David Owens, Extension Entomologist, owensd@udel.edu
Sweet Corn
Corn earworm trap catches are in parts a bit on the higher side. Wet weather (finally) is also going to complicate treating. Last year we had a trial in which shortly after the corn was treated, we irrigated with overhead irrigation and once the leaves dried from that, treated another set of plots with the identical sprays. There was a significant drop in efficacy. As soon as you are able, it may be worthwhile to treat the field again.
A report came in of spider mite activity in sweet corn. We saw this last year as well, but spider mite activity this year has been considerably greater. There are 3 options for dealing with mites: Oberon (5 day pre harvest), Zeal (21 day pre harvest), and multiple bifenthrin applications. Oberon and Zeal tend to have greatest effect on sterilizing females and/or destroying small nymphs. This may allow a significant population to persist for a time. Bifenthrin does have miticidal activity, but its not as strong and does not last. It is most effective on knocking down adult mites. Bifenthrin can be applied twice, the good news with it is that it is among the better pyrethroids for corn earworm management. There is also a pre-mix formulation with chlorantraniliprole, Elevest, which provides excellent worm protection. If you are worried about mites, it may be a good idea to incorporate two bifenthrin applications early in the spray program. The weather has also been good for aphids; acetamiprid is labeled for sweet corn and should provide good aphid control. Remember, Lannate is not effective on melon aphids. There are also a couple of bifenthrin/acetamiprid pre-mixes.
Thursday trap captures are below. You can find our thresholds and trap counts from various links off this main landing page: https://www.udel.edu/academics/colleges/canr/cooperative-extension/sustainable-production/pest-management/insect-trapping/. Pay attention also to blacklight trap captures, thresholds are much lower for blacklights, meaning only a handful would trigger a given spray timing.
| Location | Blacklight Trap | Pheromone Trap |
| Dover | 2 | 34 |
| Harrington | 2 | 73 |
| Milford | 4 | 15 |
| Rising Sun | 0 | 7 |
| Wyoming | 6 | 88 |
| Bridgeville | 1 | 11 |
| Concord | 4 | 12 (2 nights) |
| Georgetown | 0 | 12 (2 nights) |
| Greenwood | 1 | 24 |
| Laurel | 1 | 58 |
| Whaleyville | — | 8 |
Cucurbits
Striped cucumber beetles are continuing to emerge out of the soil. Assail is our best product targeting cucumber beetles; pyrethroid efficacy is questionable. We also have carbaryl but it is highly toxic to pollinators. Carbaryl can also have good efficacy on worms. Harvanta is an excellent worm material that also has decent beetle activity; it can be slower to kill. Reports have been coming in of various worm species in melons, and especially of corn earworm feeding on flowers. It is only a matter of time before it transitions to eating fruit rinds.
Mites continue to be a major headache, hopefully this rain will help slow mite reproduction down. At this time, our thresholds switch to looking at mites on vine terminals. If half of them have mites, a spray is called for.
Solanaceous Crops
Scout for second generation Colorado potato beetle in eggplant and tomato. In tomato, stink bugs are historically the most important pest until August’s influx of corn earworm. Scout for beet armyworm defoliation in the peppers and stink bug activity.