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Corn Earworm
Corn earworm is a serious insect problem in
Colorado, especially in the southern and western parts of the state. Corn earworm larvae feed on ear
tips and cause substantial injury.
The corn earworm does not over-winter in Colorado. The adult moths migrate each year
from southern areas and lay eggs on ear silks. Eggs hatch within a week. The larvae initially feed on silk and then move into the ear tip.
Corn earworm moths are most active during evening
hours. Adult moths are about
an inch long, robust and range from olive green to dark red in color. In Colorado, these moths appear in
summer and are attracted to fresh corn silk where egg laying occurs. Pheromone traps are available for
detecting corn earworm moths.
Occurrence of moths in traps is useful for timing of control.
Ear damage from corn earworm larvae is characterized by
extensive excrement at the tip of the ear. The young larvae clip off silks
and then proceed into the ear where they remain until ready to pupate in
the soil. There are five to
six instars (larval stages) and the appearance and color of the larvae
change with each instar stage.
Control of corn earworm involves biological, cultural,
and chemical methods. Natural
predators include small wasps, lacewings, minute pirate bugs and damsel
bugs. These natural predators
feed on corn earworm larvae.
Early sweet corn varieties will have fewer corn earworm problems
than later developing varieties.
Biological insecticides for corn earworm include Bacillus
thuringiensis, a bacteria sold under a variety of trade names, and
Spinosad, another microbial insecticide. Cabaryl and permethrin are
synthetic insecticides that can also be used for corn earworm
control. Insecticidal
treatments should be applied during the silk stage.
For more information, see the following Colorado State
Extension fact sheet(s).
For more information, see the following Planttalk
Colorado™
script(s).
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