Q. I planted corn for the
first time this year, and had a real problem with corn
earworms. My family was totally
grossed out! Can you recommend a way to control them? I prefer not
to use chemical insecticides.
A. Corn earworms
cause the worst of their damage by feeding on the fresh silk and
boring into the tips of the ears of corn once the silk starts to
dry. Although I usually see them confined to the tip, they can feed
well into the middle of the ear, too. Damaged silk can interfere
with pollination, which results in partially filled ears of corn. In
addition to corn, corn earworms can damage tomatoes and peppers.
They are also known as tomato fruitworms and cotton
Life Cycle of Corn Earworms
Corn earworms overwinter in the southern United States and are blown
north on storms through the summer. Adults lay tiny yellow eggs
singly on corn silks and on the underside of the leaves. The larvae
vary in color from pink to yellowish-green to green to brown. They
range in size from about one-quarter inch to two inches long. Adults
are rather non-descript brownish-gray moths that you may not notice
since they are active at night. We have several generations annually
in our area.
The old measuring stick for corn growth:
"Knee high by the 4th of July"
Varieties of early and late corn
Early and mid-season varieties of sweet corn are usually less
bothered by corn earworms, while they are worst on varieties that
silk in September. Early varieties include Seneca Horizon, Seneca
Daybreak, and Sundance, while mid-season varieties include Sugar
Buns, Bodacious, and King Arthur. Some references also list certain
varieties of sweet corn as more resistant to this pest because they
have tight husks that wrap completely around the tip, making it more
difficult for corn earworms to get into. These include Country
Gentleman, Silver Cross Bantam, Calumet, and Silvergent.
Non-chemical earworm controls
One of the best non-chemical controls is Bacillus thuringiensis
(Bt), a bacterial stomach toxin specific to the larvae of
moths and butterflies. It must be ingested by the target insect to
be effective, but does not harm moths and butterflies that are not
feeding on treated plants. Bt does not have systemic
activity, and must be reapplied after rain and at certain intervals,
according to label directions. It is sold under trade names such as
Dipel, Thuricide, and Green Step Caterpillar Control. Since it works
best on small caterpillars - under one-half inch - be sure to start
applying Bt when ten percent of the crop is starting to silk.
It will not be effective on large corn earworms that have worked
their way deeper into the ear of corn.
If the damage is confined to the tip of the ear, simply cut it off
before taking it in to your family. There is nothing wrong with the
undamaged portion of the ear. Make sure to dispatch the larvae you
remove rather than throwing them on the compost pile so they do not
mature and add to your problem.
Fourlined plant bugs