Variegated Cutworm Update

Variegated Cutworm Update

Bryan Jensen (IPM Program), Eileen Cullen (Dept. of Entomology)

The calls and emails continue to come regarding variegated cutworm damage.  This has been, to say the least, an unexpected and unprecedented infestation and certainly warrants scouting.  Variegated cutworms are routinely observed in several crops and ornamentals but not to the level of damage seen this growing season.  Reports of damage have been from all areas of the state, on several crops and the larvae are variable in size.  Careful scouting over the next few weeks and perhaps the rest of the growing season will be important.

Reports on alfalfa have come from both new seedings and established stands.  Harvest would be your first control option if second crop is ready.  If harvest is not an option, an applicable economic threshold would be 2 larvae/square foot.  Larvae may be difficult to find during the day.  Check under leaf/stem litter and look in soil cracks.  We’ve even had consultants indicate they will crawl in worm holes and a shovel was useful for detection.  Once the alfalfa is harvested, windrows provide excellent cover and may increase survival if the weather is hot and dry.  Be sure to check all these areas to confirm their presence before spraying.  Lack of regrowth could also be from dry weather the southern part of the state has been experiencing.

Several damage reports have also come from soybeans and range from light defoliation to almost complete consumption of seedling plants that includes loss of all growing points.  Some injury has resulted from larvae migrating out of adjacent crops and other infestations have been spotty within a field. In those situations, spot spraying may be an option.  Consider treating entire fields if you have an average of 40% defoliation prior to flowering.

Reports have also come from field and sweet corn, however, those reports are limited and not as severe.  Late planted field and sweet corn are certainly fields to watch closely for defoliation and perhaps stand loss.

Variegated cutworm larvae will range in size from 1 ½ to almost 2 inches in length prior to pupating and can be a good indication that feeding will soon subside. However, we’ve had reports and samples of larvae that are approximately one half grown and/or populations that have mixed sizes.  Best efficacy will come when larvae are small.  Continue to check for variegated cutworm larvae and damage.

We are likely to see future generations as the summer progresses.  However, it is unpredictable if these generations will cause similar problems as what we are seeing now.  Often predators, parasitoids and diseases may help control populations.

For more information on please see last week’s article on variegated cutworms.