HISTORIC NOTE

The publications in this collection do
not reflect current scientific knowledge
or recommendations. These texts
represent the historic publishing
record of the Institute for Food and
Agricultural Sciences and should be
used only to trace the historic work of
the Institute and its staff. Current IFAS
research may be found on the
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(EDIS)

site maintained by the Florida
Cooperative Extension Service.

Copyright 2005, Board of Trustees, University
of Florida

UNIVERSITY OF FLORIDA

IIUNIVERITY OF FLORIDA ||

AGRICULTURAL RESEARCH A
EDUCATION CENTER. LEESBU
BOX 388
TELEPHONE: 904/787-3423
(GAINESVILLE LINE 392-7272)

INSTITUTE OF FOOD AND AGRICULTURAL SCIENCES

HUME LIBRARY
ND I LEESBURG. FLORIDA 32749-0388

RG

SEP 17 1986

I.F.A.S. Univ. of Florida

BUNCH GRAPE FIELD DAY
July 8, 1986

FLORIDA

BUNCH GRAPES

another fruit crop

Leesburg AREC Research Report (LBG 86-11)
400 copies

COLLEGE OF AGRICULTURE

AGRICULTURAL EXPERIMENT STATION

COOPERATIVE EXTENSION SERVICE

SCHOOL OF FOREST RESOURCES AND CONSERVATION

CENTER FOR TROPICAL AGRICULTURE

The Institute of Food and Agricultural Sciences is an Equal Employment Opportunity Affirmative Action Employer authorized to provide research,
educational information and other services only to individuals and institutions that function without regard to race, color, sex, or national origin.

PROGRAM

Dr. Mary C. Halbrooks, Fruit Crops Department Moderator

9:00 Register (no cost), sample grape juices and buy your lunch ticket
to ($4.00/person). Maps to Leesburg Community Building will be
10:00 available.

9:30 Taste Test Panel of cultivars and experimental selections. Your
evaluations are used in the research program.

10:30 Taste test panel review by Dr. John Mortensen.

10:45 Tour of the research vineyard. Stops will include new walk-in cooler,
leafy cutting grafts, bunch grape varieties, vineyard sprayer in
operation, demonstration plot of gibberellin treatments on 'Orlando
Seedless', T-budding as a top-working technique, maxi-jet irrigation and
fungicide trials.

11:30 Travel to Leesburg Community Building, 209 E. Dixie Avenue.

Noon Catered lunch (Fried chicken, green beans, potatoes-n-cheese, rolls,
iced tea, apple cobbler).

12:55 Dr. G. W. Elmstrom, Center Director, AREC Leesburg.
Welcoming remarks.

1:00 Hon. Everett Kelly, State Representative, A Legislator's Perspective.

1:10 Dr. John Mortensen, AREC Leesburg, Historical Perspective of Florida
Viticulture.

1:20 Dr. Dennis Gray, AREC Leesburg, Grape Tissue Culture Research.

1:30 Dr. John Mortensen, Breeding Selections Now and for the Future.

1:40 Dr. Mary Halbrooks, Fruit Crops, Use of Gibberellic Acid on 'Orlando
Seedless' to Enhance Berry Size and Seedlessness.

1:50 Dr. Warren Adlerz, AREC Leesburg, Grape Root Borer Update.

2:00 Dr. Don Hopkins, AREC Leesburg, Grape Disease Control.

2:10 Dr. Bob Bates, Food Science and Human Nutrition, Processing
Opportunities for Florida Grapes.

2:20 Dr. Charles Sims, Food Science and Human Nutrition, Research Plans in
Processing, Enology and Postharvest Handling.

2:25 Closing Remarks.

2:30 Questions from the audience.

Grape Tissue Culture Research (D. J. Gray)

Tissue culture-related research is being conducted in the areas
of grape propagation, seedless cultivar development and somatic
cell genetic modification for disease resistance. Each of these
subjects is discussed below.

Rapid Micropropagation of Grape Cultivars

Tissue culture can be used to clonally propagate plants at a rate
far in excess of conventional nursery methods. The abundance of
surplus agricultural land in Central Florida in combination with
the unprecedented demand for 'Orlando Seedless' stock suggests an
immediate application for commercial tissue culture propagation.
During 1985, we tested the abilities of 35 grape species and
cultivars to be propagated in tissue culture (Proc. Fla. State
Hort. Soc. Vol. 98, in press). The procedure involved the
introduction of shoot apices into a specific tissue culture
regime. Within one month, each apex was induced to produce new
shoots. Although all could be propagated to a degree, some
cultivars responded better than others. Table 1 lists selected
cultivars that grow in Florida.

Table 1. Tissue culture propagation of grape cultivars.

Number of Shoots obtained/apex
Cultivars Apices Cultured after 1 month

'Black Spanish' 3 2
'Carlos' 53 5
'Daytona' 14 3
Dixie' 13 4
'Dog Ridge' 15 4
'Lake Emerald' 20 5
'Liberty' 21 6
'Norris' 15 4
'Orlando Seedless' 16 5
'Stover' 23 4
'Suwannee' 26 6

With this tissue culture system, each shoot can be either rooted
and established in soil or recultured to build up additional
propagation stocks. Considering a monthly proliferation rate of
5 shoots for 'Orlando Seedless' with an initial culture of 30
apices, over 2,300,000 shoots would be produced in 7 months by
serial reculture of apices.

The cost per plant from tissue culture would generally be less
than those produced by conventional methods, however, the plant
would be ungrafted and tend to be smaller. Interaction of
growers and nurserymen with commercial tissue culturists is
needed to determine optimum plant sizes, delivery methods, costs,
etc.

Accelerated Development of Seedless Cultivars

Conventional breeding of seedless grapes is complex and tedious
because crosses between seedless cultivars do not yield viable
seeds. To circumvent this problem, breeders now cross seeded
with seedless lines hoping to recover a seed that ultimately
produces a seedless vine. This process typically takes ten or
more years to accomplish. Using tissue culture, it is possible
to rescue the young seeds or ovules from seedless x seedless
crosses and promote the development of normal plants. In this
manner, the seedless trait is concentrated within one breeding
cycle. Plants are produced in a few months and then field
tested. Total development time is estimated to be four years.

In 1985, we cultured over 3,500 ovules and this resulted in 198,
potentially super-seedless, plants now growing in our vineyard.
The plants are the results of controlled pollinations between
various seedless lines (Table 2). Each plant is being evaluated
for resistance. Fruit quality data will become available in
1987.

Table 2. Progeny from controlled seedless pollinations conducted
during 1985.

Progeny
1 Ovules Embryos established
Parental Crosses cultured rescued in vineyard

Orlando Seedless x Arkansas 1105 885 52 36
Orlando Seedless x Flame Seedless 234 8 6
Orlando Seedless x Lakemont Seedless 604 27 21
Orlando Seedless x Missouri Red #2 497 24 14
Orlando Seedless x Thompson Seedless 399 29 19
Orlando Seedless x Orlando Seedless 320 52 43

Missouri Red #2 x Orlando Seedless 210 43 35
Missouri Red #2 x F9-68 234 20 17
Missouri Red #2 x Missouri Red #2 196 22 7

First cultivar listed in each cross was female parent.

For 1986, we cultured additional controlled pollinated lines,
including first attempts toward development of seedless muscadine
grapes. The tissue culture period for this year is now in
progress. Progeny from these crosses will be in pots and
evaluations will begin during Fall 1986.

Selection of Pierce's Disease Resistant Vinifera Cultivars

Pierce's disease (PD) is the major factor limiting the
establishment of high quality European and North American grape
varieties in the Southeast. All bunch grapes currently grown in
Florida are the product of crosses between these quality PD
susceptible grapes and low quality but resistant native grapes.
The breeding that this entails has taken a very long time because
repeated crossing and evaluation are needed to ultimately select
a vine that retains the quality of one parent with only the
regional adaptability and resistance of the other.

Plant tissue culture in combination with in vitro selection
offers the opportunity to circumvent the conventional approach by
producing resistant mutations directly from quality grape
varieties without use of native species. In this approach,
cultures containing large populations of spontaneously mutating
cells are challenged with PD toxin. Only those rare mutant cells
resistant to toxin are able to survive and grow. Eventually
cultures composed completely of resistant cells are produced. If
a high quality but susceptible variety is used as the culture
source, an identical, high quality but now resistant cultivar is
the result. Therefore, the best European and American cultivars
could potentially be expeditiously introduced into Florida
without conventional breeding.

Development of this system is one of the long term research goals
of our program. Several separate requirements must be met in
order to be successful. Basic research on PD toxin and methods
to standardize toxin extracts is urgently needed. Although grape
micropropagation as described above is routine, regeneration from
single cells is much more difficult. Thus far, we have obtained
regeneration via somatic embryogenesis from single cells of one
species, Vitis longii, as well as from several progeny of our
breeding program. Our next step will be to obtain embryogenesis
in a high quality vinifera cultivar that is adapted to Florida
climates but is still susceptible to PD. The best choice for
such a cultivar is 'Cabernet Sauvignon', a high quality red wine
variety which grows well in Florida but ultimately is lost to PD.
We have established 'Cabernet Sauvignon' in our greenhouse
cultivar collection and experimentation is underway.

Breeding Selections Now and For the Future (J. A. Mortensen)

Beginning with crosses between outstanding wild Florida bunch
grapes and cultivated grapes, a new race of grapes has been

created. The characteristics of this new race are varied
depending on cultivar, but have the following traits in common:

Older Races

New Race

Pierce's disease
Life span
Fruit production
Vine vigor
Fruit quality
Native parentage

susceptible
short (1-4 yrs.)
limited
weak to medium
good
no

The bunch grape breeding selections we are now
classified as those released since 1983, those
release, and those promising in vine and fruit
testing.

resistant
long (20-25 yrs.)
productive
vigorous
good
yes

looking at can be
nearing potential
but need further

Released Since 1983

Cultivar

Parentage

Conquistador
Suwannee
Daytona
Orlando Seedless

Color

Seedless

FL 43-47 x FL Ell-40 Purple
FL C5-50 x FL F8-35 Lt. Green
FL B3-90 x Exotic Pink
FL D4-176 x FL F9-68 Lt. Green

No
No
No
Yes

Nearing Release

Cultivar

FL H18-37
FL H17-22
FL BD12-49
FL E18-63
FL L9-10

Parentage

FL D6-148 x Cardinal
Norris x Schuyler
FL E9-48 x AR 1105
W1521 x Aurelia
FL 21C-31 x FL F5-8

Color

Seedless

Lt. Green
Purple
Lt. Green
Lt. Green
Lt. green

Further Testing Needed

Cultivar

NC 67B029-7
FL BN10-30
FL BN8-52
FL BN6-67
FL CD12-25
FL BD10-41
FL CB9-23

FL DN10-46
NC 74C040-20

Parentage

Color

Blue Lake x Hanepoot
FL E18-63 x Lakemont
FL E18-63 x Lakemont
FL DC1-39 x Himrod
FL 43-47 x Gamay
FL D5-166 x FL F9-68
FL 43-47 x Carolina
Blackrose
Stover x AR 1105
GA 7-2 x NC655073-10

Lt. Green
Lt. Green
Lt. Green
Lt. Green
Purple
Lt. Green
Purple

Lt. Green
Lt. Green

Seedless

No
Yes
Yes
No
No
No
No

Yes
No

While the above are at the forefront now, many others are under
observation and trial for possible use. New selections begin
fruiting every year for the first time (e.g., the new seedless

Date
Ripe

7/18
7/7
8/2
7/1

Date
Ripe

7/2
7/17
7/12
7/12
7/22

Date
Ripe

7/15
7/1
6/24
6/23
8/1
7/15
7/31

6/26
7/5

resistant x seedless susceptible crosses should begin fruiting in
1987). These offer possibility of being seedless cultivars
superior to Orlando Seedless. However, several years of testing
will be needed before we can be sure they are worthy of release
to growers.

Use of Gibberellic Acid on 'Orlando Seedless' to Enhance Berry
Size and Seedlessness (M. C. Halbrooks)

'Orlando Seedless' is the newest release from the bunch grape
breeding program at AREC-Leesburg. The fruit is light green in
color with high quality as a table grape. Two characteristics,
however, limit market acceptability of 'Orlando Seedless', (1)
small berry size and (2) occasional gritty seed traces.

Use of gibberellic acid (GA ) is a common practice in table grape
producing regions. Gibberellin is a naturally occurring compound
in the seed. Seedless grape varieties therefore have no
endogenous source of gibberellin. Activity of gibberellin is
variable throughout berry development and is responsible for many
different effects on physiological processes.

Application of GA causes increases in growth. This is a
physiological effect allowing cell walls to extend and take in
more water and solutes. Application of GA for this effect on
berries requires critical timing, the best3results associated
with applications made within 7-10 days of bloom. Availability
of water will determine whether the full potential effect of GA3
on berry size is realized.

The effect of gibberellin on seedlessness is not fully
understood. Perhaps the exogenous application simply inhibits
seed formation through a feed back inhibition effect. The
Japanese produce seedless grapes from normally seeded types by
applying GA pre-bloom. For enhanced seedlessness on a cultivar
such as 'Orlando' timing of application is critical within 1 to 2
days of full bloom. The effects of GA on berry size and
seedlessness are variable with concentration and are cultivar
specific.

Objectives of our study in 1985 were to determine the dates of
application (as defined by bloom stage) most responsive to
treatment and the lowest possible effective concentration which
could be used since GA3 is expensive.

Gibberellic acid applications were made at one of 4 stages of
bloom development. These included (a) full bloom, (b) 7 days
after full bloom (c) 14 days after full bloom, or (d) 21 days
after full bloom. Four concentrations of GA were tested at each
application date. These were (a) 38 ppm, (bP 75 ppm, (c) 150
ppm, or (d) 300 ppm.

Berry weights (Figure 1) increased between 38 and 300 ppm at all
stages of bloom development and were 109 137% of the berry
weight of controls. The best response was with 150 or 300 ppm
applied at 7 or 14 days after full bloom. Poor response was
obtained with treatments made 21 days after full bloom.

Seed weight (Figure 2) decreased markedly between 75 and 300 ppm
GA at 7 days after full bloom and were 16-40% of the seed weight
of controls. Little or no decrease in seed weight was obtained
with GA3 applications made at 14 or 21 days after full bloom.

In summation, greatest berry weights were associated with GA
applications of 150 or 300 ppm made at 7 or 14 days after fuhl
bloom. Smallest seed weights were associated with 75, 150, or
300 ppm GA3 treatments made at 7 days after full bloom. To
obtain maximum effects of GA with minimum dosage then would
require 150 ppm to be applied at 7 days after full bloom. These
results suggested further examination of (a) concentrations
between 150 and 200 ppm which may result in significant increases
in berry weight and, (b) application dates within 7-10 days after
full bloom which may further enhance seedlessness.

Commercial production practices in California include (a)
chemical thinning with GA applied at full bloom, (b) girdling to
increase berry size, and ?c) a second application of GA3 within
7-10 days after bloom to increase berry size. In 1986 we
incorporated these factors into a study which will provide data
on berry size, seed weight, cluster length, soluble solids and
other quality parameters. Preliminary results indicate that GA3
applications were very effective in producing marketable size
berries with complete seedlessness. Per acre yield of 'Orlando
Seedless' which averages 4.5 tons without GA3 treatment will be
at least doubled by such applications.

LiJ
016

LU 15

014

LL 13

S12

10

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48 41
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48 4
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38
75
150
300

+

- .1 A. '**.. ***--. I I ------ I I.... I --

14

21

DAYS AFTER CAPFALL

Fig. 1. Effect of concentration and application date of GA3 on berry
weight of 'Orlando Seedless'.

:t ~

i

1.

0
cO

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-) 0.1 I
_0- o.o
S0.10
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0 0.08
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0.04
0.03
0.02
0.01

+ y
r.1

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. 1-4i
* 4
.~'*4
4* 4
44

-~~~~~. 4 h-U I-

DAYS AFTER CAPFALL

Fig. 2. Effect of concentration and application date of GA3 on seed
weight of 'Orlando Seedless.

S Oppm
I 38
"^ 75
m 150
-i 300

+

44 94
49 49
49 449
44 944
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Insect Control on Florida Bunch Grapes (W. C. Adlerz)

Many insects can be found on bunch grapes in Florida. Some can
be severely damaging and control may be necessary. To keep
spraying to a minimum, growers may wish to become acquainted with
insects having the greatest damage potential, inspect vines
frequently, and spray only when necessary. This is a good
strategy, since preventive spraying will not be necessary in most
cases. Exceptions occur when growers experience annual problems
with grape seed chalcid, or if the grower adopts spraying to
control newly emerged root borer larvae in the fall as part of
the grape root borer control program.

Among the most persistent and damaging insects are the grape flea
beetle, grape leafhopper, and grape root borer.

These are discussed briefly.

Grape Flea Beetle

Grapevines are damaged by adult and by larval grape flea beetles.
Adult beetles are dark bluish-black and about 3/16 inch long.
They are usually the first insects of the growing season to
damage grapevines. Adult beetles feed on primary buds which then
cannot develop into primary canes, so crop yield is reduced.

Grape flea beetles breed in the vineyard, and females lay eggs on
various parts of the vine. Larvae are brown, spotted with black,
and about 1/4 inch long. They feed on the upper surface of
leaves and on developing flowers and buds, reducing yields.

Since both adults and larvae are easily seen vineyards should be
carefully monitored in the early season, paying special attention
first to cane and then to flower buds. Insecticides should be
applied when necessary.

Grape Leafhopper

Grape leafhoppers can be expected to infest vines each year.
Adult and immature insects feed on the undersides of leaves
causing pale feeding spots visible from above and even general
discoloration. Vine growth and sugar content of the grapes may
be reduced and seriously affected vines will be weakened.
Excreta from these insects may collect on the fruit which will
then be spotted and possibly covered with sooty mold.

Grape leafhopper adults are light colored, about 1/8 inch long
and very active. Immatures are very small, often difficult to
see, usually immobile, but can be provoked to activity by
touching.

An application of insecticides made prior to flowering and a
second 2-4 weeks after flowering will result in good leafhopper
control if one elects preventive spraying.

Grape Root Borer

Grape root borer may be the most serious threat to grapes in
Florida, having the potential to kill both bunch and muscadine
vines. Root borers have been found in most varieties of
grapevines in Florida, (Table 3). Larvae tunnel in the roots,
reducing root diameters and girdling even large roots. Large
larvae often make their way into the crown of the plant. Marked
reductions in vine vigor and yield is cause to suspect root borer
activity. Detection is by exposing part of the root system to
inspect for larvae or damaged roots.

Larvae remain in the soil for about 22 months before coming to
the surface to pupate. The adult moths are active and can be
seen in the vineyard in the daytime. Adults are brown wasplike
moths with yellow markings. Females lay eggs on a variety of
plant materials or on the ground. Newly hatched larvae tunnel
through the soil to the roots.

The only available chemical control method is spraying the ground
to create a chemical barrier to newly hatched larvae that are
attempting to penetrate the soil surface to the grapevine roots.
Larval control with this method has been found effective in
Florida. The approved insecticide for this is Lorsban, which
should be applied according to label directions. Do not apply
less than the 2 quarts of dilute spray per vine called for on the
label. A concentration of 4.5 pints of Lorsban 4E/100 gallons of
finished spray is effective. The Lorsban label limits
applications to one per season. The insecticide label is the law
regarding application.

In Central Florida, root borer moths are active from about
mid-August to mid-November. Peak moth flights are late September
to early October. The single application of barrier spray that
is allowed by law should be made around the first of October to
vines on which harvest has been completed. Applications cannot
be made later than 35 days before harvest.

In the Tallahassee area it has been determined that moth adults
are active from late July through the end of September, peaking
around the first of September. Late August to the first of
September would be good timing for the barrier spray. If this is
in the harvest period, however, it will be necessary to count
back 35 days from the first anticipated day of harvest to apply
the spray.

At this time, moth flight data have been compiled only for
Lakeland, Leesburg, and the Monticello-Tallahassee area. Short
distances between vineyards may result in large differences in
moth flight periods.

Other Insects or Damage Commonly Seen

Grape leaf folders, grape leaf skeletonizers, grape leaf miners,
grape phylloxera, grapevine aphids, and anomala beetles are
commonly seen in the vineyards.

All are considered minor pests that may not require control
efforts. Grape leaf folders and skeletonizers may be especially
abundant in the late summer and fall. Skeletonizers (brightly
colored yellow and black striped larvae feeding in groups) should
not be allowed to denude vines, so they should be sprayed if
necessary. If foliage disappears, remaining foliage is smeared
with black frass, and no insects are seen, look for anomala
beetles under vines, or look for insects eating foliage at night.

Table 3. Occurrence of grape root borers on various grapes in
the laboratory research planting and a commercial
vineyard: cast pupal skins at the soil surface.

Liberty (Lake Emerald)
Stover (Lake Emerald)
Blue Lake
Lake Emerald
Norris (Lake Emerald)
L4-33 (Dog Ridge)
Southland
Magnolia
Thomas
Redgate
Chief
Regale
Magoon
Tarheel
Welder
Watergate
Fry
Creek
Dixie
Dearing
Jumbo
US42-12B
Cowart
Noble
Hunt
Sugargate
Carlos
Higgins

Pupal skins per
Laboratory
1979 1980 1981

0.0
0.0
0.2
0.2
0.2
0.3
0.5
0.7
0.8
0.8
0.8
0.8
1.2
1.2
1.3
2.2
2.2
2.3
2.3
3.3
3.6
4.0

0.5
0.2
0.3
0.8
0.0
0.0
0.2
0.3
0.0
0.0
0.3
0.0
0.3
0.3
0.0
0.2
0.0
0.3
0.6
0.3
0.2
0.0

0.4
0.0
0.6
1.0
0.5
0.0
0.3
0.6
0.6
0.0
0.5
0.3
0.8
0.0
1.3
0.5
0.6
0.8
1.4
2.6
0.0
0.7

vine
Commercial2
1980 1981
0.2 0.5
0.4 1.0
0.4 1.7
0.8 0.4
1.2 1.0
2.3
0.6 0.4
0.6 0.5

0.3

1.4
2.6

2.6

0.4

4.0

3.4

2.5
2.7

0.4
0.6

1.2

2.2

3.6

1.2

1.7
2.3

1
2Average from 6 single-plant replications.
Average from 5 to 15 plants of each variety.

Insecticides for Bunch Grapes

When to spray

Insecticide

Bud break to flowering
(or later for beetle)

Pre-bloom and
2-4 weeks after bloom
Late April through
May, weekly
Post harvest

As needed

See discussion

Malathion or
Methoxychlor or
Carbaryl (Sevin)
Methoxychlor or
Carbaryl (Sevin)
Malathion

(as above)
Malathion
Methoxychlor
or

Carbaryl (Sevin)
Lorsban

Flea beetle
Leafhopper

Leafhopper

Seed
Chalcid1
Leafhopper
Aphids
Leafhoppers 2
Caterpillars
Fruit beetles
Root borer

Malathion

Carbaryl

Methoxychlor

Lorsban

1.5 pints 57% emulsifiable concentrate/100 gal.
water
1.5 teaspoons/gallon
Days before harvest 3

2 pounds 50% carbaryl wettable powder/100 gal.
water
2 tablespoons/gallon
Days before harvest 0

2 pounds 50% methoxychlor wettable powder/100 gal.
water
2 tablespoons/gallon
Days before harvest 14

Specific recommendation on label

Read the label it is the law.

When this insect is a problem preventive spraying will be
needed.
2
Grape leaf folder, leaf skeletonizer, hornworms, berry moths.

Grape Fungicide Test, 1986 (D. L. Hopkins)

Application Dates: April 11, 25, May 9, 23, June 6, and 23.

Pest

Grape Variety: Stover

~

Results to date:

2
Anthracnose rating
4/24 6/13 6/24

(A) Systhane + Dithane M-45 + Triton B-1956
(0.06 lb. ai + 3.0 lbs + 2.0 oz.)
(B) Systhane + Dithane M-45 + Triton B-1956
(0.12 lb. ai + 3.0 lbs. + 2.0 oz.)
(F) Captan + Benlate + Triton B-1956
(3.0 lbs. + 1.5 lbs. + 2.0 oz.)
(G) Captan + Spotless
(3.0 lbs. + 0.075 lb. ai)
(D) Dithane M-45 + Triton B-1956
(3.0 lbs. + 2.0 oz.)
(E) DPX-H6573
(0.03 lb. ai)
(C) Systhane + Triton B-1956
(0.12 lb. ai + 2.0 oz.)
(H) Unsprayed

1.0 a

1.1 a

0.3 a 0

0.2 a 0

1.0 a 0.1 a 0

1.1 a

0 a 0.1

1.0 a 0.2 a 0.3

1.0 a 0.6 a 0.5

1.1 a 0.2 a 1.2

1.4 a 1.4 b 3.1

Rate per acre is given.
Anthracnose was rated on a scale of 0-10.

Disease Control in Florida Grapes

Disease control is an absolute necessity to successful bunch
grape production in Florida. The most severe fungal disease is
anthracnose, which affects both foliage and fruit. There are 3
other fungal fruit rots black rot, ripe rot, and bitter rot -
that must be controlled. A number of leafspot diseases become
serious problems during late summer. These diseases must be
controlled to prevent premature defoliation in the fall, thus
assuring a stronger vine in dormancy and better yields in the
following year.

A long growing season, high temperatures, abundant rainfall, and
high humidity make bunch grape disease very difficult to control
in Florida. Therefore, a vigorous spray program must be started
in the spring when buds are 2-6 inches long and continued
throughout the season. Fungicides should be applied every 10-14
days until a week before harvest, and every 3-4 weeks from
harvest through November or until dormancy. Spray intervals
should be shortened during rainy weather, and may be lengthened
during dry seasons.

TreatmentI

Since muscadines are resistant to anthracnose, the first spray
can be delayed until just prior to bloom. As with bunch grapes,
fungicides should be applied every 2 weeks through harvest. One
or 2 postharvest applications are beneficial. The fungicides
recommended for grape disease control in Florida are listed in
the following table. A spreader-sticker may be included in the
spray. Please read the label for application instructions.
Remember, The Label is the Law.

Amt./l0 gal. Amt. per
Fungicide per acre gal.

Manzate D 1 1/2 lb. 1 1/2 TBS1
Dithane M-22 Special 1 1/2 lb. 1 1/2 TBS
Captan 2-4 lb. 2-4 TBS
Phaltan 2-4 lb. 2-4 TBS
Benlate 1-1 1/2 lb. 1-1 1/2 TBS

TBS = tablespoon

Since the activity of these fungicides against specific diseases
varies, it is advisable to use combinations of materials in a
grapevine disease control program. For example, Benlate may be
tank mixed with either Orthocide captain ) or Manzate D or Dithane
M-22 Special. Orthocide and Manzate D or Dithane M-22 is also an
effective tank mix.

Pierce's Disease of Grapevine

Pierce's disease (PD) is caused by a small, xylem-limited
bacteria. The symptoms include decline of vigor, marginal
necrosis of leaves, and often death of the plant. This disease
limits grape production in Florida. Both European type (Vitis
vinifera) and American type (V. labrusca) bunch grapes succumb to
PD.

Presently, the only effective control for PD is resistance. To
be productive in Florida, grapes must be resistant to PD. Most
varieties of muscadine grape have a high level of resistance, but
some are susceptible. 'Pride', 'Carlos', 'Lucida', and
'Scuppernong' are examples of muscadine varieties that are
susceptible to PD in Florida. Among bunch grapes, only varieties
developed at the AREC, Leesburg have enough resistance to PD to
be productive in Florida. These include 'Stover', 'Lake
Emerald', 'Blue Lake', 'Suwannee', 'Daytona', 'Conquistador', and
'Orlando Seedless'.

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