David Owens, Extension Entomologist, owensd@udel.edu
Soybeans
Scout double crop soybean for corn earworm beginning next week. Our flight has just begun, and earworms are liable to show up in double crop soybean anytime in the next 3 weeks. Corn earworm prefers drought stressed plants, open canopies, and flowers. We do not have drought stress right now, and recent rains may help increase pathogen loads and blunt some of the potential population, but do not count on it. The best treatment is Besiege or Elevest applied at their low rates. Last year when populations spiked to near 1 earworm per sweep, Besiege at 6.5 fl oz zeroed them out. Earworm thresholds are generally around 2-3 worms per 15 sweeps. You can find NCSU’s earworm threshold calculator here: https://www.ces.ncsu.edu/wp-content/uploads/2017/08/CEW-calculator-v0.006.html.
If green stink bugs are in a field above threshold of 5 bugs per 15 sweeps or 2.5 bugs per 15 sweeps and 1 earworm per 15 sweeps (half threshold of both species), a treatment is justified. Remember, green stink bugs are susceptible to pyrethroids whereas brown stink bugs are much less sensitive to pyrethroids. Of the pyrethroids, bifenthrin does the best job.
Sorghum
We captured our first sugarcane aphid last week in a field near Lewes, DE. Scout late sorghum regularly until it is in the soft dough stage to make sure large populations are not building up (20-30% infested plants with isolated areas of honeydew present).
Late sorghum that has not headed or is in early pollen shed is at risk for damaging earworm populations and fall armyworm. Thresholds for whorl stage fall armyworm is high and most likely will not be reached. However, fall armyworm and earworm should be treated the same when in heads. Texas A&M has an excellent threshold calculator and guidance here: https://extensionentomology.tamu.edu/sorghum-headworm-calculator/.