David Owens, Extension Entomologist, owensd@udel.edu
Sweet Corn
Trap counts are fluctuating quite a bit, with some locations higher and others fairly low. This time of year, and particularly with the hot weather we have had, we have had even low trap counts result in a large percentage of damaged ears in untreated check plots. If the daily temperature is above 82 degrees, I advise that spray schedules be tightened 1 day.
Trap counts from Thursday are as follows:
| Trap Location | BLT – CEW | Pheromone CEW |
| 3 nights total catch | ||
| Dover | 2 | 75 |
| Harrington | 0 | 31 |
| Milford | 2 | 51 |
| Rising Sun | 1 | 43 |
| Wyoming | 0 | 21 |
| Bridgeville | 1 | 39 |
| Concord | 3 | 28 |
| Georgetown | 1 | 14 |
| Greenwood | 0 | 16 |
| Laurel | 4 | 68 |
| Seaford | 7 | — |
| Lewes | — | — |
| Millsboro | 3 | 12 |
Brassicas
Fall brassicas are either just transplanted or soon to be transplanted. Scout seedlings and new transplants for worm damage. Active worms include the various armyworm species in addition to imported cabbageworm, cabbage looper, and diamondback moth. Thresholds for young plants is 20% infestation. Adjust your spray pattern such that spray is getting sideways to the undersides of leaves. Use adjuvants to help spread the droplet out on the waxy leaf surfaces. If using Radiant or a diamide (Coragen, Exirel, Harvanta), do not use a sticker. As much as possible, use a treatment window approach alternating among two modes of action during the first generation (roughly 30 days) followed by completely different modes of action. Save broad spectrum materials (Lannate, Orthene, Dibrom, pyrethroids) for later in the season. I have heard that the combination of a pyrethroid + organophosphate can result in some synergism for certain pests, but not sure if this holds true for diamondback moth. Also check your labels to ensure that your selected insecticide is indeed labeled for the particular crop. Many labels exclude certain cole crops. For example, Orthene is only labeled for Brussels sprouts and cauliflower.
Tomato
Corn earworm and yellow striped armyworm are active in tomatoes, and I have seen quite a few worm damaged tomatoes recently. Use high water volume, high pressure, and multiple nozzles aimed at the sides of the row to ensure good coverage. We have a plethora of ‘worm’ materials labeled for tomato, including Entrust and Radiant, Proclaim, Bt (best on small worms but has very little residual), Rimon, Intrepid, Avaunt, and diamides Coragen and Exirel). Stink bugs and leaf footed bugs are also a threat in tomato, if you have to battle them, there are several good premix options that combine a pyrethroid and a neonicotinoid. The neonic component will not affect worms. Among the pyrethroids, bifenthrin is generally thought to be the best for stink bugs, while recent tests in sweet corn show beta cyfluthrin to be a good pyrethroid for corn earworm. Venom and Scorpion are also very effective stink bug products, but will not target worms. The vegetable guide also lists Voliam Flexi which has a neonic and a dimaide.
Spider Mites
Spider mites continue to be active in vegetable fields. They can be pretty hard to dislodge in vegetables on account of frequent fungicide applications and broad spectrum insecticides targeting other pests. Rotate among product modes of action, use high pressure, and an appropriate adjuvant for the material (no stickers or ‘sticky’ fungicides for translaminar products). Some products take longer to result in a mite population decrease than others.
Guess The Pest is taking a brief hiatus this week. Many thanks to those who have logged guesses. For those of you who have not, there is still time!!!