David Owens, Extension Entomologist; owensd@udel.edu
Soybean
The primary pest that is active in numerous fields right now is corn earworm. All double crop soybean fields should be scouted. Fields at greatest risk are those that were or are drought stressed and with open canopies, but this is not a guarantee. We have a late-planted field at Carvel planted on 30” centers with low earworm activity and a field planted earlier on 15” centers and with a better canopy that is over threshold. Vial testing indicates that a significant number of moths are somewhat resistant to pyrethroids. Exactly how this translates to field efficacy is less well understood, but states farther south have seen very inconsistent and less adequate field efficacy using pyrethroids alone. Non-pyrethroid options include Besiege, Prevathon, Intrepid, Intrepid Edge, Radiant, Blackhawk, and Steward. Use NCSU’s earworm threshold calculator to help decision making: https://www.ces.ncsu.edu/wp-content/uploads/2017/08/CEW-calculator-v0.006.html. Another pest to keep a wary eye out for heading into September is soybean looper. Low numbers of loopers have been observed in soybean fields in Delaware. This critter starts defoliating from the middle of the canopy and working up. While scouting for earworms and stink bugs, take a moment to pull back the canopy to assess the middles.
Sorghum
Heading sorghum to milk stage sorghum needs to be scouted for corn earworm. Economic infestations have been reported in the region. There is a very good threshold calculator available from Texas A&M https://agrilife.org/extensionento/sorghum-headworm-calculator/. This calculator lets you estimate control cost given your insecticide and application method of choice, grain value, and plant population. Note, large larvae are more difficult to kill and some products may not work as well on them. Other worms present include fall armyworm (difficult to kill with pyrethroids), yellow striped armyworm and true armyworm (easiest to control).