NEWARK, Del. - Once
soybeans begin active growth,
producers can expect to see many
different insects feeding on the
foliage. Green cloverworms,
Mexican bean beetles,
grasshoppers, Japanese beetles,
and bean leaf beetles all will attack
this crop.
It’s not unusual to find several of
these defoliators in most soybean
fields, says University of Delaware
extension pest management
specialist Joanne Whalen. So she
advises growers to use defoliation
estimates and population counts
when making control decisions.
Soybeans can generally tolerate
considerable amounts of
defoliation without yield loss. But
research has shown that tolerance
varies with the stage of plant
growth, plant vigor, and overall
growing conditions.
“Plants that are actively
growing can compensate for
foliage loss by adding new leaves
and increasing food production in
the lower leaves,” Whalen says.
“Beans under moisture stress
can’t compensate as well, so
defoliation thresholds should be
adjusted.”
She advises fanners to take care
to correctly estimate defoliation
during pod and seed development
stages, as severe yield reductions
can occur if defoliation exceeds 20
percent. Once plants have reached
maturity, leaf loss will no longer
affect yield.
Whalen offers the following life
histories so growers will know
when to scout for these defoliators.
• Green cloverworms: Over-
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Check soybeans for teaf feeding insects
wintering moths migrate nor
thward in late spring to lay their
eggs on clover and alfalfa. Larvae
begin to feed on soybeans in July
and peak larval feeding occurs in
early August. High populations of
this insect are generally controlled
by disease organisms.
Mexican bean beetles: Over
wintering adults move directly to
early planted soybeans where they
feed for a few days before laying
eggs. In Delaware, three
generations develop each year.
Economic infestations are most
likely to occur on early or late
planted soybeans.
Grasshoppers: Overwintering
eggs start to hatch in early April.
Immature and adult forms
generally move into soybean fields
in mid to late June. Economic
outbreaks are most likely to occur
in no-till soybeans, double cropped
beans, and in fields next to
recently harvested small grains.
Japanese beetles; Adults
emerge in late June and cause
most of their damage in early July.
Rapidly growing soybeans often
outgrow this damage.
Bean leaf beetles; Over
wintering adults enter fields when
soybeans emerge to feed and lay
eggs in the soil. First generation
adults emerge and feed in mid to
late July.
Start looking for defoliating
insects when soybean plants reach
the second trifoliate, and continue
scouting on a weekly basis until the
pod fill stage. Whalen says to
consider the level of defoliation,
stage of plant maturity, pest
population as well as the presence
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of natural control agents when in five locations throughout a field,
making a control decision. The following thresholds represent
Base defoliation estimates on a an insecticide is needed. (Please
random sample of 20 leaflets taken re f er to Graph A).
Plant Stage
Prebloom (first trifoliate to bloom)
Bloom (flower to pod set)
Pod-fill (small, fully formed beans)
Bean Maturity (bean hardening)
Since the decision to spray also -'insects found per 3 feet of row. Use
should be based on insect the following guidelines in corn
population levels, the specialist bination with defoliation
advises using a 3-foot by 3-foot thresholds in deciding whether or
shake cloth in the same five areas not to treat: (please refer to Graph
to sample and count the number of B).
Insect Species
Bean Leaf Beetles
Grasshoppers
Green Cloverworms
Japanese Beetles
Mexican Been Beetles
Spray sweet corn late
in day to protect bees
NEWARK, Del. - Sweet com
growers should wait until late in
the day to apply insecticides in
order to protect honey bees, ac
cording to recent research at the
University of Delaware
Agricultural Experiment Station.
Field studies by insect ecologist
Dr. Charles E. Mason show that
honey bees forage sweet com for
pollen primarily during the
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PETERMAN
FARM EQUIPMENT
717-249-5338
Chambersburg, PA
CLUGSTON
IMPLEMENTING.
717-263-4103
717-564-3031
Graph A
Graphß
No. of Insects/3 ft. of Row
from Prebloom to Pod-Fill Stage
48
12-18 (or 1 pegr sweep)
60 (wide row beans)
42 (narrow row beans)
20
20 or more (prebloom)
16 or more (bloom to pod set)
morning hours. So spraying in the
afternoon, evening or at night is
safer for them.
This information should make it
easier for commercial growers
who use integrated pest
management programs to time
pesticide applications, Mason
says. Sweet com plants don’t
benefit from bee pollination, but
honey bees collect com pollen for
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LCL CONSTRUCTION EQUIP.
SALE CO.
215-362-2510
Wilmington, DE
302-998-0128
Honey Grove. PA
NORMAN 0. CLARK
& SON INC.
717-734-3682
Martinsburg, PA
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814-793-2194
Lancaster Farming, Saturday, July 21,1984—D17
Defoliation Threshold
35 percent
20 percent
20 percent
35 percent
p
\
.ccessll
■aln
Myerstown. PA
SWOPE & BASHORE INC
717-933-4138
Slatlngton, PA
SCAT ENTERPRISES INC.
215-767-1711
Mill Hall. PA
DUNKLE& CRIES
717-726-3115
Rising Sun, Md.
AG-INDUSTRIAL
301-658-5568
Reminder; Delaware residents
can get further information on
inseason pest activity by calling
the University of Delaware’s crop
ri T be number is 1-800-
Fruit
to meet
LECK KILL A Twilight Fruit
Growers meeting sponsored by the
Schuylkill County Cooperative
Extension Service will be held at
Zimmerman Bros. Orchards,
Pitman and Felix Masser Or
chards, Leek Kill, on Tuesday at
6:30 p.m. The meeting will start at
the Zimmerman Bros, orchard.
Guest speakers will be James
Travis, Penn State Plant
Pathologist, giving an update on
the disease problems found in
orchards. Robert Crassweller,
Penn State Extension pomologist,
will discuss abnormal conditions
found in orchards throughout
Pennsylvania this year along with
tree training. For additional in
formation contact George P.
Perry, Jr., County Agent - Hor
ticulture, Schuylkill County
Cooperative Extension Service,
P.O. Box 250, Schuylkill Haven, PA
17972.
food in order to maintain colony
strength. Consumer demand for
insect free ears requires sweet
corn producers to spray plants
frequently.
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Tunkhannock, PA
BARTRON FARM SUPPLY
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Quarryville, PA
GRUMELLI’S
FARMSERV.
717-786-7318
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