With wheat planting beginning in some areas of the state during the last week of August into the first week of September, we have already received several calls regarding fall armyworm feeding. Dr. Tom Royer, Extension entomologist, said fall armyworms have been very active this summer, showing up early and in large numbers this growing season.

As wheat planting progresses here in September, producers need to check fields very regularly after seedling emergence. One producer had significant damage occur across an entire 1/2 section within 2 days. Dr. Royer suggests scouting for fall armyworms by examining plants in several (5 or more) locations in the field. A good place to start is along the field margin as they sometimes move in from the road ditches and weedy areas, but make sure to examine the interior of the field as well. Fall armyworms are most active in the morning or late afternoon.

Fall armyworms are small (3/8-1 1/2″) and can be easily overlooked (top photo). Feeding on leaves gives a transparent (“window paned”) appearance (bottom photo). Photos courtesy of Dr. Tom Royer.

Be on the lookout for “window paned” leaves, and count all sizes of larvae. The suggested treatment threshold is 2-3 larvae per linear foot of row in wheat with active feeding. Numerous insecticides are registered for control, but they are much more susceptible when caterpillars are small. We won’t get relief from fall armyworms until we get a killing frost. So make sure to keep scouting regularly, especially with early-planted wheat!

Fall armyworm can cause significant damage across large areas very quickly, so scout early and scout often. Photo courtesy of B. Boeckman.

Control suggestions for fall armyworm are available in the OSU Fact Sheets CR-7194 Management of Insect and Mite Pests of Small Grains.