Expect high levels of cutworm activity in northern Michigan this year

Moths have been laying yellow to orange-colored egg masses on structures across a wide area of the Upper Peninsula this spring.

Although the variegated cutworm is not usually thought of as a major pest in Michigan counties bordering Lake Superior, reports are coming in of an unusually high abundance of variegated cutworm egg masses being laid on structures all across the area. This insect has several generations per season, so homeowners seeing egg masses now can expect high levels of defoliation this year.

Insects and their activities are a normal part of our urban and rural ecosystems. On occasion, when the right set of circumstances comes together, insect populations explode. This spring, conditions appear to be favorable to a rapidly expanding variegated cutworm population

Cutworms are climbing caterpillars (moth larvae) that feed on a variety of plant foliage. They feed at night and hide in the daytime, usually in the soil debris adjacent to the plants they are feeding on. Alarmed home and cottage owners have been contacting local resource agencies with questions about the egg masses they are finding on windows and overhangs of their structures.

Female moths deposit these egg masses on houses and buildings as well as on grass, leaves and weeds in areas where the insect is active. The eggs are generally light yellow or orange when deposited and darken as they mature. The eggs are individually distinguishable in clusters of several hundred.

cutworm egg mass
Variegated cutworm egg mass.
Ken Gray Image courtesy of Oregon State University.

The fact that each egg is readily visible distinguishes cutworm eggs from the more familiar gypsy moth egg masses that we see on trees and buildings. Gypsy moth eggs are covered, giving the mass a fuzzy appearance, and individual eggs are not usually visible. Once trees have begun leafing out, gypsy moth eggs will have hatched, and only the tannish white residue will remain.

Gypsy moth egg mass
Gypsy moth egg mass.

Although variegated cutworms will feed on forest trees, garden crops and landscape plants should probably be of more concern to homeowners. In general, deciduous trees can withstand insect defoliation without too much negative impact on long-term health. Leaf feeding on yard shrubs and trees can be unsightly, however, and insect activity in gardens can be devastating in outbreak years.

Homeowners can destroy eggs by gently scraping them off into soapy water. Washing off buildings with a power washer or garden hose is an option but may not prevent egg hatch. Natural predators and disease agents in our environment should control outbreaks eventually, but in the meantime, damage may be considerable.

If caterpillar feeding on garden or ornamental plants becomes a problem, spraying vegetation with an approved insecticide is an option. Always carefully read the label of any insecticide and follow the instructions. Although effective, insecticides are poisonous and can harm pets, people and beneficial insects if not used with care.

For more information on general cutworm activities and some good non-chemical control suggestions, read Gretchen Voyle’s Michigan State University (MSU) Extension news article “Cutworms in the vegetable garden."

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