David Owens, Extension Entomologist, owensd@udel.edu
Field Corn
Continue scouting corn field edges for stink bug activity. Concentrate your search on the leaf above the primary ear to 2 leaves below the primary ear. Often times, stink bugs will move sideways onto the opposite side of the stem or they will be hiding between the stem and the developing ear or flag leaves. The threshold for tasseling corn is 10 bugs per 100 plants. This increases to 28 or more bugs at R1 and R2. Pay attention to signs of excessive silk clipping from Japanese beetles, particularly along field edges (especially if smartweed has been defoliated and corn has not begun silking) and along pivot tracks. It is unusual for there to be enough silk clipping prior to pollination to justify a treatment.
Soybean
The usual defoliator complex is present, but so far seems to be rather quiet. Dectes stem borer is beginning to emerge out of the soil. It will take adults several days to feed before they begin mating and laying eggs. In previous years, stem borer activity peaks between mid to late July. They are highly attracted to sunflowers, which, if planted near a field, can serve as a trap crop and a large number of beetles destroyed with a well-timed insecticide application to the sunflower. Whether or not this prevents damage is unknown. UD and UMD entomologists wrote a very comprehensive fact sheet on Dectes stem borer which can be found here: https://www.udel.edu/academics/colleges/canr/cooperative-extension/fact-sheets/dectes-stem-borer/. Please note, I do not recommend treating a soybean field with foliar insecticides for Dectes management. Joanne Whalen did several large-scale trials with wildly inconsistent results, all of which is discussed in that fact sheet.
Sunflower
This week, Asiatic garden beetles were observed to cause significant sunflower defoliation prior to flowering, such that the edge most rows of a block experienced greater than 75% defoliation. Check for signs of excessive defoliation. Asiatic garden beetles hide in the soil during the day, you may see holes in the ground where the adults burrowed.