Fall armyworm was a significant pest for producers in Oklahoma last year, and this year is setting up to be the same scenario. It is out in full force already in some areas, and you may have seen or heard Dr. Tom Royer recently discuss how this insect has been active over this summer, especially on bermudagrass and fescue pastures. Wheat planting is already underway in some areas of the state. As wheat planting progresses here in September, producers need to check their wheat fields very regularly after seedling emergence. Fall armyworm can decimate large fields within a few days. Scout 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 will not get relief from fall armyworms until we get a killing frost. So make sure to keep scouting regularly, especially with this early-planted wheat!

Fall armyworm can cause significant damage like this 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.