David Owens, Extension Entomologist, owensd@udel.edu
Cucurbits
Cucumber beetles continue to move into watermelons, cantaloupes, and other cucurbits. The infestations that I have seen tend to be fairly localized, but intense. While beetles do not transmit bacterial wilt to watermelon, heavy feeding can make the plant more vulnerable to gummy stem blight. Thresholds range from 2 to 5 beetles per plant in watermelon. If you need to control beetles and are within a week or two of honeybee placement, it may be a good idea to switch to foliar sprays of Assail, pyrethroid, or diamide insecticide. Some folks have commented that pyrethroid efficacy can be variable. Diamides can be expensive, and while they quickly stop beetle feeding, they do not kill beetles quickly.
Sweet Corn
Some of the first sweet corn is getting near to tassel push or has started silking. For tassel push sweet corn, scout for worms infesting the whorl. While CEW activity seems to be light so far, their first generation into corn whorls can occasionally cause issues. Whorl stage corn thresholds are fairly high, between 15 and 30% whorl infestation. Tassel-push corn thresholds are 15%. We have a couple of different options for pre-silking sweet corn for worms that we do not have in silking corn, namely Avaunt (WDG and eVo formulations) and Intrepid or Intrepid Edge.
Moth activity has increased. Historically, we get a mid to late June small peak. We caught a single European corn borer in the Wyoming area.
Insect trap counts are as follows:
| Trap Location | BLT – CEW | Pheromone CEW |
| 3 nights total catch | ||
| Dover | 1 | 1 |
| Harrington | 1 | 0 |
| Milford | 1 | 1 |
| Rising Sun | 1 | 0 |
| Wyoming | 1 | 0 |
| Bridgeville | 1 | 0 |
| Concord | 3 | 21 |
| Georgetown | 0 | 1 |
| Greenwood | 1 | — |
| Laurel | 2 | 4 |
| Seaford | 0 | 0 |
Potato
Continue scouting field interiors. With recent hot weather, adults are capable of flight and will begin moving in from the edges.
Brassicas
Continue scouting for worms, especially as heads are nearing harvest. Thresholds decrease to 5% infested plants as they form heads or harvested structure. You can find more information in the Mid-Atlantic Vegetable Production Guide: https://www.udel.edu/content/dam/udelImages/canr/photography/extension/sustainable-ag/NFP-2020-F-Cole-Crops.pdf.