David Owens, Extension Entomologist; owensd@udel.edu
Soybean
Full season bean fields are at R6-R7. At R6, defoliation thresholds rise, as do stink bug thresholds. Soybean aphids no longer become a threat to yield at R6. At R7, thresholds rise even more for stink bug, and I reckon you would be able to smell the field from the roadside if a high enough population were present at R7 to justify a treatment. Double crop soybeans should continue to be scouted for defoliators, especially soybean looper. Earlier this season we installed a spray trial for corn earworm in a field that also had about 0.75 loopers per sweep. North Carolina’s Dominic Reisig gets interested and concerned once populations rise to greater than 1 per sweep. Besiege at its high rate knocked them back and they have not recovered to the same pre-treatment level. Lannate came close to zeroing them out at 4 days after application, but at 11 days after application, the numbers were equal to the untreated check plot and greater than before treatment. These represent small loopers just hatched. It may be that so-so control is a better way to go, delay loopers long enough for beans to pass into R6. Better looper materials (although probably much more expensive and harder to find) include Denim, Steward, Intrepid Edge, and Radiant. Continue scouting for stink bugs as well in double crop beans. The late planted soybeans tend to see an increase in stinkbug pressure. Bean leaf beetle populations appear to be low this year. Grasshoppers can also damage small pods in addition to defoliating leaves. Finally, this is the first week in 5 that no reports of soybean aphid populations came in but keep scouting those double crop beans. Threshold is 250 aphids per plant at or prior to R5, with an increasing population 3-4 days later. In our fields in Georgetown and Harbeson, natural enemies are working on them.
Sorghum
Continue scouting late sorghum for sorghum aphid. Thresholds are 30% infested plants (with a quarter sized colony on a mid-canopy leaf) and honeydew present up through soft dough. Available materials include Transform, Sivanto, and Sefina.