David Owens, Extension Entomologist; owensd@udel.edu
Soybeans
Soybean aphids continue to be active in the area, although populations appear to be declining in general. The threshold the Midwest uses for them is 250 aphids per plant prior to R5, and to resample the field 5-7 days later to see if the population is still expanding. Once we reach R5, it is generally thought that infested plants will not yield differently from non-infested plants.
Corn earworm continues to be very active in double crop soybean right now. Continue scouting for them and use NCSU’s corn earworm calculator site: Corn Earworm – Soybean Advisor. In most cases, a low rate of Besiege should provide good control of CEW while also controlling aphids.
Soybean looper is a bit of a wild card right now. It is moving through the area. Night time temperatures in the 50’s help slow them down a lot. It’s a tropical species that does not appreciate cool weather. There are also quite a few parasitoids that get into soybean looper. Soybean looper is only partially controlled with diamide insecticides. Lanate, Denim, and Intrepid Edge are all good options. NCSU has a good fact sheet on estimating looper defoliation potential here: Soybean Looper Defoliation Guide | NC State Extension.
Finally, if experiencing significant defoliation, particularly in double crop beans, make sure that there are still worms to hit. Sometimes, worm populations disappear before they exceed threshold. Remember, defoliation thresholds are conservative, especially if good soil moisture is present.
Sorghum
Pollinating or just recently pollinated sorghum should be scouted next week for podworm. Shake 30-50 heads against the side of a bucket to dislodge worms. As a general rule of thumb, one earworm or armyworm per head can result in a 5% yield loss. Texas A&M has a great threshold calculator here: https://extensionentomology.tamu.edu/sorghu m-headworm-calculator/ Sorghum aphid or white sugarcane aphid is unusually active this year. Later planted sorghum (see above) is at risk. Scout by looking at the undersides of mid-canopy leaves and taking notes of areas with honeydew present. Threshold is 30% infested plants with localized areas of honeydew present, or 40-100 aphids per leaf (about the size of a 1-2 quarters). Varieties with sugarcane aphid tolerance have a threshold of 80-200 aphids per leaf. Effective materials include Sivanto, Transform, and Sefina.