David Owens, Extension Entomologist, owensd@udel.edu
Corn
Continue scouting for stink bug and cutworm activity, particularly in late planted, late burn-down fields. Cutworm are large enough to cut plants, and we experienced a significant cutworm flight earlier this year in our Smyrna and Middletown traps. This does not necessarily mean that a given field in those areas will have cutworm or that a given field outside of those areas will not. Cutworm are attracted to weedy fields to oviposit.
Soybean
Reports continue to come in of slug damage, particularly in norther Delaware and adjacent areas in Maryland where ground is heavier. It is extremely important to make sure seed slots are closed. With the relatively dry weather recently, turbo tillage, vertical tillage, or strip tillage should all provide sufficient reduction in slug activity around the furrow. Slug bait is an option, and should be considered if, after planting a field with a high number of slugs in it the seed slots did not close well. Open seed slots are going to concentrate slugs around the seed as they seek moisture and shelter, making a delayed rescue treatment problematic. If applying bait, you will want to achieve 5-6 bait pellets per square foot. Remember, provided that a field is irrigated, even stand counts as low as 70,000 can provide a good yield.
Grasshopper nymphs are hatching out of the soil. Grasshoppers are frustrating pests to make recommendations on. Nymphs tend not to feed much on plants, but their defoliation level gradually increases until reaching potentially concerning levels in mid-late July, at which time they are larger and a bit more difficult to control. Remember, defoliation thresholds are fairly high, at 30% during vegetative stages and 20% during reproductive stages. Other thresholds used (https://soybeanresearchinfo.com/soybean-pest/grasshoppers/) are 30-45 nymphs per square yard. We conducted a spray trial in 2020 with various products. Elevest at a mid-rate provided greater knockdown than pyrethroids alone, followed by dimethoate and a low rate of Prevathon. Please note that Prevathon has been replaced by Vantacor recently. If using a pyrethroid, use the high label rate.
Other defoliators active now include bean leaf beetle and various members of the defoliating worm complex.
Wheat
Low numbers of true armyworm have been reported this week feeding in wheat. Thresholds are 1-2 larvae per linear foot or 3-5 per square foot. It is important to examine ground residue as well because they generally like to hide during the day. At this point, our only pyrethroid control option is Mustang due to its relatively short pre-harvest interval of 14 days.
Early Season Moth Trapping
This is the last week of trapping for true armyworm and black cutworm. Many thanks to Joanne Whalen and Haley Sater (UMD extension) for assistance with traps and to the 5 farmers who hosted our traps near their telephone poles.
| Location | # of Nights | Total Catch | |
| TAW | BCW | ||
| Willards, MD | 5 | 0 | 0 |
| Salisbury, MD | 7 | 0 | 4 |
| Seaford, DE | 7 | 0 | 0 |
| Sudlersville, MD | 7 | 0 | 8 |
| Harrington, DE | 7 | 15 | 7 |
| Smyrna, DE | 6 | ||
| Middletown, DE | 6 |
Alfalfa
Scout for potato leafhopper. Thresholds per 100 sweeps can be found here: https://www.udel.edu/content/dam/udelImages/canr/pdfs/extension/sustainable-agriculture/pest-management/Insect_Control_in_Alfalfa_-2023.pdf.