| This caterpillar can measure
1/14 inches when mature and has a dark brown to grayish body with two pale yellow-orange bands
extending down the back. Adults are pale brown or brownish gray moths with a white dot in
the center of the front wing. As their name suggests, armyworms may "march en mass" to
another field when their food runs out. Corn or sorghum that is planted next to a small
grain field with heavy infestations of armyworms are subject to feeding injury as the hungry
caterpillars seek fresh food. Early signs of an infestation include leaves with ragged margins
that have been chewed. You may find "frass" i.e. the excrement from armyworm caterpillars,
around the base of wheat stems. Armyworm infestations tend to be focused around waterways,
areas of lush growth, or areas with lodged plants. These are the areas that should be
watched closely to determine if the whole field is infested, or the infestation is restricted to
a localized area.
Yield loss from armyworm feeding can occur in two ways. Armyworms feed on the flag leaf
and awns which causes physiological yield loss because the grain head won't completely fill.
Armyworms can cause direct yield loss by "clipping heads" as plants become mature and lose green
tissue. Fortunately, head clipping is rare in winter wheat. According to Kansas
State University extension entomologists, barley is much more likely to suffer from head
clipping.
Generally, if wheat is past the soft dough state, control is not warranted unless
obvious head clipping can be seen, and caterpillars are still present and feeding.
Worms feeding on the awns when plants are post soft dough will not cause enough yield loss to
justify the expense of an insecticide application.
To scout for armyworms, select several locations and search the ground and plant material for
armyworms in at least five random locations. Armyworms have a number of natural enemies
that help keep populations in check, if given a chance. In particular, parasitic wasps and
flies attack them. Parasitized armyworms can often be recognized by the presence of small
white eggs attached behind its "neck". The eggs are about the size of a period on a
newspaper. The suggested treatment threshold for armyworms is to treat if you find 4-5
unparasitized caterpillars per linear foot of row.
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The Oklahoma Cooperative Extension Service offers its programs to all eligible persons
regardless of race, color, national origin, gender, religion, age, status as a veteran, or
disability, and is an equal opportunity employer.
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