JULIAN DAY 1996
100 150 200 250 300
JUUAN DAY 1996
Figure 10. Scouting data plotted against time for two production
units. Time is presented in Julian days (day of year for 1996).
PAGE 9-7
NORTHEAST
UNrr
EVALUATING DISEASE MANAGEMENT
SUMMARY OF SECTION 9 EVALUATING THE EFFECTIVENESS
OF DISEASE MANAGEMENT
* To manage fern anthracnose, you need to know what is happening
in the ferny. This requires periodic inspection and sampling.
* During scouting activities, take precautions to avoid introducing or
spreading anthracnose.
* Re-entry into pesticide-treated areas may require postponement or
wearing protective clothing.
* Scouting for anthracnose can detect the presence of disease at an
early stage and determine the extent of disease damage
already present.
* Scouting can assess the efficacy of management and control
strategies.
* Individual fern leaves are natural units for sampling and evaluation.
* The proportion of sampled leaves affected by disease and the extent
of damage are excellent indicators of disease incidence and
intensity.
* Weekly scouting results plotted against time are excellent for
evaluating disease control programs.
* Ferneries should be divided into a minimum number of scouting
units based upon factors such as age, disease damage,
cultural history, disease control programs, or harvesting
activities.
* One effective scouting method is to walk through and randomly
sample the entire production unit for anthracnose and look for
other problems such as insects, insect damage, malfunctioning
irrigation, and fertility problems.
* Approximately 150 leaves collected weekly from a 5-acre unit are
satisfactory to monitor disease progress and determine the
effectiveness of fungicide treatments.
* The short life cycle of the anthracnose fungus and continuous
production of new, susceptible, fern leaves makes weekly
sampling necessary.
* The fern leaf at Growth Stage 5 or 6 is the best sampling unit for
monitoring anthracnose.
* Sampling from this leaf population estimates the level of infection
and disease damage which occurred during the two-week
period just prior to sampling.
For random sampling, leaves are picked at random while walking in
a pattern likely to encounter representative portions of the
entire unit.
Sampling stations can also be used.
Disease damage is determined by comparing the leaf with a disease
damage key.
Another useful statistic is the percent of leaves that are infected.
PAGE 9-8
EVALUATING DISEASE MANAGEMENT
* Records are most valuable to explain current observations, but can
be useful for several years.
* Scouting data is easiest to use when summarized graphically or on a
scouting report. Comparisons should be carried out over a
reasonably long period (weeks).
* Effects of a particular fungicide application (or lack of one) can
usually be seen within one or two weeks.
* Yearly summaries are valuable to see how weather affects disease,
disease control, and insect incidence.
* Mapping and marking of foci are helpful to document new
occurrences of disease in a fernery and for planning and
applying rehabilitative treatments.
* Locations of disease foci plotted on a map can help determine where
the disease originally appeared.
* Scouting for anthracnose is compatible with monitoring other
diseases and with detecting insect, cultural, and nutritional
problems.
PAGE 9-9
SEASONAL MANAGEMENT
10.0 SEASONAL ASPECTS OF ANTHRACNOSE MANAGEMENT
10.1 Effect of Fern Growth Immature fern leaves are essential for
fern anthracnose to develop. Since new leaves are most abundant
during spring, summer, and early fall, these are the most critical
periods for anthracnose management. If anthracnose is present, new
leaves must be protected or very large populations of the anthracnose
pathogen can quickly result. During the winter and late fall, leaf
initiation rates are slowed and it is easier to keep leaves protected with
fungicide. However, fungicide programs should never be curtailed
completely. Neither fern growth nor disease development ceases in
the winter. They are just less apparent.
10.2 Seasonal Requirements and Management Throughout The
Year Anthracnose management is required throughout the year. It
is a serious mistake to discontinue exclusion precautions and
sanitation practices, cultural controls, or fungicide programs in the
winter, even though anthracnose can be much less apparent during
this season. Although, less active, the anthracnose pathogen can be
just as easily and effectively spread or introduced into a fernery in
winter as in summer particularly if wet conditions prevail.
The anthracnose pathogen and the disease are active all year in
Florida. During warm intervals in the winter season, fern anthracnose
can progress at rates similar to those observed in summer. During
these warm periods, temperatures and moisture are adequate for
disease development and the primary limiting factor is probably the
rate of leaf initiation by the fern. However, low leaf initiation rates
coupled with periodic interruptions to the life processes of the pathogen
caused by cold intervals drastically slow the overall long-term progress
of disease during the winter season. Clearly, the relative duration of
cold and warm periods are important, but unpredictable, and the
potential for serious disease damage is always present, even in winter.
This is why there is no justification for eliminating all fungicide
applications during the winter season. However, the intensity of
fungicide programs can often be reduced during the winter especially if
anthracnose is under control. Often, application intervals can be
extended. If anthracnose is not under acceptable control, winter is the
best time to continue fairly intensive fungicide applications and reduce
pathogen populations to numbers that will result in more manageable
disease levels when favorable conditions return. Scouting or
monitoring disease incidence and intensity is essential if you plan to
use this approach to anthracnose management.
Average temperatures and available
moisture change with the seasons.
This greatly affects fern growth and
anthracnose development rates.
Requirements and opportunities for
managing anthracnose change with
the seasons of the year in Florida.
Fungicide programs should not be
discontinued in the winter;
anthracnose is active throughout the
year. The potential for spread,
introduction, and serious disease
losses remains throughout the year.
Late fall and winter are the easiest
and best times to rehabilitate
severely-diseased ferneries.
PAGE 10- 1
SEASONAL MANAGEMENT
10.3 Best Times to Rehabilitate Damaged Ferneries The best
time to rehabilitate ferneries damaged by fern anthracnose is as soon
as possible after the disease has been detected. This should be done
in order to reduce opportunities for the production and spread of
secondary inoculum. However, cool, dry weather creates conditions
which are much less favorable for disease and a reduced leaf initiation
rate prevails, so late fall and winter are the easiest times to rehabilitate
badly damaged ferneries. Rehabilitation during fall or winter justifies
more intensive fungicide programs than normal seasonal maintenance
programs would require. Appropriate efforts and expenses will be
repaid through lower disease management costs in spring and
summer. Winter is also a convenient time to reduce pathogen
populations to numbers that are as low as possible. This approach
can greatly reduce anthracnose incidence and result in more
manageable disease levels when disease favorable conditions return in
the spring.
SUMMARY OF SECTION 10 SEASONAL ASPECTS OF
ANTHRACNOSE MANAGEMENT
* Immature fern leaves are essential for fern anthracnose
development.
* Since new leaves are most abundant during spring, summer, and
early fall, these are the most critical periods for anthracnose
management.
* During the winter and late fall, leaf initiation rates are slowed and it
is easier to keep leaves protected with fungicide sprays.
* Neither fern growth nor disease development ceases in the winter;
they are just less apparent; the potential for spread,
introduction, and serious disease losses is decreased, but not
eliminated.
* If anthracnose is present at acceptable levels, or apparently absent,
the intensity of fungicide programs can be decreased but not
discontinued.
* Fungicide application intervals can be extended during the winter if
anthracnose is under control.
* Late fall and winter are the best times to continue frequent fungicide
applications and reduce pathogen populations to numbers that
will result in more manageable disease levels when favorable
conditions return.
* Monitoring disease incidence and intensity throughout the year is
also essential if you plan to use this approach to anthracnose
management.
* Late fall and winter are the easiest and best times to rehabilitate
badly damaged ferneries.
PAGE 10-2
OPPORTUNITIES AND CHALLENGES
11.0 DISEASE MANAGEMENT: OPPORTUNITIES AND
CHALLENGES
11.1 Understanding the Problem To manage fern anthracnose, the
problem must first be defined and understood. Hopefully, this has
been provided. Then, the activities needed to manage anthracnose
need to be carried out at the appropriate times. Forethought and
planning are the keys to success. Anthracnose management is no
different than integrated pest management (IPM), integrated crop
management (ICM), or similar approaches; all are essentially
systematic approaches to solving a set of problems. Management of
fern anthracnose is fairly straight forward, but it must be well-integrated
with fern production and with the management of other fern pests.
In many crops, production methods evolve naturally over time, then an
intractable pest or problem appears that forever changes well-accepted
production methods. For leatherleaf fern, anthracnose is such a pest.
Present and traditional methods of fern culture are largely incompatible
with achieving and maintaining acceptable levels of fern anthracnose.
In fern production, all management decisions must consider the likely
consequences (or benefits) in regard to anthracnose as well as other
components of fern production. If you understand this, then you are
well on your way to successfully managing fern anthracnose and other
pests.
11.2 Obtaining the Information You Need Contact your Extension
Agent for the latest publications concerning fern anthracnose, current
fungicide recommendations, fungicides labeled for leatherleaf fern, and
suggested application programs. Product information and fungicide
vendors are other useful sources. Several sources of information have
been referenced in this manual. Most can be obtained through your
Extension Agent. Obtain and review the latest version of the Florida
Plant Disease Control Guide (Reference 4) which provides an
abundance of useful information on fungicides, fungicide application,
and principles of disease control.
11.3 Implementing the Program Get started today. Consider the
information presented in this manual when you make any decision or
undertake any production-related activity. Managers must make sure
that all employees understand the problem as well and that they are
adequately informed or supervised concerning activities that impact
anthracnose. Be aware that the activities of employees represent the
weakest link in anthracnose management. Here is where the best
intentions can fail because it is usually not managers but employees
who carry out activities that will have the most important consequences
for anthracnose management. Finally, begin periodic scouting now
The fern anthracnose problem can
only be solved by a systematic
approach. Initiate an anthracnose
management program now. Begin
scouting today.
PAGE 11-1
OPPORTUNITIES AND CHALLENGES
A major long-term goal of fern
anthracnose management is to
minimize fungicide use.
even if only in the simplest manner. You will be surprised at the
knowledge you will gain and how scouting data reinforces good
management decisions and quickly identifies poor ones.
11.4 Fern Anthracnose and Pesticide Use Initially, successful
management of fern anthracnose may rely heavily upon frequent and
sustained use of fungicide as well as special cultural and other
management practices which make control with fungicides feasible.
However, a major goal of disease management is to minimize
fungicide use. Once the disease is under control, the emphasis of fern
anthracnose management should shift to sanitation, disease exclusion
and avoidance, and the adoption of cultural practices that avoid and
minimize disease damage and spread. Fungicides should be applied
on an as-needed basis. Monitoring anthracnose will provide the
information needed to make these decisions.
Long-term use of fungicides at amounts and frequencies needed for
rehabilitation and to suppress or gain initial control of anthracnose are
not in the best interests of fern production, nor are they
environmentally acceptable over the long term, particularly in regard to
issues of soil accumulation and ground water contamination by
fungicides. Anthracnose management should neither rely on, nor plan
for the continued use of fungicide programs of the intensity required to
bring fern anthracnose under control. Fern growers should not lose
sight of this important management goal.
PAGE 11 -2
USEFUL REFERENCES
12.0 REFERENCES CITED
1. Leahy, R., T. Schubert, J. O. Strandberg, and D. A.
Norman. 1995. Anthracnose of leatherleaf fern. Florida
Division of Plant Industry, Plant Pathology Circular No.
372. 4 pages.
2. Stamps, R. H., McColley, D., Norman, D. and
Strandberg, J. 0. 1995. Results of leatherleaf
anthracnose survey. Cut Foliage Grower, University of
Florida Cooperative Extension Service. Vol 10, No.
9/10, September October, 1995. 7 p.
3. Poole, R. T., Conover, C. A., and Stamps, R. H. 1984.
Vase life of leatherleaf fern at various times of the year
and at various frond ages. Proc. Fla. State Hort. Soc.
97:266-269.
4. Simone, G., T. Kucharek, M. Elliott, and R. S. Mullin.
1994. 1994-95 Florida plant disease control guide.
University of Florida Cooperative Extension Service.
Publication SP-52. Volumes I and II, 489 p.
5. Stamps, R. H. 1995. Irrigation and Nutrient
Management Practices for Commercial Leatherleaf
Fern Production in Florida. University of Florida
Cooperative Extension Service Bulletin 300. 25 p.
6. Stamps, R. H. 1991. Cold Protection of Leatherleaf
Fern in Lake, Putnam, and Volusia Counties, Florida
(Spec. Pub. SJ 91-SP15, St. Johns River Water
Management District.)
7. Stamps, R. H. 1995. SI fungicide management
strategies minimize the risk of resistance. Cut Foliage
Research Note RH-95-D. Central Florida Research and
Education Center, University of Florida. 2 p.
8. Stamps, R. H. 1992. Commercial leatherleaf fern
culture in the United States of America. pp. 243-249.
In: Fern Horticulture: Past present and future
perspectives. The proceedings of the International
Symposium on the Cultivation and Propagation of
Pteridophytes, London England. Intercept, Ltd.,
Andover, UK.
9. Stamps, R. H., J. O. Strandberg, and G. W. Simone.
1995. Some general recommendations regarding the
PAGE 12 -1
USEFUL REFERENCES
prevention and management of anthracnose in
leatherleaf fern. Ornamental Outlook. Vol.4, No.1,
Pages 111-12.
10. Strandberg, J. 0. 1996. Pathogenicity of the
leatherleaf anthracnose fungus, Colletotrichum
acutatum on other wild and cultivated ferns. University
of Florida, Central Florida Research Report SAN 95-
05. 6 p.
11. Strandberg, J. 0. 1995. Efficacy of selected
fungicides for control of anthracnose in leatherleaf fern
A preliminary report. Cut Foliage Grower, University
of Florida Cooperative Extension Service. Vol 9, No.
11/12, November December, 1994.
12. Strandberg, J. 0. 1995. Evaluation of foliar fungicide
sprays for control of anthracnose in leatherleaf fern.
Cut Foliage Grower, University of Florida Cooperative
Extension Service. Vol. 10, No. 3/4, March April,
1995.
13. Strandberg, J. 0. 1996. Efficacy of some fungicides,
application strategies, and fungicide mixtures for
control of anthracnose of leatherleaf. University of
Florida, Central Florida Research Report SAN 97-04
(9/19/96), 7 p.
15. Tryon, R., and A. F. Tryon. 1982. Ferns and allied
plants with special reference to tropical America.
Springer-Verlag. New York.
PAGE 12-2
Florida Agricultural Experiment Station, Institute of Food and Agricultural Sciences, University of Florida, Richard L. Jones,
Dean for Research, publishes this information to further programs and related activities, available to all persons regardless
of race, color, age, sex, handicap or national origin. For information about alternate formats, contact the Educational Media
and Services Unit, University of Florida, PO Box 110810, Gainesville, FL 32611-0810. This information was published Febru-
ary 1997 as Bulletin (Tech.) 900 Florida Agricultural Experiment Station.
ISSN 0096 607X
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