David Owens, Extension Entomologist; owensd@udel.edu
Soybeans
Continue scouting for stink bugs. We sampled more fields this week in Kent County and still have not found an economic infestation of them, so I suspect their populations are lower this year. Podworm populations are relatively light in our trapping network with the exception of our Laurel and Concord traps which are indicating a high to very high population. Scout any double crop beans R3 or younger for podworm, especially in SW Sussex!
If you run into podworm, take a look at NCSU’s CEW threshold calculator: https://go.ncsu.edu/cewthreshold. Throwing in some ballpark estimates for soybean, a control cost of $20 (10 for application, 10$ for product), keeping the bean price at 10 and a 14-inch row space, I get an economic injury level of 3 CEW per 15 sweeps. In years where the value of bean is higher, that number would be 2. If the control cost is 25, the EIL is 3.6; if your row spacing is 7 inches, add another 0.1 earworm.
In the last several years of our testing, the best products contain chlorantraniliprole. The lowest rate of Besiege or Vantacor has performed excellently. Denim is also a good material, be aware that it is a much higher toxicity than the others. The main reason I mention it is that it is excellent on soybean looper. SL is a hard to predict critter here, we’ve had as many as 2-3 per 15 sweeps in Georgetown, which is a bit high, but not concerning.
Sorghum
As a general reminder, our sorghum insect control fact guide can be found here: https://www.udel.edu/content/dam/udelImages/canr/pdfs/extension/sustainable-agriculture/pest-management/InsectControlinSorghum-2020-updated.pdf. There is a detailed section on sugarcane aphid which are active in our area. What is not in the guide is anything about corn leaf aphid. There are no established thresholds for CLA. It is a dark, bluish green, rectangular aphid that is common on upper whorl leaves, boot, and flag leaf. You will also see the white cast skins from previous molts. Typically, a fair number of plants can be infested, up to 20%, but their populations crash as the head emerges. If there are more than that, they are visibly holding the plants back, the leaves becoming discolored, and aphid populations are still present in high number with few winged aphids, then might a treatment be considered. This is rare. Sugarcane or sorghum aphid is whitish-yellow and present on the underside of mid-canopy leaves.