What is fall armyworm and when does it hit?

Fall armyworm is a moth caterpillar that arrives in late summer (August-September) across much of the U.S., feeding heavily on grasses, hay fields, pastures, and late-planted forage. Severe infestations defoliate fields in days. Scout regularly in late summer; treat with Bt-based insecticide (Bt aizawai/kurstaki) or pyrethroids when caterpillars are small.