David Owens, Extension Entomologist, owensd@udel.edu
Sorghum
Keep a close watch for white sugarcane aphids. Low populations have been observed in several sorghum fields in Sussex and Kent, but in several fields, very isolated hot spots consisting of a couple of heavily infested plants can be found. Most sorghum is in the flowering stages, thresholds, depending on the source, range from 30% infested plants with localized areas of honeydew to 40-100 aphids per leaf. There are tolerant and resistant sorghum varieties listed on sorghum checkoff’s website: https://www.sorghumcheckoff.com/news-and-media/newsroom/2017/02/27/2017-sugarcane-aphid-tolerant-hybrids/; aphid count thresholds on these varieties are twice as high. There are only two effective insecticides for them: Sivanto and Transform. Sivanto has a 2ee recommendation for 4-6 fl oz/acre; 2019 insecticide trials showed that even 3 fl oz was effective. Transform’s rate is 0.75 to 1.5 oz.
Corn earworm is present in some fields, but for the most part at low levels. There is a very useful calculator for determining thresholds that can be found on Texas A&M’s website: https://extensionentomology.tamu.edu/sorghum-headworm-calculator/.
Soybean
Continue scouting for stink bug, corn earworm, bean leaf beetle, and defoliators. Soybean looper, the last member of the defoliator complex is now in the area at very low numbers. A few small earworm can be found in soybean. As a reminder, use the corn earworm threshold calculator for soybean at NCSU’s website: https://www.ces.ncsu.edu/wp-content/uploads/2017/08/CEW-calculator-v0.006.html
Pasture
There have been recent reports of true armyworm defoliating grass pasture, and fall armyworm may be present as well. Recent rains may help favor diseases that kill these caterpillars. True armyworm are less of a problem in pastures with broad leaf forages (see the guess the pest below). Armyworm eat far more leaf tissue during the last few days of their development than the early instars. You may notice birds working in hotspots. True armyworm is active at night, fall armyworm are active in the early morning and late in the day. University of Arkansas recommends a treatment if 3 or more mid-sized worms are present per square foot, paying special attention to the best portions of the field that are most attractive to moths. Arkansas also suggests using a gallon of soapy water (2 tbsp/gal) to bring caterpillars out into the open and out from the thatch.