David Owens, Extension Entomologist, owensd@udel.edu
Sweet Corn
Continue scouting whorl stage sweet corn for Fall Armyworm. New Jersey reports central Jersey fields above threshold and that pyrethroid efficacy is low. That leaves Avaunt, spinosyns, and chlorantraniliprole as our best armyworm materials. Pay attention to rates, as there are label restrictions on the spinsoyns and diamides how much can total active ingredient can be used in a season.
Earworm counts continue to be unusually low, and not just in our traps but is also a sentiment expressed by specialists in New Jersey, Maryland, Virginia, and North Carolina. We harvested our first spray trial of the year that was on a 4-day spray schedule, and it had depressingly non-existent earworms in the untreated check plots. We did however have quite a bit of sap beetle injury in non-pyrethroid treated plots.
Cucurbits
Striped cucumber beetle and squash bugs are the main pests present in cucurbit plantings. Adult squash vine borer was observed earlier this week in a garden plot in Milton. Weekly pyrethroid application should help control them but may flare aphids. We are starting to see an increase in aphid activity although it is too early to tell how their populations will build. We performed another round of bioassay on cucumber beetles, this time from beetles collected near Lincoln. Brigade had no effect. Most of the Assail treated beetles are lethargic or affected. This chemistry can be a bit slower to kill, as can the diamides (not tested in this assay).
Trap counts from Thursday are as follows:
| Trap Location |
BLT CEW |
Pheromone CEW |
| 3 nights total catch | ||
| Dover | 1 | 25 |
| Harrington | 1 | 33 |
| Milford/Canterbury | 1 | 18 |
| Rising Sun | 1 | 25 |
| Wyoming | 1 | 7 |
| Bridgeville/Redden | 1 | 31 |
| Concord | 1 | 24 |
| Georgetown | 0 | 10 |
| Woodenhawk | 1 | 15 |
| Laurel | 2 | 47 |
| Lewes | – | 8 |
Lima Beans
Scout for tarnished plant bug and stink bug. Thresholds for tarnished plant bug adults (small mottled brown insects about the size of a small fingernail) and nymphs (small, round, green with black spots, about the size of an aphid) is 15 per 50 sweeps. Stink bug thresholds are 7 per 50 sweeps. With stink bug, pyrethroids are recommended. With plant bugs, a couple of other products do a good job including Transform and Beleaf. Of all the bug materials, Beleaf is the only one that will not impact pollinators or beneficials, but it will not control stink bugs.
Scout also for worms. Earworm activity in pheromone traps so far is low, but moths will be attracted to the blooming fields to feed. Soybean looper populations are present in Delaware at low numbers. Unlike in soybean, looper in lima bean can destroy pods. We have a wide range of materials that are effective on earworm, but for looper, Intrepid, Avaunt, and the spinosyns are going to have the best efficacy.
Pepper
This is the time of year in which aphid populations begin increasing. Look under leaves and look for signs of honeydew, particularly on fruits. Fields that have been treated previously with a pyrethroid are at greater risk for aphid build up.
Scout also for beet armyworm. Females lay egg masses which result in a few, heavily damaged plants in an area until larvae disperse. They make silken webbing as well. If you start seeing significant defoliation (greater than 10%), you may want to consider a worm material. Please keep in mind that beet armyworm are resistant to pyrethroid insecticides.
Cole Crops
Harlequin bugs are extremely active right now. The typical worm complex is active. In Georgetown, imported cabbageworm, diamondback moth, and cross striped worms are active. If your field has pigweeds in it, be sure to scout for beet armyworm as well. Imported cabbageworm and beet armyworm are both green, but imported cabbageworm will have a velvety appearance and beet armyworm will be smooth with a small black spot right behind the head.