David Owens, Extension Entomologist, owensd@udel.edu
Sweet Corn
This is the last pheromone trap and blacklight trap update of the 2023 season. Many thanks to Dick Monaco for checking traps every Monday and Thursday since May, and Morgan Malone for entering trap counts online. Thanks to DDA for supporting the trapping network via specialty crop block grant funding this year.
Counts are coming down in both pheromone and blacklight traps and are considerably lower than 2 weeks ago. Sites though where the pheromone trap would indicate a 4-day spray schedule, blacklight traps still indicate a 3 day. With cooler temperatures, a 3-day spray schedule even following a pyrethroid should be sufficient.
Thursday trap counts are as follows:
| Trap Location |
BLT CEW |
Pheromone CEW |
| 3 nights total catch | ||
| Dover | 3 | 155 |
| Harrington | 3 | 64 |
| Milford/Canterbury | 4 | 75 |
| Rising Sun | 6 | 71 |
| Wyoming | 2 | 28 |
| Bridgeville/Redden | 3 | 33 |
| Concord | 4 | 51 |
| Georgetown | 4 | 33 |
| Woodenhawk | 3 | 74 |
| Laurel | 9 | 47 |
Tomatoes
Continue with regular worm treatment, especially any tomatoes that still have flowers on them. Even though most of the earworm in our plots are large worms getting ready to cycle out, there are still a few small stragglers. Remember, high volume and pressure will help get adequate material to worms deep in the canopy.
Legume Vegetables
Corn earworm, soybean looper, and stink bugs are all still potential threats. Soybean looper is a defoliator in edamame but will carve out small lima bean pods. It is difficult to kill. Southern states generally recommend Intrepid Edge or Steward. In a 2020 soybean spray trial, of the generally recommended products, Steward performed the best. The vegetable version is Avaunt eVo. In 2020, Lannate knocked them back a little more than 50-60%. The 2020 trial was conducted September 17. Previous diamide use may help suppress them somewhat.
Cole Crops
Continue scouting for worms, aphids, flea beetles and harlequin bugs. Most of the aphids we have seen thus far have been green peach aphid, but cabbage aphids are beginning to increase. Green peach aphid is resistant to pyrethroids. You can find an efficacy rating chart put together by Tom Kuhar here: https://www.udel.edu/academics/colleges/canr/cooperative-extension/fact-sheets/insecticides-aphid-control/. Be sure to look at the worms carefully. At least in Georgetown, the most common worms present are imported cabbageworm, beet armyworm, and cross striped worm, with a few diamondback moths as well. Beet armyworms are resistant to pyrethroids. Diamondback moth populations tend to be local, so if cole crops were grown in the area previously, take product application history into account when selecting control materials so as to not over-rely on any particular mode of action. Avoiding pyrethroid, carbamate, or organophosphate sprays helps preserve natural enemies which can put a severe hurting on the worms. Thresholds are 30% infested plants during vegetative stages but decreasing to 15% at beginning of cupping/curd formation and then down to 5%. Cross striped worms have their own threshold: 5% infested plants. This is because moths lay egg masses which lead to numerous, ravenous caterpillars on a single plant.