Corn Earworm Management In Field Corn
LEXINGTON, KY.
Corn earworm is a pest
of many agronomic
and horticultural
crops and because of this
is has many common
names soybean podworm,
tomato fruitworm, and cotton
bollworm. Many growers
and consumers are
familiar with this insect in sweet corn as it
attacks the kernels at the tip of the ear. It
does the same damage in field corn, with
damage restricted to kernels at the ear tip.
Damage by this insect has been sporadic
with early and mid season corn escaping
some or all of the damage and late planted
field corn sustaining substantial damage.
Traditionally, corn growers have not had
practical and cost effective tools to manage
this insect and have accepted their losses
in the past, both in terms of yield and reductions
in quality.
Corn earworm can negatively impact field
corn in several ways. By feeding on kernels
at the tip of the ear, it directly can reduce
grain yields. Early –planted corn escapes
this damage, but ears of late-planted corn
can have 20 or more damaged kernels.
While kernels at the tip of the ear are generally
less valuable, this feeding may reduce
harvested grain by 2 to 8 bushels. In addition
to reducing yield, earworm can also affect
grain quality. Heavily damaged kernels
are lost during harvest, but partially eaten
kernels may end up in the grain. Damage to
the ear and grain itself provides entry
points for fungi and may increase rots. In
fact, corn earworm damage is one of several
factors that can contribute to aflotoxin contamination
in corn.
Corn earworm is attracted to corn while
the corn is silking. Fresh ear silks produce
volatile chemicals that attack egg-laying female
moths. So while the silks are fresh,
egg laying can occur if moths are active. To
control for earworm with insecticides,
sprays need to be applied during the silking
period and coverage needed in the center
third of the plant. As silks continue to
emerge from the ear, insecticides may need
to be reapplied to ensure protection. For
corn growers this has been both impractical
and rarely economical to treat field corn for
earworms. While sweetcorn producers can
get ground equipment over the shorter sweet
corn that is planted on smaller acreages,
field corn usually requires aerial application
during silking.
While corn earworm can overwinter in
Kentucky soils, colder winters reduce winter
survival. Early in the spring, moth activity
is usually the result of earworm moths
emerging locally. These local moth flights
often occur during silk emergence with corn
planted prior to mid May but pose little economic
threat in most years. However as the
year progresses, much larger corn earworm
moth flights arriving from the south are
more likely. Wind currents generated in advance
of low-pressure systems moving
across the plains and Midwest can move
large populations of earworm and other
pests northward. Late planted corn, read
that as planted in mid May or later in Kentucky,
silks later in the summer and is more
likely to be attacked by these large moth
populations. It is not uncommon to see the
tip of each ear with 20 or more earwormdamaged
kernels with late-planted corn.
Some of the newer Bt technologies on the
market can provide higher levels of corn earworm
control than earlier Bt technologies.
SmartStax, Optimum Intrasect, YieldGard
Vt2 Pro, and Agrisure Viptera hybrids have
improved control of secondary insect pests
of corn, including corn earworm. This can
be a valuable tool for Kentucky corn growers
particularly when they find themselves
in late-planting or replanting situations. Δ
DR. RIC BESSIN: Extension Entomologist,
University of Kentucky