Armyworms tend to favor the grassy margins of fields, and often pre-emptive treatments of these borders can prevent field injuries. Scouting is best done at dawn and dusk, when armyworm and fall armyworm are active feeding. Sampling should be carried out throughout the season. Armyworm populations seldom reach economic levels or require treatment. Cultural methods can also affect armyworm populations.
Weedy fields are most at risk, as well as no-till fields planted with small grains or cover crops.
References O'Day M, Becker A, Keaster A, Kabrick L, Steffey K. 1998. A Diagnostic Guide. Missouri University Extension Publication 166. Entomology and Pest Management. Macmillan Publishing Company.