David Owens, Extension Entomologist, owensd@udel.edu
Alfalfa
Continue sampling for potato leafhopper. They can be easily found in soybean and snap bean and any alfalfa that does not have the glandular trichomes and is considered susceptible is at risk. Do not wait until you see hopperburn before deciding what to do about the hoppers. Also be sure to note blister beetles. Do not handle them if you see them in your net, the will break joints to expel a droplet of blood containing cantharidin which causes skin blisters. Horses are especially sensitive to canthardin and can become very sick from it. This year I have seen more blister beetle activity in weeds and other crops.
Field Corn
Japanese beetles are active and are a somewhat minor defoliator. Although eye-catchy, most beetle leaf feeding is minor and highly localized to specific parts of field edges. There are no defoliation thresholds. Some of the earliest corn is silking now, beetle thresholds are silks clipped back to less than ½ inch, less than half the plants have been pollinated, and beetles are present. Continue also looking for stink bug in corn. We are entering the growth stages that recently had threshold revisions.
Sorghum
Fall armyworm may start arriving in our area soon, and this worm can get into the whorls. Thresholds for whorl stage infestations is 75% of infested whorls. I mention this because grasshoppers have been showing up in some fields. The threshold for grasshopper is also fairly high. Available guidance from Georgia and Kansas fact sheets use 5-8 nymphs in field interiors as a threshold.
Soybean
Spider mites are present in numerous fields, especially around field edges that received some herbicide. The herbicide will drive mites out of the weeds, similar to mowing. Other insect pests that are common right now include Japanese beetle, thrips, green cloverworm, bean leafroller, grasshopper and blister beetles. Typically, pre-flowering defoliation thresholds are set at 30-40%, however, with the dry weather pattern we are in, it may be harder for the plants to compensate for feeding injury and thresholds are a tick lower. Bean leafroller seems to more common this year than in years past. Large numbers of grasshoppers can be found in some fields, particularly following a small grain cover or double cropped into wheat or barley. Pay close attention to defoliation in fields with grasshoppers in them. Stink bugs are also beginning to move into flowering fields. Stink bugs will not cause damage to beans prior to R3 – pod development.