Watch Out For Large Underwing Moth Larva

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Last fall, we described a new turfgrass pest that was causing some damage in the Seattle area. At the time the article was written, the insect was thought to be an army cutworm. Since that time, we have learned that it is the larva of the Large Underwing Moth.

Underwing Moth larva1

This insect was accidentally introduced from Western Europe and was first founded in 1979 in Nova Scotia, Canada.  According to a bulletin from the University of Idaho’s Extension service, the first moths were collected flying around a porch light in Nova Scotia. There is no information on how it arrived in North America. The bulletin also stated that once the insect was established, it moved south and west and is a potential threat to winter wheat and barley. What makes it challenging is that it feeds during the winter months, which is the same time as the feeding period of another major turfgrass pest in the Pacific Northwest, the European Crane Fly larva. Although it is not known to be a major turf grass pest, it will feed on bluegrass from fall through early spring. As you can see from this picture, which was taken in March, the damage can be extensive.

Moth damage

As with other cutworm species, these larva feed during the evening hours and hide during the day. The Black Cutworm, a major insect pest on golf courses, will dig into the soil on greens and tees during the day. When disturbed, cutworms will curl up into a c-shape. Once they are done feeding, the larvae will burrow into the soil to make a cocoon. They will pupate in May and the adults will emerge and be more active at night. The females will then lay eggs (a single female can lay up to 2,000 eggs) through August, but they can be active all the way until October. Fortunately, cutworms just feed on the upper part of the grass plant and it usually recovers from such damage. As long as the crown of the plant has not been damaged, the turf will regrow new grass blades.  This can be helped along by fertilizing the lawn.  In severe cases, some reseeding may be necessary. If you think your lawn may have an insect problem, contact your local Spring-Green office and have them come out to inspect your lawn. It is the best way to keep your lawn looking green.