Armyworms have been spotted in Addison, Franklin, and Grand Isle Counties of Vermont, as of July 9, 2015. Please don’t panic but do scout your corn and grass fields for armyworm caterpillars.
True Armyworm, Pseudaletia unipuncta, are typically spotted each year on some acreage in Vermont — crops most affected are grasses including field corn, grass hay and pasture crops. It is important for farmers and consultants to be monitoring fields–at high enough populations, armyworms can create a lot of damage very quickly.
To scout, look for caterpillars — when full grown, they can be almost 1.5 inches long. The caterpillars are usually greenish or brownish, but can be almost black. The sides and back of the caterpillar have light colored stripes running along the body. They normally feed at night and much damage can occur before they mature. Their preferred foods are grasses including corn, grains, and timothy but they will feed on other plants if grasses are unavailable. Feeding will start on the lower leaves and move upwards. A large population of armyworm caterpillars can strip an entire field in just a few days. When the field is eaten they “march’ to adjacent fields. Corn fields that are minimum or no-tilled into grass sod or fields infested with grass weeds are most susceptible.
For more information on armyworm, see “When Armyworms Come to Town” and/or True Armyworm resources on the Vermont Crops & Soils webpages. For additional scouting and control options, please contact Dr. Heather Darby at the University of Vermont Extension at (802) 524-6501.