David Owens, Extension Entomologist, owensd@udel.edu
Sweet Corn
Numerous reports have come in of earworms in sweet corn tassels, and even one report of a few European Corn Borer in tassels. The Vegetable Production Recommendations guide uses a threshold of 15%; New Jersey uses a threshold of 12% infested tassels. Tassel-exposed worms should come into contact with a greater amount of active ingredient which may help overcome the drawback of targeting a larger worm. We have multiple control options, but I advise saving chlorantraniliprole, if at all possible, for silk sprays. Many of the sweet corn farms where we have traps are on a 3-day spray schedule.
Generally, insecticide resistance is lower during the beginning of the season and worms are easier to control with pyrethroids. We have begun vial testing and our standard dose, 5 ug of Cypermethrin, had 14.3% survivorship, which is fairly low. This is good. We tested bifenthrin, lambda-cyhalothrin, and beta-cyfluthrin last year to determine which would be the most appropriate doses in vial testing, and preliminary vial tests run last week returned similar results to our spray trials which fewer moths surviving beta-cyfluthrin and more moths surviving lambda-cyhalothrin.
A report came in from New Jersey of aphids in tasseling sweet corn. With frequent pyrethroid applications, it is possible to flare up aphid populations. Lannate will have corn leaf aphid activity, but last year we observed a heavy infestation of melon aphids on sweet corn. Melon aphids are much less susceptible to methomyl than other aphids. Assail and Sivanto are labeled for sweet corn. Assail will also have some sap beetle activity. Assail has 2 different rates, aphid rates are lower and have a 1-day PHI whereas the rate for other insects is as high as 5.3 oz but with a 7 day PHI.
Thursday Trap Counts are as follows:
| Trap Location |
BLT CEW |
Pheromone CEW |
| 3 nights total catch | ||
| Dover | 1 | 71 |
| Harrington | 1 | 16 |
| Milford/Canterbury | 0 | 140 |
| Rising Sun | 0 | 63 |
| Wyoming | 1 | 3 |
| Bridgeville/Redden | 0 | 3 |
| Concord | 1 | 37 |
| Georgetown | 0 | 15 |
| Woodenhawk | 0 | 22 |
| Laurel | 1 | 119 |
| Lewes | — | 50 (2 nights) |
Cucurbits
Continue scouting for spider mites in watermelon and cantaloupe. Spider mite threhsolds are 50% infested crown leaves with 1-2 mites per leaf. This also suggests a degree of a sliding scale to take hotspots into account. Mites will generally be concentrated around field edges or other in-field obstacles or features such as drainage ditches, pivot points, old cemeteries, etc.
Kentucky is reporting squash vine borer is now active, and we have accumulated enough degree days here for them to be active as well. On pumpkins and summer squashes, begin weekly pyrethroid, chlorantraniliprole, or combo application concentrating sprays along the stem or even as high as the leaf petioles. If you begin treating, scout fields regularly to make sure aphid populations are not exploding.
Potatoes
Continue scouting for Colorado potato beetle and potato leafhopper.
Snap Beans
The earliest planted snap beans are beginning to flower. Corn earworm activity is moderate to high in sweet corn and snap beans may benefit from an insecticide somewhere between pin and full pod. A chlorantraniliprole (Vantacor, Besiege, Elevest) application should provide long enough residual to keep the crop worm free. Scout for potato leafhopper on vegetative stage snap beans, particularly if a field did not have a neonic seed treatment on it.