David Owens, Extension Entomologist, owensd@udel.edu
Insecticide Update
UPL now is marketing a new liquid 30SC formulation of Assail: https://www.cdms.net/ldat/ldIFS000.pdf. Pay attention to the label as the rates are a bit different from the granular 30 SG formulation.
Sweet Corn
Scout sweet corn that is near 7 days to preharvest for aphid outbreaks. One was reported earlier this week, aphids had covered the undersides of leaves and ears, leading to excessive honeydew deposition on the ears. Frequent pyrethroid applications flare up aphids by removing natural enemies from fields. Unfortunately, our best earworm protection sprays all contain pyrethroids. Our best aphid materials are Assail and Sivanto Prime. Assail’s lower rates may be used up to 1 day before harvest, while the higher rates and Sivanto Prime both have a 7 day PHI.
Earworm counts are moderate for this time of year but still increasing at many locations. Keep in mind that traps next to silking sweet corn may catch many more moths than our closest trap would indicate, and sometimes there can be quite a bit of within field variation with exact moth catch. With cooler temperatures this week, we shouldn’t need to have tighter spray intervals on account of weather. Earworm counts from Thursday are as follows:
| Trap Location | BLT – CEW | Pheromone CEW |
| 3 nights total catch | ||
| Dover | 3 | 91 |
| Harrington | 1 | 78 |
| Milford | 8 | 108 |
| Rising Sun | 4 | 131 |
| Wyoming | 2 | 46 |
| Bridgeville | 1 | 29 |
| Concord | 1 | 48 |
| Georgetown | 1 | 77 |
| Greenwood | 3 | 23 |
| Laurel | 7 | 71 |
| Seaford | 0 | — |
| Lewes | — | 91 |
Cucurbits
Scout for beet armyworm and corn earworm in watermelon. These two potential rind feeding worms are completely or partially resistant to pyrethroids.
Cucurbit fields previously treated with pyrethroids and not Assail earlier this year may be at risk for high aphid populations. If you see large aphid populations, look for beneficial insect activity. We had heavy aphid pressure in our mite trial this year and dropped a spray trial on top of the aphids. Numerous lady beetle, syprhid maggot and lacewing larvae were present. In 1 week’s time, natural enemies completely annihilated the aphids in my untreated check plot.
Cole Crops
Cross striped cabbageworms and cabbage webworm have both made an appearance in Georgetown cole crop plots. Generally, thresholds are pretty high for worm pests, but some states advise a much lower threshold for cross striped worms: 5% infested plants. This is because their eggs are laid in masses and the caterpillars are voracious. Curiously, cabbage loopers have not been observed yet. This is a species of interest because Torac is less effective on looper. Hot and relatively dry weather recently has resulted in an increase in diamondback moth activity. Remember to use treatment windows to manage DBM, rotating two modes of action within a 1 month period and rotating among two different modes of action during the next month. Last year, beet armyworm was the most common worm pest in our late cabbage trial; we are picking up low numbers of beet armyworm in other crops. Beet armyworm are resistant to pyrethroids.
Pepper
Continue scouting for beet armyworm activity. Caterpillars are being observed in other crops.