David Owens, Extension Entomologist; owensd@udel.edu
Soybean
The usual defoliator complex is active. Dectes numbers seem to be decreasing. Spider mites are still active. When scouting for them, be sure to put them under magnification to check if they are alive or dead. The cool front 10 days ago brought weather that favors fungal pathogen outbreaks which usually occur about 14 days after. This is not a guarantee, as aside from that rain event and a small one recently, it’s been plenty hot and dry.
There have been reports of some field corn fields around Kent Co. with large numbers of earworm. When those caterpillars finish developing, the adults will be looking for drought stressed, open canopied, flowering soybean. Our August peak moth flight is just beginning, be scouting for larvae in the coming weeks. If a field goes above threshold and requires treatment, be cautious with pyrethroids. We have been seeing a significant number of moths survive our testing, and other states further south have been seeing inconsistent to poor control. That doesn’t mean you won’t get sufficient kill, but it’s not going to be as reliable. Other excellent materials labeled for CEW include Prevathon, Steward, Radiant, and Blackhawk. As a reminder, a very useful tool for calculating thresholds depending on sampling method, row spacing, estimated control cost, and soybean value can be found here: https://soybeans.ces.ncsu.edu/wp-content/uploads/2017/08/CEW-calculator-v0.006.html.
Sorghum
Any fields that are pushing heads or flowering will be attractive to corn earworm to lay eggs in. During the next few weeks be sure to check heads for earworm. One earworm per head can reduce yields by about 5%. When scouting, take a 5 gallon bucket to beat heads into, 5 heads per spot, 10 spots per field and count the number of dislodged earworms.