David Owens, Extension Entomologist, owensd@udel.edu
Moth counts are increasing. Most recent vial tests indicate a 32% survival rate following a pyrethroid challenge. The good news is that this is slightly lower than some years. In August we have tested 168 moths so far with survivorship being slightly lower in cyhalothrin treated vials and slightly higher in bifenthrin treated vials. In light of resistance, high temperatures, and increasing moth counts, it is advisable to tighten spray intervals by a day when following a pyrethroid, and especially during the first week of silking. Once we get past Sunday, temperatures may cool a bit and we do not have to run as tight a spray schedule. With temperatures in the low to mid-80’s it will take eggs 2.5 to 3 days to hatch.
Fall armyworm continue to be active, and New Jersey is reporting continuing new infestations. As a reminder, if treating for fall armyworm, I suggest not using a diamide, we need to save them for silk sprays.
Check silking corn for aphids. I was in a field earlier this week with scattered low numbers around the ear of early silking corn. If aphids become a concern, inclusion of Lannate or Assail in the spray program should help keep their numbers down.
Tuesday CEW trap counts and UD thresholds can be found here: https://www.udel.edu/academics/colleges/canr/cooperative-extension/sustainable-production/pest-management/insect-trapping/. Many thanks to Dick Monaco, Michael Crossley, and Wilmer Bradley for checking traps and reporting numbers. We also acknowledge the support of Specialty Crop Research Initiative program [grant no. 2023-51181-41157/project accession no. 1031455], from the U.S. Department of Agriculture’s National Institute of Food and Agriculture. Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and should not be construed to represent any official USDA or U.S. Government determination or policy.
Thursday trap counts are below:
| Location | Blacklight Trap | Pheromone Trap |
| Dover | 6 | 34 |
| Harrington | 2 | 55 |
| Milford | 9 | 38 |
| Rising Sun | 8 | 73 |
| Wyoming | 9 | 83 |
| Bridgeville | 2 | 54 |
| Concord | 3 | 54 (2 night) |
| Georgetown | 3 | — |
| Greenwood | — | 71 |
| Laurel | 7 | 62 |
| Lewes | 306 | |
| Milton | 79 | |
| Whaleyville | 82 (Monday) | |
| Newark | 51 (4 nights) |
Cucurbits
The second flight period for squash vine borer has begun. Weekly application of a pyrethroid (helpful for squash bug) or chlorantraniliprole (labeled for loopers) will keep them from getting into the vines. With intensive pyrethroid use, watch out for flaring up aphids. Melon aphid and green peach aphid populations typically peak August to September. If aphids become a problem, and especially if honeydew begins accumulating on fruit, there are a lot of excellent aphid materials labeled, including cyantraniliprole and cyclaniliprole (see note above on chlorantraniliprole).
Pay attention to striped cucumber beetle on winter squash. Their second generation will be emerging soon, although it can be difficult to tell overlapping generations apart. I do not recommend pyrethroids for striped cucumber beetle control.
Tomatoes
Begin treating tomatoes for worms, especially if tomatoes have small fruit and flowers on them. The biggest threat is corn earworm which is resistant to pyrethroids. Use higher volume, higher pressure to drive material into the canopy. Also on younger plants, continue scouting for spider mites and for signs of stink bug. Although CEW is our number 1 pest in late summer/ fall tomatoes, stink bugs can still be a major problem, particularly if using worm-specific material. The threshold for spider mites is 4 mites per upper canopy terminal leaflet.
Cole Crops
I’ve seen quite a few fall brassicas planted recently. Be scouting for worms and match your material of choice to the worm species you have. Diamondback moth and beet armyworm are both active and resistant to pyrethroids. Bt is a good material to use on young plants where it is easier to obtain good coverage. If growing brassicas on the same farm that had brassicas in the springtime, take a look at the products used most recently and switch up modes of action to help delay potential resistance development in your DBM population. Also, we do have a couple of ‘oldie goodie’ broad spectrum materials labeled for various cole crops, as well as pyrethroids and besiege. As much as possible, avoid using them early on. Natural enemies can wipe out DBM and large proportions of the other worm pests when conditions are right and we don’t accidentally kill them off first.