David Owens, Extension Entomologist, owensd@udel.edu
Cucurbits
Spider mites are building up along edges of fields. In 2021, spider mite populations peaked in the fourth week of June. Mite thresholds are 1-2 mites on 50% of crown leaves. When selecting a miticide, be sure to check the labels for impacts to pollinators, beneficial mites, and adjuvant requirements (especially on abamectin labels).
In squash and zucchini plants, scout for squash bug and squash vine borer. Squash vine borer should be emerging out of the soil soon. It is a day flying moth that looks somewhat like a wasp. It lays single eggs on leaf petioles or on main vines. Frequent pyrethroid applications should prevent neonates from successfully boring into the vines, but beware that they can also cause aphid flare-ups. In susceptible vine crops, one of the first signs of infestation is a wilting leaf on an otherwise healthy vine. Look for white frass along the main vine.
Squash bugs are also actively laying egg masses. Thresholds are 1 egg mass per plant, but wait to treat until egg masses begin hatching. Eggs cannot be killed by insecticide sprays, but nymphs are very susceptible. Be sure to get good coverage along the base of plants where adults like to hide.
Sweet Corn
Corn earworm counts are steadily increasing in pheromone traps. A four-day spray interval should be sufficient for most locations unless a trap near or adjacent to your sweet corn is capturing more. So far, pyrethroid susceptibility is fairly high in vial tests. Trap counts from Thursday are as follows:
| Trap Location | BLT – CEW | Pheromone CEW |
| 3 nights total catch | ||
| Dover | 0 | 10 |
| Harrington | 1 | 38 |
| Milford | 0 | 35 |
| Rising Sun | 2 | 28 |
| Wyoming | 0 | 1 |
| Bridgeville | 0 | 55 |
| Concord | 0 | 19 |
| Georgetown | 0 | 27 |
| Greenwood | 0 | 36 |
| Laurel | 0 | 12 |
| Seaford | 0 | 0 |
Legumes
Continue scouting for bean leaf beetle and defoliation. Several fields, including one at Carvel have experienced significant defoliation. Stink bug counts are also very high in black light traps. Scout late peas for stink bug activity, especially near wood lines.
Tomatoes
Spider mites are moving into agricultural fields, and tomatoes with fruit present are very susceptible to mites. Thresholds are 2-4 mites per upper terminal leaflet. Be sure to check in multiple locations, especially along field edges. Scout regularly, in favorable weather, mite populations can increase nearly tenfold per week.