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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
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site maintained by the Florida
Cooperative Extension Service.
Copyright 2005, Board of Trustees, University
cICUA 39 MA 17
I III. I' *II
FOIA COEAIVE' EXESO.EVC
GAINEVILLE FLORDA 3211
Soybean Insect Management
by John Strayer1 and Gerald Greene2
Several kinds of insects attack soybeans and can cause re-
duction in yield and grade. Some of these insects feed on foliage
while others attack the pods. At times soybeans can tolerate
considerable foliage damage without loss in yield; however,
protection against insect damage after blooming is most im-
portant for maximum yields. In order to carry out effective
insect management the grower must know the insects involved
and also recognize when insect numbers approach damaging lev-
els. It is very important for each grower to scout his fields and
apply insect control only when economic damage is probable. The
insect present must be known before the proper control program
can be chosen.
Velvetbean Caterpillar This is the most damaging foliage
feeder on soybeans in Florida. Caterpillar coloration is variable
although green is most common. Dark brown and black forms can
also be found. There are distinct yellow and white stripes run-
ning the length of the body and the head is usually yellow. These
caterpillars are very active and will spring from plants and wriggle
rapidly when disturbed. Individuals less than one half inch long
"loop" when they crawl and are often misidentified as soybean
loopers. The caterpillars less than one half inch long (first 3
stages) eat very little leaf area, less than one third of a leaf.
Figure 1. Average leaf area eaten by each caterpillar stage.
1Associate Entomologist, Florida Cooperative Extension Service
2Associate Entomologist, Florida Agricultural Experiment Stations
Worms over one half inch long (fourth, fifth ,and sixth stages)
inflict the major portion of damage since they can eat 31/2 average
soybean leaves. Figure 1 shows average leaf area consumed by
each caterpillar stage. The first three stages develop in about
four days in August. The fourth, fifth and sixth stages take about
10 days (Figure 2). This development time shows why you can
wait 2 or 3 days to control worms after small worms are found
in the field. Worms do not eat the plant overnight but require
several days to develop. The most important periods to watch
for velvetbean caterpillar damage are August and September.
This is the time when major damage to soybeans occur and when
control measures are justified.
0 2 4 6 8 10 12 14 16
Figure 2. Development time for various caterpillar stages.
Mexican Bean Beetle This colorful beetle has been one
of the more common soybean pests even though Florida seems to
be at its southern range. The oblong, yellow eggs are deposited
on the underside of the leaves by the adult females. The eggs
hatch into bright yellow larvae which have their back covered with
many spines. After growth is complete the larva cements itself to
the underside of a leaf and goes into a resting or pupal stage.
The adult emerges as a coppery-brown beetle with 16 black spots
on its back.
Both the larvae and adults feed on the under surface of the
leaves leaving the upper leaf surface intact. When the top surface
dries out it leaves a void between the veins and gives a skeleton-
ized appearance. When the infestation is heavy the pods and
stems can also be attacked.
Loopers These caterpillars are green and can have white
stripes and dark spots on their bodies. They can be easily iden-
tified from other caterpillars attacking soybeans by the fact that
they only have two pairs of fleshy prolegs on their abdomen.
Most of the other caterpillars associated with soybeans have
three or four pairs of prolegs. These worms move in the charac-
teristic looping or measuring fashion.
The adult moths deposit their eggs on leaves or other tender
plant parts at night. After hatching, the loopers feed on foliage
and produce a ragged appearance. Soybean looper feeding is simi-
lar to velvetbean caterpillar in amount of leaf area eaten per
caterpillar stage. Soybean loopers seem to prefer mature leaves
and often appear during the late growth stages of the plant.
Soybeans can withstand considerable damage of this type through
blooming without reducing the yield. A fungus disease often holds
loopers in check late in the season. Watch for mold encrusted
Corn Earworms This insect is a general feeder found on
crops such as corn, cotton, peanuts, tobacco and tomatoes, and
it can develop large infestations in soybeans at any time. These
worms can vary in color from light green or pink to nearly black,
but are generally lighter on their under surface and have alter-
nating light and dark stripes along the length of their bodies.
They have dark spines and small spots on their body which are
lacking on the other worm pests. When disturbed it will curl its
body up very tight. The tiny corn earworms can cause severe
damage to small seed pods before it is recognized. The small
worms are easier to control than the larger ones so it is important
to check the fields carefully. The corn earworm will also feed on
Stink Bugs These are shield-shaped green or brown bugs,
so named because of the offensive odor they produce. These
insects hatch from clusters of barrel-shaped eggs into nymphs,
which closely resemble adults. After a series of gradual changes
they become mature adults. Both the nymphs and adults have
piercing-sucking mouthparts and injury is done by puncturing the
pods and sucking fluid from the developing beans. This feeding
causes stained spots to appear on the beans which may lower the
grade and reduce seedling vigor.
Studies have shown that wild host plants such as wild dog-
wood, elder, peppervine, sumac, wild grape and black locust are
associated with the first generation stink bugs. They usually
appear in the soybean field during September when pods are
maturing. The borders of fields next to wild host plants should
be examined early to determine the abundance of stink bugs.
Other Soybean Insects
Fall Armyworm and Beet Armyworm Armyworms can
cause severe defoliation during the late summer or to very small
plants earlier in the season even though soybeans are not their
major food plant. The stripes and coloration of these worms are
highly variable; however, they can generally be identified by a
white inverted "Y" mark on the front of the head. The adult
moth lays eggs in a fuzzy cluster.
Lesser Cornstalk Borer This caterpillar is small and
slender with alternating green and brown bands on each body
segment. It lives in a silken tube just below the soil surface
and it bores into and tunnels up the stalk. When not feeding, it
stays in the silken tube. It can be a problem during dry seasons
when the plants are small. Plants suffering from lesser cornstalk
borer injury appear heavily wilted. There is not a good insecticide
control known and it is doubtful that routine control measures
would be profitable. Damage can be reduced significantly by
keeping land free of grass and weeds for several weeks prior to
planting. A suggested chemical control is 14 pounds of 14%
diazinon granules or 20 pounds of 10% parathion granules in a
6-8 inch band over the row when the plants are % to 1 inch tall.
Other insects sometimes associated with damage to soybeans
are cutworms, thrips, blister beetles, bean leaf beetles, bean leaf
rollers, green cloverworms and 3-cornered alfalfa hoppers. Infes-
tations of these insects are generally sporadic and in isolated
localities. Control measures for the major soybean pests should
be sufficient to control these minor pests if infestation poses an
Insect Disease and Beneficial Insects
There is a complex system of animal life present in the soy-
bean field. Numerous insects are parasites and/or predators of
the common soybean pests. Every effort should be made to help
conserve the beneficial species present. Since spray applications
also eliminate the beneficial species, it is important to be sure it
is necessary to spray a field. Once the beneficial species are elimi-
nated it is often necessary to apply additional treatments that
would otherwise be unnecessary.
At certain times insect diseases play an important part in
controlling some of the worms associated with soybeans. The
fungus Nomurea rileyi is commonly destructive to caterpillars
during September and October. The diseased worms appear with
a whitish mold-like growth. The presence of diseased caterpillars
usually signifies an end to worm infestations for the season; how-
ever, this is not a steadfast rule. If possible, hold treatments a
few days to determine if the disease is spreading.
In order to properly manage soybean insects, fields need to
be scouted to determine presence of damaging population levels.
Research has shown that one of the better ways to scout soybeans
is the shake cloth-beat method. Equipment necessary to do this
job includes a shake cloth, paper and pencil. The shake cloth
should be a white or off-white duck or muslin material measuring
45" x 48". Sew a 1/2" to 3%" hem on each 45" side. Use this hem
to insert a dowell or similar material to be used as handles on
which the cloth can be rolled or unrolled for easy handling
and row width adjustment (See Figures 3 and 4).
Fig. 3 Fig. 4
Enter the field and select the first sample site at random.
Standing between the rows, carefully place the shake cloth and
unroll it so that you cover the ground between the rows. While
kneeling down at the edge of the cloth extend your arm on the
outside of one of the rows and bend this "armful" of plant over
the cloth (this should normally be an average of 18"). Shake or
beat the bean foliage vigorously (Figure 5). Repeat this on the
other row. Count the caterpillars on the cloth. Some insect larvae
move rapidly so quickness is important. Record your counts.
You now have sampled 3 feet of row. Proceed to scout additional
sites until you have at least 5 samples for each 10 acres or until
you feel your samples are representative of the particular field
When sampling the insects also observe the percent leaf loss
that has been done by separating the plants to allow observation
of just one plant. Estimate the percent of leaf damage and record
this with your counts.
Know Caterpillar Characteristics
All of the caterpillars found in soybeans have specific char-
acteristics which enable identification of one from another. The
accompanying illustration shows details of the proleg characteris-
tics used to separate caterpillars.
How to Know When to Treat
Foliage Feeders Prior to full bloom soybeans can tolerate
33% defoliation without adverse effect on yield. Current research
indicates that treatment prior to full bloom should be made when
counts show 10 caterpillars 1" or longer per foot of row (30 per
shake). After full bloom when pods are filling leaf loss is more
critical. Data shows that an additional 10% foliage loss during
this period will adversely effect yields. Post bloom treatment
should be made when counts show 4 caterpillars 1/" or longer
per foot of row (12 per shake).
Pod Feeders Major pod feeders on soybeans are corn
earworms (podworm) and stink bugs. Pod feeding caterpillars
usually do not require treatment prior to bloom; however, corn
earworm infestations are closely aligned seasonly to blooming.
4 abdominal prolegs
3 abdominal prolegs
drops when disturbed
2 abdominal prolegs \
4 abdominal prolegs
rolls up into a ball
If field inspection shows leaf feeding by corn earworm imme-
diately preceding bloom, treatment may be necessary to prevent
later pod injury. During pod set and pod fill, treatment should
be made if counts show one corn earworm per foot of row (3 per
shake). Small corn earworms are hard to see so observe shakes
Stink bugs should be controlled when they average one per
3 feet of row (one per shake). If beans are for seed, one stink
bug per 6 feet of row justifies treatment. Stink bug infestations
are spotty, consequently more thorough scouting is necessary
to determine infestation levels. They are more common near field
borders and the wooded side of a field. Scout these areas carefully.
Treatment of an entire field for stink bugs may not be necessary.
Insecticides are poisonous to man and animals. Handle them
with care. Always read the insecticide label carefully and com-
pletely before opening the containers and observe all precautions.
Do not contaminate feed and water. Store insecticides in the
original labeled containers out of reach of children, pets and live-
stock and away from food or feed. Dispose of empty containers
promptly and safely.
The use of trade names is solely for the purpose of providing
specific information. It is not a guarantee or warranty of products
named and does not signify that they are approved to the exclu-
sion of others of suitable composition.
Material Amount* Restrictions
Velvetbean caterpillar carbaryl (Sevin) 0.25 to 0.75 lb.
Mexican bean beetle or active/A.
Green cloverworm methomyll 0.25 to 0.5 Ib. Do not apply methomyl within 14 days of har-
Corn earworm active/A. vest. Do not feed forage to livestock within 3
or days or hay within 7 days of last application.
toxaphene + methyl 1.5 +0.38 lb. Do not apply toxaphene within 21 days of har-
parathion active/A, vest. Do not feed treated plant materials to
livestock and poultry. Do not apply methyl
parathion within 20 days of harvest.
Soybean looper methomyll 0.25 to 0.5 lb
toxaphene + methyl 3.0 + 0.75 lb.
Bacillus thuringensis 0.5 to 1 lb./A.
Dipel WP 1 to 2 lbs./A.
Biotrol WP 1 to 2 qts./A.
POD FEEDERS methomyl1 0.25 to 0.5 lb
Corn earworm or active/A.
carbaryl (Sevin) 0.75 lb. active/A.
toxaphene + methyl 2.0 + 0.5 Ib.
Stink bug methyl parathion 0.5 lb. active/A. Do not apply methyl parathion within 20 days
or of harvest. Do not apply more than 2 applica-
tions per season.
methomyll 0.5 lb. active/A.
*Most dosages shown reflect active ingredient per acre. Formulations vary so be sure to use the amount of formulation necessary
to achieve recommended rates. Materials should be used in enough water to obtain thorough coverage. In dense soybeans 10-15
gallons of spray may be required. Pod feeders and velvetbean caterpillars feed in the tops of plants and are easier to kill with
low gallonages per acre. Follow label directions carefully.
1Methomyl = Lannate or Nudrin.
This public document was promulgated at an
annual cost of $601.17, or 8 cents per copy to
inform grower on pests of Soybeans.
COOPERATIVE EXTENSION WORK IN AGRICULTURE AND HOME ECONOMICS
(Acts of May 8 and June 30, 1914)
Cooperative Extension Service, IFAS. University of Florida
and United States Department of Agrculture. Cooperating
Joe N. Busby. Dean