90o-
Late Planting Increases Fall Armyworm Damage
and
Reduces Yields in Tropical Corn
Central Science
Library
MAY 29 1990
University of Florida
I.D. TEARE, D.L. WRIGHT, and R.K. SPRENKEL
I.D. Teare, D.L. Wright, and R.K. Sprenkel, North Florida Res. and Educ.
Ctr. Quincy, FL 32351 (Dept. of Agronomy and Dept of Entomology and
Nematology, Institute of Food Sci., Univ. of Florida, Gainesville,
Florida 32611). Research Report NF-90-7.
INTRODUCTION
Farmers in the Southeast became interested in tropical corn [Zea
mays (L.)] in 1984 and planted about 5,000 A predominately Pioneer Brand
X-304C hybrid [coded X-304C]. By 1988, plantings had increased to about
10,000 A with good yields and in 1989 approximately 40,000 A were sown
to tropical corn. A moderate energy input system for tropical corn was
described by Teare, et al.(1989) based on four years research growing
X-304C when planted after winter wheat [Triticum aestivum (L.)]
(harvested around 24 May each year).
Overman and Gallaher (1989) conducted a date of planting study in
1988, where X-304C was grown in a high energy input system (no-till
planting at 34,400 plants/A, 270 lb N/A and irrigation) with three
planting dates (Mar, May, Aug). These authors reported yields of 150,
114, 78 bu/A for the three respective planting times and attributed
yield reduction to differences in temperature and daylength. Increased
pest problems were only mentioned. Bustillo and Gallaher (1989) state
"insect control needs further research [ on tropical corn ], to
determine the most effective and economical control program".
Experience in South America (J.E. Funderburk, 1988, personal
communication) indicated that IPM practices must be adhered to for
control of lesser cornstalk borer [Elasmopalpus lignosellus (Zeller)]
and fall armyworm [Spodoptera frugiperda (J.E. Smith)]. Few insect or
disease problems were experienced during 1985 to 1988, but the 1989
season was different.
Fall armyworm is a polyphagous, highly mobile insect that normally
arrives in North Florida by late-May. The population probably
2
originates each spring from continuous breeding populations in southern
latitudes (Barfield, et al.,1980). The erratic occurrence of fall
armyworm "outbreak years" and irregular distribution of heavy
infestations indicate that fall armyworm is a "boom or bust" pest. The
last "boom" year in the southeastern US was in 1977. Fall armyworm
larve developing on corn usually has six larval instars requiring a
period of 21 days. However, the life cycle is temperature dependent and
can range from 66 to 18 days at temperatures of 64 to 950F (Barfield et
al.,1978) .
Fall armyworm eggs laid on leaves in the whorl, generally escape
most natural predators, but egg masses laid after the tassel has emerged
are subject to greater predation (Martin et al.,1979). Natural enemies
have been observed to move sequentially through crops coupled by pest
flows and reduce population densities of fall armyworm in a very short
period (Martin et al.,1979).
Many practices are employed to plant, maintain, and harvest any
crop. Pest injury avoided by producing a crop at times when pest
populations are in nondamaging stages or at low population levels is
recognized (Herzog and Funderburk, 1986).
Our experiences in 1989 with tropical corn indicates a cultural
practice that improves the wheat-tropical corn doublecrop system
proposed by Teare et al. (1989) in relation to planting and fall
armyworm. The objective of this note is to document our observations
during 1989 on the effect of early and late planting on the
susceptibility of X-304C to fall armyworm and to suggest a planting
window after wheat harvest (24 May) where tropical corn seems to escape
the fall armyworm in a production environment.
3
MATERIALS AND METHODS
The fall armyworm observations reported in 1989 are from an on-going
tropical corn research program at the North Florida Research and
Education Center (NFREC) and surrounding tropical corn fields in Gadsden
county. The soils are a Norfolk sandy loam soil [fine-loamy, siliceous,
thermic, Typic Kandiudult]. All plantings were grown under the moderate
energy input system: no-till planting at a plant population of 18,000
plants/A 120 lb N/A [20 Ib/A as starter fertilizer at planting and 100
Ib/A when the corn was 12 inchs tall (approximately 31 days after
planting)], and no irrigation. The major difference from previous years
was rainfall, date of planting, and incidence of fall armyworm. Rainfall
data was collected at the NFREC weather station located approximately
200 to 800 yd from the tropical corn experiments. The early planted
experiment at the NFREC was planted 26 May 1989 to X-304C (four
replications in a randomized block design). The 1989 early planted
farmer field was planted to X-304C4 June eight miles west of Quincy.
The excessive rainfall from 21 May to 27 June delayed other tropical
corn plantings and flooded poorly drained areas. About half of the
early planted farmer field was not harvested because of excessive
soil-water causing oxygen stress in tropical corn. Only the yield of
the well-drained area is given. The 1989 late planted (29 June) study
was a tropical corn hybrid yield trial (four replications in a
randomized block design) containing X-304C and 15 other tropical corn
hybrids (Table 1). Grain yields were corrected to 15.5 % moisture
content.
RESULTS AND DISCUSSION
Excessive rainfall, delayed planting, and fall armyworm injury were
the major differences that we observed between the years of 1989 and
1985 through 1988. Rainfall from 21 May to 27 June 1989 was 20 inchs.
Rainfall during the tropical corn growing season of 1989 can be compared
with the rainfall for 1988 (Fig. 1). Only two fields of X-304C were
planted early in North Florida that we knew of, the rest, including the
tropical corn hybrid yield trial, were delayed until after 27 June.
The yield of the early planted tropical corn in 1989 was 61 bu/A at
NFREC and 65 bu/A in the farmers field compared to 94 bu/A yield average
for 1986, 1987, and 1988 at NFREC. Fall armyworm damage in the 1989
early planted X-304C was only noticeable on leaves about the same as
observed in 1985 to 1988. The 1989 late planted, fall armyworm infested
X-304C (planted 29 June) yielded 42 bu/A. Therefore, we have suggested
a window between 24 May and 10 June where fall armyworm damage is at a
low risk.
Under severe infestations as observed in 1989 late planted tropical
corn, the fall armyworm will skeletonize leaves in early instars or
produce ragged holes in later instars and eat the tassels and silks. We
have not observed much fall armyworm damage on the ears or stems of the
ears of X-304C, but grain fails to develop from lack of pollination.
Percent tasseling and silking curves for early planted X-304C in
relation to day of year for 1988 show little observable fall armyworm
damage, but percent tasseling and silking curves for late planted X-304C
in 1989 show extensive fall armyworm damage. The 1989 change in
tasseling pattern was observed on 240 day of year (28 Aug) when fall
armyworm consumption of tassels made it appear that tasseling had
5
ceased, followed by a slight increase and then a negative slope at 250
day of year (7 Sept). The consumption of silks in 1989 reduced the
silking slope at 244 day of year and it became negative after 250 day of
year. This indicates that fall armyworm populations were at their
highest levels during tasseling and silking. A very susceptable stage
of growth for any corn in relation to grain yield.
A late planted hybrid tropical corn yield trial with 16 hybrid
entries was conducted for the first time in 1989 and the effects of fall
armyworm infestation are shown in relation to mean yield and standard
error of the treatment mean in Table 1.
ACKNOWLEDGEMENT
Our thanks to E. Brown, Agricultural Technician IV and B.T. Kidd,
Biological Scientist II; North Fla. Res. and Educ. Ctr. Univ. of Fla.,
Quincy, FL; for data illustration and for plot preparation and
management.
REFERENCES
Barfield, C.S., E.R. Mitchell, and S.L. Poe. 1978. A temperature
dependent model for fall armyworm development. Ann. Entomol. Soc.
Am. 71: 70-74.
Barfield,C.S., J.L. Stimac, and M.A. Keller. 1980. State-of-the-art for
predicting damaging infestations of fall armyworm. Fla. Entomol.
63:364-375.
Bustillo, J.J., and R.N. Gallaher. 1989. Dry matter Partitioning in
No-tillage Tropical Corn in Florida. p.40-42. In I.D. Teare, E.
Brown, and C.A. Trimble (ed.) 1989 Southern Conservation Tillage
Conference. SB 89-1. Tallahassee, FL. 12-13 July, 1989. Univ. of
Fla., North Fla. Res. and Educ. Ctr., Quincy, FL 32351.
6
Herzog, D.G.,and J.E. Funderburk. 1986. Ecological bases for habitat
management and pest cultural control. p.217-250. In M. Kogan (ed.)
Ecological theory and integrated pest management practice. John
Wiley & Sons. New York, NY.
Overman, D.L., and R.N. Gallaher. 1989. Growth and Partitioning of Dry
Matter Between Temperate and Tropical Corn. p.38-40. In I.D. Teare,
E. Brown, and C.A. Trimble (ed.) 1989 Southern Conservation Tillage
Conference. SB 89-1. Tallahassee, FL. 12-13 July, 1989. Univ. Of
Fla., North Fla. Res. and Educ. Ctr., Quincy, FL 32351.
Martin, P.B., P.A. Goodman, and F.A. Marshall. 1979. Integrated
management of insects of pastures and forages in the Coastal Plain
of Georgia. Dept. of Entomol. and Fisheries Series 78: D.1-D.329.
Teare, I.D., D.L. Wright, and D.J. Zimet. 1989. Four years experience
with tropical corn in a doublecrop system. Univ. of Fla., North
Fla. Res. and Educ. Ctr., Quincy, FL. Res. Rep. NF-89-4.
Table 1. Hybrid tropical corn yields (bu/A) and standard error of the hybrid
in relation to brand and ranked by hybrid within brands during 1989 when the
hybrid tropical corn yield trial was late planted (June 29) and with severe
fall armyworm infestation in a moderate energy-input system.
Replications
Brand
Pioneer
DeKalb
Cargill
Hybrid
X304C
XCJ66
326
3210
3230
3212
XCE72
X8965
XCH53
6875
3238
B840
XL678C
XL604
C-343
C-381
77.9
70.5
14.4
23.1
36.6
33.8
21.7
27.0
19.5
19.9
21.3
23.9
36.5
27.6
41.1
31.3
31.6
24.9
18.7
8.4
24.5
6.7
20.6
11.8
2.7
3.0
4.6
34.6
25.4
6.1
17.2
14.2
28.0
36.4
25.8
24.0
2.5
3.0
0.9
0.6
22.7
9.9
3.6
29.1
20.2
16.8
16.2
20.9
30.5
13.1
22.0
23.3
1.3
19.7
3.2
7.1
0.4
1.6
0.1
22.0
25.0
7.6
30.7
4.0
42.0
36.2
20.2
19.7
16.2
15.8
11.6
11.6
11.3
8.6
7.4
27.4
26.7
14.5
26.3
17.6
S. E.
12.0
12.4
2.4
3.8
8.6
7.0
5.5
5.6
5.7
4.2
4.7
2.8
3.5
5.0
5.9
5.7
Grain yields corrected to 15 % moisture content.
1 1988
,I, I 1
,1t
140 150 160 170 180 190 200 210 220 230 240 250 260 270 280 290 300 310
-j
...J
S 7
LL 1989
Z
< 6
0: 0
z-
1-4
Z Z) >
r, I I
2 -
1
140 150 160 170 180 190 200 210 220 230 240 250 260 270 280 290 300 310
DAY OF YEAR
Figure 1. Rainfall, planting date, 50% tasseling, and harvest date
during 1989 and 1988 tropical corn growing seasons. Days of year
reported in days Julian.
5 -
. ,1
I Ij
I00
80
60
0 0 . . .. . ... ... ... ... ... ... ... ....
s o.8 ... 11- 1 .................... ................... ........ .......-- -- -- ...................
6 0 ................................................. .............. ....................... .....- .-- - ..................
4 0 ...................................... ... ... ..... .............. .................... ......-- -
lI I f I II I 'l
223 229 236
247
253
223 229 235 241 247 253
DAY OF YEAR
Figure 2. Comparison of tasseling and silking for 1989 in relation to 1988.
Negative slope after 250 days Julian (7 Sept) indicated time of severe fall
armyworm damage in 1989.
n -''L
I t I I #I I I I I 1 I I !
1988
1989
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