David Owens, Extension Entomologist, owensd@udel.edu
Soybean
Continue scouting full season bean fields for stink bugs and defoliation. Remember, defoliation thresholds do decrease during the reproductive stages. Most of the full season bean fields I have seen have a well-developed canopy and although defoliation thresholds do decrease, these plants could probably take a real beating before losing yield potential. Defoliators active include green cloverworm, Japanese beetle, and grasshoppers. In 2020, we did a grasshopper efficacy trial. If you are targeting grasshoppers in either soybean, hay, or other crops with a pyrethroid, use the highest label rate. Dimethoate worked very well in our trial, and Prevathon (now Vantacor) tank mixed with MSO, was superb.
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. Soybeans 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 the pyrethroids.
Alfalfa and Hay
Continue scouting cut alfalfa for potato leafhopper. Cutting will destroy most of the nymphs, and adults will leave a cut field temporarily. The problem is when they come back and build up on smaller plants allowing them the opportunity to affect yield.
In grass pasture, take a moment to scout for grasshopper and armyworm damage. Both fall and true armyworm are active right now. Pay special attention to the thatch layer to make sure large populations of worms are not building up.