By Dave Grafstrom
In 2020, a widespread outbreak of true armyworm (Mythimna unipuncta), and the subsequent feeding, caused significant damage to perennial ryegrass seed fields in northwest Minnesota. Reported ryegrass seed yield losses ranged from 0 to over 80%. The most severe damage occurred over the July 4th weekend. The majority of the perennial ryegrass fields were sprayed once or twice for armyworms.