David Owens, Extension Entomologist, owensd@udel.edu
Soybean
Continue checking double crop fields for corn earworm. We were put onto a field two weeks ago with small larvae, treated them at 20 gpa Sept. 2 and the worms are currently medium sized. In our spray trial, pyrethroids were effective, but that is not always the case. Also, there were more soybean looper in the pyrethroid treated plots. Most of the loopers we are seeing are small. A good rule of thumb is 1 looper per sweep is a concern. Defoliation thresholds at R5 are 15%, at R6 between 20 and 30%, depending on where in R6. These defoliation thresholds are somewhat conservative.
Sorghum
Continue scouting for sugarcane aphid. If you feel that you need to treat because aphid populations are increasing, above threshold, and you are still in early/mid soft dough or earlier, the best options are Sivanto and Transform. Sivanto can be effective at sublabel rates of 2 to 3 ounces per acre. In last year’s aphid trial, Lorsban and Dimethoate knocked them back initially, but they quickly came roaring back.