David Owens, Extension Entomologist, owensd@udel.edu
Cucurbits
The main pests that are active right now are spider mites, cucumber beetles, and rind worms. Spider mite activity may have lessened this week, check for active mite populations. Stippling doesn’t go away from earlier infestations. Most of our crops are well into the reproductive and harvest stages, mites can more easily take advantage of the plants but also the canopy is more robust and can tolerate more mites. Check leaves further out on vines.
Cucumber beetle thresholds are 2 beetles per plant for watermelon. You may want to use lower thresholds for pumpkins and for cantaloupe. Acetamiprid is the best cucumber beetle material. Rindworms are active. Some, like yellow striped armyworm and corn earworm, focus their attention on blossoms, but if they get onto fruit can cause significant scarring quickly. Others, like leaf rollers and loopers, will be on leaves and rinds. Beet armyworm can also be present, but prefer pigweed.
Sweet Corn
Scout for fall armyworm NOW. New Jersey is reporting increasing fall armyworm infestation, with some sites over the 30% mid-whorl stage infestation threshold. Reports came in this week of infestation levels between 15-30%. I strongly recommend not using a diamide insecticide if targeting FAW. Non diamide options include Lannate, Avaunt, Radiant, and Intrepid Edge. Sweet corn in whorl stage now will face the greatest earworm pressure. We need to save as much chlorantraniliprole (Coragen, Vantacor, Shenzi, Besiege, Elevest) that we are allowed to use for silk sprays.
We completed another round of vial tests recently and moth survivorship has risen to 35%, this is greater than earlier this season. Moth counts have remained steady. I recommend tightening spray timing by a day if the following conditions are met: sweet corn has been silking less than 10 days, temperatures are greater than the low 80s, and the previous application was a pyrethroid alone or a pyrethroid + Lannate.
Thursday moth counts are as follows:
| Location | Blacklight Trap | Pheromone Trap |
| Dover | 1 | 47 |
| Harrington | 1 | 65 |
| Milford | 0 | 26 |
| Rising Sun | 1 | 32 |
| Wyoming | 2 | 36 |
| Bridgeville | 0 | 42 |
| Concord | 1 | 34 (M-W) |
| Georgetown | 0 | — |
| Greenwood | 0 | 68 |
| Laurel | 2 | 70 |
| Whaleyville | — | 68 |
| Lewes | 37 (S-W) |
Fruiting Vegetables
Continue scouting for stink bug injury and spider mites. Our main corn earworm flight has not yet begun, but any field that has open flowers now should be protected against worms. Spider mite thresholds are 2-4 mites per upper canopy terminal leaflet. If a field has stink bug injury, the best materials contain dinotefuran (ex. Scorpion, Venom) or bifenthrin (ex. Brigade, Hero).
Also keep an eye out for Colorado potato beetle, especially in eggplant!!!