David Owens, Extension Entomologist, owensd@udel.edu
Corn
Western corn rootworm adults are active and worth scouting for if planting corn in the same field as this year’s, and especially in western Kent or New Castle County where the ground is heavier. Threshold for next year management (Bt variety with rootworm traits or soil insecticide application) is 1 beetle per plant. I was asked recently what I thought of insecticides tank mixed with a fungicide application. The threshold for stink bugs is 10 bugs per 100 plants for tassel push or tasseling plants but go up to 28 bugs per 100 plants during the early silk stages. Most stink bugs in corn tend to be brown stink bugs which are difficult to kill with pyrethroids. Of them, bifenthrin does the best job, but is also a bit more expensive. In the absence of scouting, a prophylactic tank mix may be of some benefit around edges only, but I don’t see it as paying for itself in field interiors. Of course, this is difficult to manage if a field is being treated by plane.
Soybean
Now that full season bean fields are entering early pod stages, begin paying special attention to stink bugs, podworm, and defoliation. Generally, podworm are not an issue in full season bean fields but come the 3rd week of August can be a major threat to double crop bean fields. I will post the NCSU earworm threshold calculator now through August for soybean as a general reminder about this handy tool: https://www.ces.ncsu.edu/wp-content/uploads/2017/08/CEW-calculator-v0.006.html.
Stink bug thresholds are 5 bugs per 15 sweeps. There is some thought in Mid-Western states that this might be a bit high in R4 soybean. I think a lower threshold is justified in Plenish soybean on account of their higher value and need for higher quality. Soybean grown for seed the thresholds are 2 – 2.5 stink bugs per 15 sweeps. Pay attention to which species are in a field. Brown stink bugs should be treated with bifenthrin or an organophosphate such as Orthene, while green stink bugs are susceptible to all of the pyrethroids.