David Owens, Extension Entomologist, owensd@udel.edu
Soybeans
Continue scouting for bean leaf beetle, Dectes, defoliation, and stink bugs. Towards the end of this week coming or the following, be on the lookout for corn earworm. Our next moth flight will be starting soon. For Dectes, my only recommendation is to keep notes of which fields have the greatest number of Dectes and prioritize them in the harvest queue as early as the beans will allow – don’t let it sit for a long period of time, particularly if poor weather threatens during the harvest season. Defoliation thresholds during the reproductive stages decrease to around 20%. Well developed, full season bean canopies can withstand more defoliation, but double crop soybean cannot. Bean leaf beetle is active now, and may be damaging in isolated areas. Iowa State created a dynamic bean leaf beetle threshold that can be found here: https://crops.extension.iastate.edu/cropnews/2011/08/new-bean-leaf-beetle-threshold-calculator-created. Thresholds for July and August beetles typically come out to near 0.7 – 1 beetle per sweep, while second generation September beetle thresholds are nearly 4 times greater. Finally, be scouting for stink bugs in any fields in the R4 stage. Our threshold is 5 bugs per 15 sweeps.
Corn
Corn rootworm adults are now active. If you plan to follow 2nd year corn with 3rd year corn (or older continuous corn), and especially fields in New Castle County and western Kent county on heavier ground, look at the ears for rootworm. A good rule of thumb is 1 rootworm per plant warrants mitigation action for next season’s corn.