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CENTRAL FLORIDA EXPERIMENT STATION
f" ""- Sanford, Florida
Mimeo Report CFES 67-6 July 11, 1967
CONTROL OF CORN INSECTS
Gerald L. Greene, Assistant Entomologist
The results shown in this report are not intended as insect control recom-
mendations, but are compiled to indicate the performance of the materials tested.
Sweet corn and field corn grown in Central Florida is subject to two insect
pests, the corn earworm (Heliothis zea) (Boddie) and budworms which are primarily
the fall armyworm (Spodoptera frugiperda) (J. E. Smith). Several control tests
were conducted during 1967 on these insects and the results are reported here.
BUDWORMS (Fall Armyworm)
Experiment I:- At Zellwood two applications of materials were made to three
row plots 50 feet long replicated four times. Treatments were made May 17 and
211 and damage readings were taken May 30, 1967. Approximately 80 gallons of water
per acre were applied at 250 psi through four nozzles per row directed at the bud
area of the plants. The sweet corn was planted April 18 and harvested as fresh
corn June 23.
The first five materials shown in Table 1 gave good fall armyworm control
and insecticides mixed with wheat bran bait appear to be promising preparations.
Combinations of DDT + Toxaphene or Parathion, which are commonly used com-
mercially, did not give satisfactory control of late instar worms.
Experiment II:- At Sanford sweet corn was planted April 3 and two appli-
cations were made, April 28, and May 9. Damage readings were taken May 17.
Materials were put on three row blocks 50 feet long in four replicates. Approxi-
mately 100 gallons of water per acre were applied through six nozzles per row
directed at the buds of the plants.
This experiment showed little effective control of the fall armyworm. Worms
were large, many in the 4th instar, and the corn was wilted during the day making
proper application extremely difficult. For these reasons this test must be
repeated and these data indicate only one thing, that UC 30045 is a promising
r^ ^'T--- T-;-'-------- ;--^--.
; AUG 14 1967
150 copies .
Table 1.- Experimental control of armyworms in the
Zellwood during the spring of 1967 i/
bud of sweet corn plants at
Per cent of stalks
Rank Material Rate Damaged 2/
GC 6506 4E
Sevin 80W +
DDT 2E /
DDT 2E 3
/The budworms were mostly Fall Armyworm larvae (Spodqptera frugiperda), but
some Beet Wrmyworm larvae (Spodoptera exigua) were present when the plants
-/Totals followed by the same letters) were not significantly different at the
5% level according to Duncan's multiple range test.
3/Several plants in these treatments showed effect of leaf burning.
Table 2. Experimental control of the fall armyworm in the bud of sweet corn
plants at Sanford during the spring of 1967.
Per cent of stalks
Rank 1/ Material Rate Damaged
1 UC 30045 1#A/A 17
2 UC 34096 1#A/A 63
3 Sevin 80W 2#A/A 67
4 Parathion 8E 0.25#A/A 79
5 Biotrol 2#/A 81
6 Toxaphene 8E 1.5#A/A 82
7 Thuricide SS 2 qt/A 84
8 N 2790 l#A/A 85
9 DDT 2E 1#A/A 90
10 Nia. 10242 2#A/A 93
11 Di-Syston 10G l#A/A 94
12 Check -- 98
STreatments Numbers 8, 10, and 11 were granular applications made April 3, the
day before planting the corn; and Numbers 3, and 5 were wheat bran baits
applied to the bud of the plants.
General Field Observations:- Budworm problems were common during 1967 on
field corn and sweet corn. Use of a preventative program of DDT + Toxaphene
gave good control when a strict schedule was adhered to, but this material
did not kill older larvae. In one field 40 pounds of DDT 10% + Toxaphene 2%
and in another field 40 pounds of DDT 10% + Toxaphene 2% + sulfur 40% gave no
observable control. Three applications of 40 pounds of Sevin 10% dust per
acre produced about 50% control. Use of cutworm bait consisting of wheat bran
+ Chlordane 2% + Toxaphene 2.4% applied to these fields gave some control.
Control was not complete due to heavy rains occurring soon after applications.
This combination did give good control in one corn field when applied before
the tassel stage as did applications of 25 pounds of wheat bran + Sevin 5%.
Experiment I:- Sweet corn at Zellwood was sprayed every 24 hours from May
31, just prior to silking, until all silks were brown on June 16. Approximately
120 gallons of water per acre were applied at 200 psi through six nozzles per
row directed at the ears. Records were taken June 20.
Seven treatments gave 98% or better worm free ears (Table 1) which is con-
sidered very good. Two formulations of Bacillus did not give satisfactory control.
This was probably due to an insufficient amount of the material being consumed to
cause death of the larvae before they entered the ear.
Experimental control of worms
the spring of 1967.
on sweet corn ears at Zellwood during
Rank Material Rate Per cent clean earsl
1/Totals followed by the same letters) were not significantly different at
the 5% level according to Duncan's multiple range test.
Experiment II:- High concentrate Sevin dust. A study of the effective-
ness of high concentrate dust for control of corn earworms was conducted on the
Zellwood muck farm operated by the Central Florida Experiment Station during
May 1967. Sevin dust 45% was applied by airplane at 4 pounds per acre. Dusting
began May 10 and continued every 24 hours through May 31, 1967. The first ap-
plication was applied prior to silking and the last on the morning of harvest.
All applications were made at approximately 6 A.M.
Results Earworm Readings
Sample Number of ears Per cent worm
date Treatment State of maturity sampled free
May 17 No treatment Harvestable 69 48
May 17 Sevin Silks white 100 100
May 23 Sevin Silks brown 50 100
May 23 No treatment Silks brown 10 80
May 29 Sevin First harvestable ears 100 87
May 31 Sevin Harvestable 200 93
May 31 No treatment Harvestable 30 77
June 1 /
June 3 Sevin Harvestable 50 78
June 7 Sevin Harvestable late variety 100 69
SA check of 140 ears from a commercial field adjoining the test area showed
98.5% worm free ears. This corn was treated daily with 40 pound of DDT 10%
+ Parathion 2%.
It appears from these samples that immature ears
them, but in a later sample where no control measures
small immature ears were infested. From this data we
dust did provide some control of earworms on immature
may not have earworms in
were used, over 90% of the
can say that 45% Sevin
The first sample with worms, May 29, was only 87% clean whereas on May 31,
93% of the ears were clean. This may be explained by the selection of early
maturing ears for the May 29 sample and breaking of ears at random for the May
31 sample. The early maturing ears were more heavily infested than were the ears
at the normal harvest period. The sample taken June 3 indicates a rapid break-
down of Sevin and a rapid increase of worms soon after applications were dis-
continued. Many of these worms were still quite small.
The May 17 and May 31 check samples suggest there were earworms in the area
and that 45% Sevin dust was controlling part of the earworm population.
The donation of all material and application costs by Union Carbide Corporation
in cooperation with Mr. Ralph Lawhorn their agricultural products representative
is greatfully acknowledged.
Experiment III:- At Sanford sweet corn was sprayed every 24 hours for ear-
worm control from May 25 to June 6 when insect readings were taken. Approxi-
mately 100 gallons of water per acre were applied at 250 psi through six nozzles
directed at the ears.
Experimental control of worms on sweet corn at Sanford during the
spring of 1967.
Material Rate Per cent clean ears
Gardona 0.5#A/A 67
Sevin 2.0#A/A 56
S2.0#A/A / 76
1/ Applied every 48 hours.
The low level of control cannot be fully explained, but the following
conditions were thought to be contributing factors:
1. Poor growth of the sweet corn due to extremely dry weather.
2. Heavy populations of budworms at the start of the spray program.
3. Isolation of the corn plots, there being very little sweet corn in
4. Poor spray coverage due to uneven height of plants and ears.
5. Uneven maturity of ears. There may have been some infested ears
before the first insecticide application.
Gardona and Sevin gave 100% and 99% worm free ears, respectively, in the
Zellwood trial, therefore they both appear to be satisfactory chemicals for
control of earworms on sweet corn.