Armyworm alert in northern Michigan and Upper Peninsula

There is a widespread outbreak of armyworms across Michigan’s northern Lower Peninsula and Upper Peninsula.

(A) Armyworm damage on leaf edges, which appear ragged due to feeding. (B) Closer inspection of the plant will reveal armyworm larvae hiding in the leaf whorl. (C) Armyworm caterpillars have vertical stripes running down their back and sides, as well as a head capsule with a mottled yellow appearance. The key feature for identification are the black bars above each of the back legs. Photos by Fred Springborn, MSU Extension.

Armyworms have been found in high numbers in crop fields in several Michigan counties including Charlevoix, Manistee, Isabella and many parts of the Upper Peninsula. Check corn, oat, rye and wheat fields and grass pastures for potential feeding damage. Also, check other crop fields that have these listed crops growing next to them as the worms will march out of a preferred crop field and hit the next closest crop when they start to run out of food.

If the caterpillars are approaching 1.5 inches in length, which the ones in Manistee County were on July 13, 2018, insecticidal applications are not recommended as the feeding is just about complete. Not all corn with insecticidal genetic enhanced traits are labelled as effective for armyworms. Check out those details in “The Handy Bt Trait Table for U.S. Corn Production.”

Contact your regional MSU Extension field crops educator for more details.

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