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 This year’s appearance is earlier and in higher numbers, says
Nick Seiter, University of Illinois Extension field crops
entomologist. In addition to costly attack on alfalfa, pastures,
soybeans, corn, and small grains, the larvae of the moth are
infesting lawns and gardens.
Fall armyworms (Spodoptera frugiperda) can be found in the
Midwest nearly every year, but this year, multiple generations
of fall armyworms in southern Florida, southern Texas, and
Central and South America created a larger than normal
population of moths that moved to Midwestern states in late
summer, says Katie Parker, Illinois Extension local foods small
farms educator. The moths lay eggs which then develop into the
caterpillar larva that feed on crops, gardens, and lawns.
The caterpillars may appear green, brown, or black in color,
with white to yellow lines running along its back from head to
tail and an inverted “Y” between the eyes. Four black spots form
a square near the top back of the caterpillar. Caterpillars
begin at less than 1/8 inch and can quickly grow to 1.5 inches
after two weeks of feeding.
“With a large appetite and their habit of ‘marching’ in large
numbers, fall armyworms can do some damage in just a few days,”
Parker says.
After feeding, caterpillars tunnel about one inch into the soil
and enter the pupal stage from which a moth emerges after about
10 days, and the cycle repeats.
Moths are grey with a pattern of light and dark areas and a
wingspan of about 1.5 inches. Moths are more active at night,
feeding on nectar and depositing eggs.
A female moth can deposit up to 2,000 eggs with four to five
generations per year. Armyworms overwinter in the south.
Southern populations increase in early spring with future
generations moving north as the season progresses.
Illinois Extension horticulture educator Kelly Allsup recommends
homeowners soak dead lawn spots with soap and water.
“Add one tablespoon of liquid dish soap to one
gallon of water and pour over one square foot of grass,” Allsup
instructs. “Armyworms crawl to the surface within seconds. Even
two or three caterpillars can do substantial damage.”
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This year’s damage is likely due to our wet and cool
growing conditions, Allsup says. Severe cases may need to be treated
with insecticides to control the caterpillars. One should also apply
additional water to lawns to force the regrowth. Fall armyworm
larvae are controlled by the same insecticides used to control sod
webworms.
Damage to corn can occur as ragged-edged holes on leaves, tassels,
or ears. Caterpillars will also feed on the kernels of the ear.
“In turf, hayfields, or pasture, the damage often appears as brown
or burned out patches and can often be confused with drought
damage,” says Parker. “Scouting in the cool part of the day when the
caterpillars are actively feeding will allow you to determine the
size and number of fall armyworms to help decide control
strategies.”
Fall armyworm infestation is best controlled when caterpillars are ½
inch or smaller. If pyrethroid insecticides are used, make
applications early in the morning or later in the evening when
larvae are most active.
“Control failure with the use of pyrethroids has been reported in
the southern U.S. this year, and a few similar reports have come in
from Illinois,” Seiter says. “Individuals should consider
alternatives to pyrethroids if an application is warranted, though
these alternatives often come with an increased control cost.”
[SOURCES: Kelly Allsup, Illinois
Extension Horticulture Educator; Katie Parker, Illinois Extension
Local Foods Small Farms Educator; Nick Seiter, Illinois Extension
Field Crops Entomologist
WRITER: Judy Mae Bingman, Illinois Extension Interim Director of
Communications]
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