David Owens, Extension Entomologist, owensd@udel.edu
Sweet Corn
Third instar and some fourth instar armyworm are present in sweet corn in the state. Begin scouting all whorl stage sweet corn for armyworm infestation. Armyworm can be spotty. Females lay egg masses that can have several hundred eggs. Early stage larvae disperse to nearby plants, leading to circular areas in the field with heavily infested or damaged plants. We have a few options for whorl stage worms that we do not have for silking corn, including Rimon, Intrepid, Intrepid Edge, and Avaunt. Save Coragen, or rather its active ingredient, chlorantraniliprole, for silk sprays. We are limited in how much of the active ingredient we can put out and it is the valuable component in Besiege.
Trap counts continue to be light and application intervals may be longer than before. Recently some folks have commented about seeing sap beetles in corn that was not sprayed heavily but was sprayed with pyrethroid. Insecticides will not ‘cure’ an already infested ear. If you have a history of sap beetle or if you have cull piles of other vegetables in nearby vicinity, you are at elevated risk for them. Lannate, when applied at full silk, should help control sap beetles. Carbaryl is prohibited on hand harvested corn and is hard on bees. Nearby beekeepers should be notified of any carbaryl applied, and you should probably wait until corn is no longer shedding pollen to apply.
We tested 10 moths this week for pyrethroid resistance, with survivorship at 20%. Thursday moth counts are as follows:
| Trap Location | BLT – CEW | Pheromone CEW |
| 3 nights total catch | ||
| Dover | 2 | 31 |
| Harrington | 0 | 38 |
| Milford | 1 | 3 |
| Rising Sun | 0 | 24 |
| Wyoming | 1 | 2 |
| Bridgeville | 0 | 4 |
| Concord | 0 | 8 |
| Georgetown | 0 | 0 |
| Greenwood | 0 | |
| Laurel | 2 | 18 |
| Seaford | 1 | 3 |
| Lewes | 0 | 3 |
| Millsboro | 2 | 2 |
Peppers
Beet armyworm is active in the area. Scout peppers for defoliation. Beet armyworm is resistant to pyrethroids, but we have many other excellent worm materials from 8 different modes of action. I am starting to see winged aphids in other vegetables. Pyrethroid use can result in aphid outbreaks, so scout accordingly.
Melons
All major arthropod pests are active in melons. Cucumber beetles continue to emerge from the soil. Despite last week’s rain, mites have been enjoying recent heat and populations are increasing in many fields. Beet armyworm was spotted in pigweed in a melon field early this week, and leafroller scarred up some melons in one of my plots. Intrepid and Radiant are good worm materials for worms. Intrepid should be used on small larvae. Radiant will move into leaf tissue and have good residual activity. Diamides are excellent worm materials with long residual activity, and premixes are available that will control either mites or beetles. Harvanta and Exirel will impact cucumber beetles. Minecto Pro is a premix containing cyantraniliprole and abamectin and will control mites too, but pay attention to bee caution language. Gladiator is a premix of a pyrethroid and abamectin and may help with beetles. Besiege is a premix of a diamide and a pyrethroid. Assail still provides very good control of beetles.
Cole Crops
Late season cole crops will be going into the ground soon. This summer so far has been warm and relatively dry, setting us up for higher populations of diamondback moth this fall. Review your worm management plan, and be sure to scout carefully after application. Diamondback moth is notorious for developing resistance to multiple modes of action. Resistance should be fairly localized as these are not strong fliers. Rotate modes of action within a 30 day window before switching modes of action. Avoid using pyrethroids or organophosphates if possible until near the end of the fall to preserve beneficial insect activity.