David Owens, Extension Entomologist, owensd@udel.edu
Soybean
The usual defoliator complex is active, including grasshoppers, cloverworms, leafrollers, Japanese beetle, and spider mites. Expect to start seeing Dectes emerge from the soil. Grasshoppers could be a threat to double crop fields given last year’s warm, dry weather and this year’s dry weather.
Reports have come in about spider mites building up on edges of fields. If caught early, it is possible to do a border spray of just a couple of passes. However, if mite populations build up in large numbers, they will often blow and ‘balloon’ into field interiors. We have a couple of true miticides that we can use: Zeal and Agri-mek SC. Agri-mek is the only labeled formulation for soybean. Both are translaminar, they move into the leaf and provide extended residual activity. Our other potential options are Lorsban, Dimethoate, and Bifenthrin (various trade names). These last three are most likely a 2-spray deal. If you use dimethoate, be sure that there is soil moisture and that the plants have not physiologically ‘shut down’. Dimethoate needs actively transpiring plants to move into the leaf tissue, otherwise it sits on the leaf surface and breaks down rapidly under UV light. Care also needs to be taken to ensure that your water chemistry does not degrade the product, particularly high pH or high iron. I have not tested bifenthrin enough to provide guidance with it at this time. I have seen field situations in which it worked well, but had it in a watermelon plot last year in which it did not provide much suppression. All three of these last products are largely contact materials and you need good coverage.
Corn
Now that small grains are being harvested, any stink bugs that have been developing on the grain are going to move elsewhere. Now is an excellent time to check edges of corn/wheat fields for stink bug and also for Japanese beetle. Stink bugs will often move to the edge of fields and stay there for a period of time before dispersing into the field interior. If an above threshold population is building up on the edge, a border spray may be all that is needed to protect the corn. Japanese beetle can do some whorl stage defoliation, particularly on edges of fields along pivot tracks. Pivot tracks act as an insect superhighway, so pay attention to them. I have not seen significant defoliation from Japanese beetle yet. Be sure to note their presence and scout the ears for silk clipping when the time comes.
Alfalfa
Continue scouting for potato leafhopper. Once yellowing is observed, damage has already been done. While scouting for leafhopper, note any blister beetles. If selling hay as horse feed, you may want to think about an insecticide before harvest to knock them down.