David Owens, Extension Entomologist, owensd@udel.edu
Asparagus
Continue scouting for asparagus beetles and eggs. Thresholds from Michigan State University suggest a lower threshold than previously reported; 5% of spears with adults and 2% of spears with eggs. Labeled materials include carbaryl, (pay attention to rates pre-harvest) malathion, pyganic (OMRI) and permethrin.
Beans
First generation seedcorn maggot adults are very active right now. With the cool, wet weather this weekend and last week, any seed planted under tilled conditions (even if fairly minimal conservation tillage is used) should have an insecticidal seed treatment on it to reduce SCM damage.
Cucurbits
Continue scouting greenhouses and any transplanted melons or cantaloupes for aphid buildup. Aphids can severely impact seedling vigor when they build up in large numbers. If infested plants are not treated and aphids build up to the extent that leaves cup and curl and stunt the plant, it can be severe enough to reduce yield. Scout greenhouses now for aphids and spider mites on transplants. Aphids can be easily controlled with tray drenches of a neonicotinoid. A tray drench should also prevent cucumber beetle damage on transplant wagons, but tray drenches have limited residual activity once the transplants are planted and growing. Be sure to read the labels carefully to ensure that you have enough active ingredient left for a cucumber beetle application in the drip lines if needed after planting. For greenhouses with spider mite activity, the easiest time to treat the transplants is while they are on the transplant wagon.
Cucumber beetles typically start emerging in mid-May, although it is possible that they may do so earlier this year. Cantaloupe and summer squash are especially susceptible to bacterial wilt transmitted by cucumber beetle aggregations. Scout several areas in a field, sometimes aggregations are small but intense. If an insecticide application is to be made through the drip lines, pay special attention to label guidance on amount of product per 1000 feet of drip tape per given bed spacings. Following label guidance will help you avoid undertreating. We also produced a video on chemigation concerns last year which can be found here: https://www.youtube.com/watch?v=GaZlAFtBlNk.
Cole Crops
Diamond back moth is now active in addition to imported cabbageworm. Thresholds at this stage are fairly high at 20% infested seedlings of any caterpillar pest. If possible, avoid broad spectrum insecticides so as to conserve beneficial wasps as much as possible. Last year, we installed a cabbage plot where a parasitoid wiped out every single diamondback caterpillar early in the crop stage thus keeping even untreated plots clean at harvest. If using Bt, coverage is especially important. Bt can be quite effective on smaller plants when targeting smaller worms. Bt aizawai strains tend to be a bit more effective than kurstaki strains. Other cole crop pests active right now include flea beetles (seen primarily in brassica cover crop). If flea beetles and worms are present, diamides and spinosyns are effective on both among the more ‘narrow spectrum’ materials and Torac is also quite effective but a bit more broad-spectrum.
Sweet Corn
Scout sweet corn for cutworms. Consider a pyrethroid application if 3% of sweet corn plants are cut or if they exhibit 10% leaf feeding from small cutworms. See notes on cutworm activity in Field Corn in the Agronomic Crop Insect Report.