Jeffrey Hahn, Asst. Extension Entomologist
A large flight of variegated cutworm moths moved through Minnesota as well as Wisconsin this spring. This was particularly noticeable when clusters of eggs were found on many buildings and other structures during May (see June 1, 2012 Yard and Garden News)
The result of this activity is now being felt in home gardens as many different herbaceous plants that are being damaged by their feeding. Unlike subterranean cutworms that many gardeners are familiar with, variegated cutworms are a type of climbing cutworm that will feed on the foliage of plants. They typically chew irregular holes between the veins on the leaves. They have also been known to bore into flower buds. Be careful not to confuse variegated cutworm feeding with slug damage which can look similar. Slug feeding usually results in more ragged, irregular holes but to be sure, you may have to catch the culprits in the act.
Variegated caterpillars are generally dark-colored, ranging from brownish to black. There are four to five yellowish diamond-shaped spots on the top of the body starting at the head. They may also have a dark-colored 'W' on top of its body near the posterior. Like other cutworms, variegated cutworms curl into a ball when they are disturbed. These cutworms are large when mature, growing to 1½ to two inches long.
The biology of variegated cutworms in Minnesota is not clearly understood. They apparently can overwinter in Minnesota either as pupae or larvae. However, most of them are probably carried up on the jet stream as adult moths and deposited into Minnesota during spring. They are reported to have two generations in the northern U.S. so we can expect to see them throughout the summer.
If you are experiencing problems with variegated cutworms, you have several options for managing them. You can try handpicking them. You might even be able to put out boards and trap some. If the problem is severe enough, you may resort to insecticides. Spinosad is a good option if you are looking for a low impact product. There are also a variety of residual insecticides to choose from, including permethrin, bifenthrin, cyfluthrin, and carbaryl.
A question that gardeners in northern Minnesota are asking is whether they will now start seeing this insect every year when they rarely or never saw it before. The good news is that the odds are in northern Minnesota's favor for not witnessing a repeat performance by variegated cutworms next year. We would have to experience the same perfect storm of weather conditions that allowed such a large number to migrate up to northern Minnesota and that is not likely.