In previous years, portions of eastern Nebraska have seen unprecedented numbers of fall armyworm caterpillars feeding on alfalfa, brome regrowth in pastures, and newly seeded small grain crops such as wheat, triticale, and rye. While reports of armyworm damage have not been received so far this year, it is a good idea to keep an eye out for this insect.
Fall armyworm caterpillars can be distinguished from other Lepidopterans by markings on the head that resemble an inverted “Y” and four spots on the last abdominal segment that form a square. This insect does not overwinter in Nebraska, but rather migrates north from southern states when populations build up in late summer. Once caterpillars are ¾ inch, they can do considerable damage in a few days. Because of this, it is important to scout fields and pastures in the early morning and late afternoon, when caterpillars are most active, to spot them when they are small.
A reasonable treatment threshold is finding 3 or more caterpillars per square foot within a field or pasture. There are several insecticides labeled to control this insect including Mustang Maxx, Besiege, and Sevin. For forage crops be sure to check the grazing restriction and post-harvest interval. When considering a chemical treatment option, keep in mind caterpillars ¾ inch or longer are close to maturity and can be harder to control with an insecticide.
Fall armyworm feeding declines with cooler temperatures and the adult moths eventually migrate south. In the meantime, be sure to keep an eye on your pastures and newly seeded fields for any sign of infestation.