David Owens, Extension Entomologist, owensd@udel.edu and Bill Cissel, Extension Agent – Integrated Pest Management; bcissel@udel.edu
Primary insect pests present in fields include green cloverworm, bean leaf beetles, aphids, stink bugs, and yellow striped armyworm. Aphid populations can increase quickly, so keep an eye out. Corn earworm trap captures have been low in some areas, high in others. Within the last few days, counts have come up quite a bit. Be on the lookout for earworm larvae in fields. Fields that are most attractive are later planted open canopy fields at R2. Worm development will coincide with the susceptible R4 to R6 stages. Worms at or before R2 do not typically require treatment. NC State has a very useful threshold calculator that takes into account row spacing, control cost, and price of beans: https://soybeans.ces.ncsu.edu/2015/08/managing-corn-earworm-in-soybeans/.
We have been conducting adult vial tests for monitoring corn earworm pyrethroid resistance, and have observed close to 30% survivorship. If you face a heavy infestation, 2-3 times above threshold, pyrethroids alone might not give enough control. We picked up our first small soybean loopers this week. This can be a significant defoliator. Base treatment decisions on defoliation estimates, and keep a close eye on fields that have loopers in them. Mississippi also uses defoliation and a ballpark figure of 10 loopers per 15 sweeps. Pyrethroid insecticides are generally ineffective on loopers. 2018 Spray trials from NCSU highlight high rates of Prevathon and Intrepid Edge as the most efficacious products. Other products that have resulted in good efficacy from other states include Steward and Radiant.