What Are These Caterpillars Doing To My Corn?
MT. VERNON, ILL.
Spring is here again and
with its arrival farmers
are hard at work planting
their crops in the Midwest.
This year, weather conditions
have been favorable and, as
such, many farmers have already
planted their corn and
are making plans to put soybeans
in the ground shortly. While farmers are
working, their insect foes are hard at work as
well. One of those foes is the black cutworm.
Black cutworm, Agrotis ipsilon, is a common
pest of corn that does not generally
overwinter in Midwestern
states. Rather these members of
the Noctuidae family fly and are
carried northward by springtime
storm fronts from southern and
southwestern states where they
can survive the winter months.
In Illinois, more than 75 percent
of the corn crop has already been
planted as of May 1. Seedling corn
is highly susceptible to damage by
black cutworms, so farmers are
encouraged to scout fields for potential
black cutworm injury.
Black cutworm moths will lay
their eggs on crop residue, and
since they prefer soybean residue
over corn, first-year corn is generally
at greater risk to black cutworm
injury than continuous
corn.
Another highly effective tool for
black cutworm management is
knowledge of when these moths
first arrived in your area. Traps
baited with an attractant
pheromone have detected an intense
flight of these moths in
much of Illinois from April 23 to
April 26. Using the date of this
first intense capture as the biofix
date, one can calculate how long it
will take the progeny of these arriving moths to
develop enough to cause damage in your corn
field. This is done by calculating the number of
degree-days that have elapsed since their arrival.
Degree-days are an effective tool to help determine
when to start scouting for black cutworm
larvae. Degree-day accumulation begins
with an intense capture of moths (nine or more
cumulative moths caught in pheromone traps
over two consecutive days).
Black cutworm larvae normally begin cutting
corn when approximately 300 degree-days,
(base 50 degrees F), are accumulated after an
intense capture occurs. Cutting dates for Illinois
farmers can be predicted by using the Degree-
Day Calculator at the University of Illinois
IPM (www.ipm.uiuc.edu/degreedays/) and
WARM (www.sws.uiuc.edu/ warm/pestdata)
websites. Farmers in other states as well as Illinois
can use models supplied by their state Extension
service or the USPEST calculator at
http://uspest.org/wea/.
Early signs of cutworm feeding are pinholes
in the leaves of newly emerged seedlings. This
symptom can occur before 300 degree-days
have accumulated.
Areas of fields in which early-season weeds
(winter annuals and perennials) were growing
at the time moths flew in are at a higher risk
than weed-free fields. If tillage or herbicides
eliminate weeds one to two weeks before planting,
black cutworms that had been present
probably starve to death. The presence of weeds
only a few days before planting increases the
likelihood of cutworm damage if larvae are
present in the field.
Even though corn may have been treated with
a neo-nicotinoid seed treatment such as Poncho
®, field scouting is still warranted. Cut,
missing or wilted corn plants are typical symptoms
of black cutworm larvae damage. Feeding
mainly at night, larvae will move up the row as
they feed. On average, one larva may cut three
to five plants in its lifetime.
Treatment thresholds are when 3 to 5 percent
or more of the plants are cut and larvae are
present. One should also consider the location
of the cutting (above or below the growing
point), size of the cutworm, and the soil conditions
(moist or dry).
For further information on this pest, including
scouting and management strategies, contact
your local Extension office. Δ
DR. DOUGLAS B. JONES: Extension Specialist,
Integrated Pest Management, University of Illinois
Black cutworm larva and cut corn seedling.
Photo courtesy of University of Illinois