Black Cutworm Infestation Likely In Missouri
COLUMBIA, MO.
Farmers with late-planted corn should prepare
for black cutworm damage. Wet soils
and heavier weed cover in fields will make
the insect a potential problem this year, said a
University of Missouri Extension entomologist.
“This is a perfect year for black cutworm,” said
Wayne Bailey. “The whole northern part of Missouri
is at risk, but we’ve had the heaviest moth
captures in the northeast. This means there is a
high risk of
black cutworm
in that area,”
Bailey said.
Winter annual
weeds like henbit
and chickweed
add to the
risk. “Black cutworm
moths
tend to lay their
eggs in fields
with vegetation,
because their
larvae can feed
on that prior to
feeding on
corn,” he said.
“But these
plants will be
older and
tougher when
corn emerges,
and so they will
go for the corn.”
Late-planted
corn is a perfect
target for the insect.
Wet fields delay planting, but attract cutworm
moths to lay eggs. When corn plants
emerge, there will be more and bigger cutworm
larvae to attack seedlings. When corn is planted
on time, emerging plants have a head start on
growth before larvae reach the cutting stage.
“They can cut above or below ground. If they
cut above ground, the corn may come back in
one to two weeks, depending on field conditions,”
he said. “If they cut underground, that’s
closer to the growing point. The plant could die,
but if it lives, the yield potential is reduced.”
Black cutworms are considered the most damaging
corn cutworm species. Moths overwinter
in southern states and migrate north on winds
in storm fronts from mid-March to June.
While cutworms rarely damage an entire corn
crop, farmers can lose up to 50 percent of their
plants in heavy infestations if cutworms go undetected,
Bailey said. Farmers will know if a
stalk was cut by a worm if the cut line is horizontal.
Diagonal cut lines are likely caused by
voles, he said. Wilting plants are one sign of
worm cutting.
Bailey said farmers should start scouting fields
for signs of foliar damage or cutting five to seven
days before the predicted first cutting date for
their area, and continue scouting until corn
reaches the five-leaf stage. Cutting dates are
based on when the first intensive moth captures
took place.
For northern Missouri, the predicted first cutting
is May 17. Other dates are May 11 for western
Missouri near Nevada and May 13 for eastern
Missouri near Union and St. Louis.
“In the northeast, I’d definitely be out there
scouting,” Bailey said. “The larvae are small and
nocturnal, so they may be hard to see. But you
may be able to see defoliation on plants. If you
don’t see feeding, it doesn’t mean you shouldn’t
look again at the predicted cutting date.”
Farmers have three options to handle cutworms.
First, plant seed corn treated with insecticide.
“But those worms will be large, and if
their numbers are heavy, it will take a high dose
to knock their numbers down,” he said. “So seed
treatments will be less effective this year.”
A second option is to use an early-season
spray to knock down heavy populations. “We
don’t usually recommend this method, because
we like to know the pest is present first. But if
populations will be heavy, it is viable,” he said.
Bailey said the preferred strategy is to scout
fields and apply insecticide where needed to rescue
plants from the worms.
“If the cutworms are below ground and they’re
cutting 2 to 4 percent of your plants, I would put
a foliar rescue on top,” he said. “Once you’ve
sprayed, check back in about three days to
make sure there are no more cuttings.”
Once corn plants reach the six-leaf stage, they
are less vulnerable as their stems are usually
too thick for worms to cut.
“We will worry about corn until it is about 6 to
7 inches tall,” Bailey said. “Usually the worms
are down feeding near the ground. On wet soils,
they tend to surface feed, whereas on dry soils
they tend to feed underground – so we have that
going for us.”
For more information on black cutworms or
the MU Extension black cutworm monitoring
program, visit
http://agebb.missouri.edu/weather/reports/bcwforecast.htm. Δ
Adults are gray, nocturnal moths with a small black dagger-like marking on each
forewing.
Photo by David Pinkerton