David Owens, Extension Entomologist, owensd@udel.edu
Alfalfa
Continue scouting for potato leafhopper on alfalfa less than 12 inches tall. Cutting alfalfa destroys nymphs and forces adults out of the field, but if there is a sequence of cuts, it may push adults onto older cuts that are growing but less than 12 inches.
Soybean
There are numerous defoliators present. With dry weather, canopies on barley and wheat beans are slow to close and thus the impact of defoliators is greater. Spider mites are still a concern, even with recent rains. If mites are present on half of the plants sampled, those plants are showing stippling or defoliation on a third of their leaves, and mites exceed 20 per leaflet, consider a miticide treatment (abamectin or etoxazole). Beans not under drought stress can tolerate more mites than those that are. Rain and high humidity favors pathogens that can destroy mites. Infected mites will be brown and have a slightly fuzzy appearance. While scouting, take note of fields with higher Dectes counts, particularly full season bean fields, to prioritize them for as timely a harvest as possible. Scout for stink bugs in full season bean fields that are beginning to set pods. The stink bug threshold is 5 bugs per 15 sweeps; less for Plenish soybean, and 2.5 bugs per 15 sweeps for seed soybean.
Sorghum
Begin scouting for sorghum aphids. They tend to first appear on mid-canopy leaves or lower. There are a couple of species that may be present; sorghum aphid (formerly white sugarcane aphid) has small cornicles that are the same color as the aphid. They have a light, white-yellow appearance, whereas the seldom important yellow sugarcane aphid is considerably larger and has a dark lemon color. Corn leaf aphids may be present in sorghum that is in boot stage. Typically, I don’t worry about this aphid too much in sorghum, but this year they might cause enough stress to drought stressed plants to cause concern. Corn leaf aphids concentrate around the flag leaf, are smaller, rectangular, and green; populations usually decline rapidly once the head emerges. Sorghum aphid on the other hand reproduces extremely fast in high temperatures.