IPM, Cornell on front lines of armyworm invasion
By HEATHER SWANSON firstname.lastname@example.org | Published here with permission of the Finger Lakes Times
GENEVA — An ill wind has blown an unwelcome infestation of pests into the
A widespread infestation of true armyworms has blanketed New York state,
with known cases throughout the region.
The insects make sporadic appearances in the area. The last infestation
was a few years ago, but none as severe as this, said Mike Stanyard, an
entomologist and Cornell Cooperative Extension's Western New York area
field crops specialist.
"We have never seen something this widespread across the state," he said,
noting he has received dozens of calls from concerned farmers and spent
hours in the field assessing the situation.
The true armyworm is, in fact, a caterpillar, explained Keith Waldron,
field crop Integrated Pest Management coordinator at the Geneva IPM.
Waldron said the name is something of a misnomer, although the pests do
move in unison, much like an army.
While the caterpillars will soon become moths, in the interim they consume
field crops, grass and other plants.
Because the insects do not winter here, Stanyard believes the moths
traveled north by way of a storm front, possibly arriving with the flux of
Red Admiral butterflies that passed through the region in early May. While
the colorful butterflies created a stir, the moths are nocturnal and
likely went unnoticed, Stanyard explained.
The early spring is also to blame, he said, saying the moths were able to
build up in the south earlier than they typically would.
The crops and plants at most risk include grass or mostly grass hayfields
and pastures; corn fields that were late planted into grass fields;
no-till or reduced tillage fields; corn planted into small grain
(especially rye grass) cover crops; and corn fields with grassy weed
pressure. Small grains like wheat and oats are at risk, too, as are golf
courses and lawns. The armyworms will eat bean, cabbage, carrot, onion,
pea, pepper and radish leaves as well.
Cornfields should be monitored most closely now, Stanyard said. He added
that hay yet to be harvested has largely been ruined, and wheat is nearing
"Walk the edge of your cornfield," he advised.
Waldron encouraged people to look for the pest in the early morning and
evening — that's when they're most active.
True armyworm larvae appear smooth, cylindrical and pale green to brownish
in color when they are small. Mature larvae are smooth and marked with two
orange, white-bordered stripes on each side.
Larvae range in size from an eighth of an inch when they first hatch to 1
1/2 inches long at the end of three weeks. Their appetite increases with
In addition to looking for the insects, farmers should be wary of the
damage they cause, Waldron said.
"I'd be looking for signs of feeding on the grass," he advised. "I'd be
looking on the ground underneath some of the litter and debris that might
be on the ground."
"It looks like the yard is moving," said Carol Harris, who lives on a
Yellow Tavern Road farm in Fayette with her husband, Allen.
The armyworms targeted the Harris' fields first, then moved into the yard.
"It looks like it's liquid — that's how many of them there are," Carol
"When they move into a lawn they really can decimate it," added Jennifer
Grant, co-director of the Geneva IPM and Community IPM coordinator. "The
weeds are left standing."
Measures homeowners can take to control the pests on lawns are not the
same as the steps farmers can take in fields, Grant cautioned. Pesticides
must be specifically designed for lawn use. Additionally, those a
homeowner can apply differ from those a professional can.
"This is a situation where I think it's a good idea to hire a
professional," she said.
Should homeowners choose not to apply pesticides, Grant said the grass
will return but has to be watered to prevent sun damage that could kill
"In most cases, I expect it to come back eventually," she said, adding
that applying additional grass seed later in the season may be necessary
Mark Lott, a Seneca Falls farmer, has found armyworms on his County House
Road property and has been assisting other farmers in the area in spraying
for the pests.
"If you don't treat it, it can wipe the crop out," he said.
Lott said heavy infestations can often be spotted right away.
"You stand back in some wheat crops and you'll see them without even
bending over to look for them," he said.
Hoards of the insects will cross roads to reach neighboring fields.
Though the armyworm would typically trouble farmers for only about three
weeks before transforming into moths, that appears unlikely this time,
Stanyard said. The reason: Small, three-quarters-of-an-inch armyworms are
in the fields with half-inch armyworms, indicating staggered hatching
"This is going to go on the rest of the month," Stanyard predicted.
Natural parasites and pathogens may prove a saving grace, though. The
armyworms are typically targeted by a parasitic fly that kills them, as
well as a viral infection that could wipe them out.
"Those do have a tendency to come to our assistance," Waldron agreed.
Signs of the fly have yet to appear, but Stanyard believes the pathogen
may have arrived. Samples were sent to Cornell University for
It is also possible a second generation of the armyworm will make an
appearance sometime in July. Although second generations are typically not
problematic, Stanyard believes that may not be the case this time because
of the extent of the current infestation.
GENEVA — Extension guidelines from throughout the United States
recommend that IPM thresholds should be met before applying an
• Seedling-stage corn should be treated when 25 percent or more of the
seedling plants are damaged and larvae are still present.
• For whorl-stage corn, apply an insecticide only if most plants show
damage and about three larvae per plant are found. Control can be
challenging if caterpillars are greater than 1 inch long and near the
end of the feeding frenzy of the larva stage.
• In wheat fields, farmers should look for five or more larvae per
square foot and larvae less than 1 1/4 inches long and not
parasitized. Watch for flag-leaf reduction or if grain heads are
• In pastures, insecticide treatments can be justified when four or
more non-parasitized, half-grown or larger larvae are present per
Chemical control through the use of insecticides can be challenging.
In all cases, persons applying chemicals should follow label
Depending on the number of armyworms found, spraying a border around a
field rather than an entire field can be effective.
At this time the pyrethroid products used to control armyworms for hay
and corn are in short supply. Some chemicals have waiting periods.
Crops might not be able to be harvested in a timely manner and animals
might have to eat stored feed rather than pasture grass if
insecticides are applied.
Those who believe their property is affected can contact their local
Cornell Cooperative Extension for assistance.
— Heather Swanson