Vegetable Crop Insect Scouting

David Owens, Extension Entomologist,

Begin scouting greenhouses for aphids and spider mites on early season transplants. Aphids can easily establish on transplants and build up moderate sized colonies in hotspots. These hotspots can be identified by increased ant activity on the plants or by curling leaves. Should transplants be found with aphids, a tray drench treatment of a neonicotinoid will remove the aphids and provide some degree of short-term cucumber beetle protection. Heavily impacted plants may be so stunted that they might never yield.

Signs of spider mite feeding include yellow striping on the upper surface of the leaf indicating mite feeding on the leaf underside. It is easier to treat trays than to clean up a field after infested plants have been transplanted. Focus mite scouting in areas near sidewalls or where weeds may be present inside the greenhouse.

Cole Crops
With warm weather, many of our cole crop pests have broken dormancy and are searching for food, including imported cabbageworm, diamondback moth, and harlequin bug. This past winter was cooler than 2022-2023 but wasn’t ‘cold’ and not nearly cold enough to set any of these pests back.

Warm weather earlier in the week may have been enough to allow colorado potato beetles to emerge and start looking for early emerging potato. Once temperatures are in the upper 70’s to low 80s adults will begin flying. Cool weather in the week or so ahead should slow them down if they have not yet been spotted on new plantings.

It might seem odd to mention spider mites given all the rain and cool weather we have had, but strawberries are an excellent early season host for mites. Mites overwinter quite comfortably under row covers and begin reproducing in earnest once the plants enter flowering and fruit set stages. Plants on black plastic also warm faster, stimulating mite activity. Thresholds for plants beginning to flower are 15-20 mites per leaflet or 50% of sampled leaflets with mites on them.

Scout for asparagus beetle activity on emerging spears. Asparagus beetle lay dark cylindrical eggs on spears perpendicular to the spear. Thresholds from Michigan State University suggest a threshold of 5% of spears with adults and 2% of spears with eggs.