True Armyworm Alert: pest outbreaks in Southeastern Minnesota

By Ryan Miller – Crops Extension Educator, University of Minnesota Extension and Bruce Potter – Potter Brother’s LLC and University of Minnesota Extension IPM specialist, retired

 

Varying sizes of true armyworms

Now is the time to scout for true armyworm throughout MN, outbreaks may not be limited to Southeastern Minnesota.  Fields of highest importance are row crop fields with later terminated cereal rye cover crops and grass hay fields.  Time is of the essence as true armyworms are voracious feeders and move quickly from field to field in search of viable food sources.  They can decimate a corn crop almost overnight. 

True armyworms remain hidden during daylight hours and can be more difficult to find.  Search under clumps of terminated cover crop and under soil clods.  Sweep nets can be useful when scouting grass hay and grass waterways. 

The University of Minnesota Cooperative Black Cutworm Trapping Network Report #5, indicated that on April 24^th a trap in Houston County, MN had a capture of 22 moths and was continuing to capture moths.  Unfortunately, this is only an indication that large numbers of moths have arrived, it does not locate where they will become a pest problem.  It’s imperative that farmers in the southeast region scout their field for problems, they will not be an isolated problem for Houston County.  This morning true armyworms and crop damage were reported in Olmsted County Minnesota.

Photos from June 10^th, 2026 in Olmsted County Minnesota.

Armyworm feeding damage on corn with late terminated cereal rye cover crop

Armyworm feeding damage on grass hay field

True Armyworm Management

Only Bt corn hybrids containing the Vip3a protein are labeled for true armyworm control and more information can be found on this link.  Here is a good link for information on managing true armyworm with foliar insecticide.