David Owens, Extension Entomologist, owensd@udel.edu
Melons
Two spotted spider mites are moving into watermelons from field interiors, and a report came in earlier this week that sounded like a potential case of transplants with mites on them being planted into the field. Recommended thresholds are 20-30% of crowns infested with 1-2 mites per leaf. In dry weather, mite populations can quickly ramp up, thus weekly scouting, particularly along field edges and in-field obstacles is recommended. Miticides are either contact or translaminar. Translaminar miticide active ingredients are abamectin, acequinocyl, and etoxazole. DO NOT tank mix these with protectant fungicides, especially chlorothalonil. Among the miticides, abamectin and fenpyroximate have been tested the most and provided the best mite reductions in trials. Caution is advised with abamectin. Pay attention to pollinator protection language on its label. If mites are beginning to show up and bees have not been placed yet, it may be a good option, but if bees have been placed, follow label guidance or switch to a different product. Cody Stubbs and I wrote an in-depth fact sheet on spider mites a couple of years ago which can be found here: https://www.udel.edu/academics/colleges/canr/cooperative-extension/fact-sheets/two-spotted-spider-mite/.
If any fields were not treated for cucumber beetle, they should be scouted for aphids. Look for a sticky-wet sheen on plastic and cupping new leaves. Heavily infested plants may take a very long time to recover.
Squash and Zucchini
Next week, squash vine borer may begin emerging from the soil. Towards the end of next week, you may want to consider beginning to treat for them. Be sure to also scout for squash bug. The threshold is 1 egg mass per plant. Because egg masses are impermeable to insecticides, the first application will kill adults and nymphs present. A follow up insecticide about 10 days later will kill hatched nymphs.
Cole Crops
Diamondback moths are increasing in the area. Thresholds for heading brassicas are low, around 5% infested plants. Keep on a rotation schedule of two active ingredients rotated with each other per 30-day pest window. If you are in an area where diamide resistance has not been documented, this is a good time to incorporate them into your program because of their translaminar and translocation properties allowing greater efficacy given denser canopy than strictly contact materials. Spreader adjuvants can help improve coverage, as does a sprayer setup in which multiple nozzles are oriented in such a way as to treat the entire plant canopy from many different sides.
Sweet Corn
CEW trap counts continue to increase. Last year, Morgan and I wrote a summary of several years work with spray trials which can be found here: https://bpb-us-w2.wpmucdn.com/sites.udel.edu/dist/f/9280/files/2024/01/Sweet-Corn-Ear-Insect-Protection-July-2023-99d6827bbb6c8dd4.pdf
Moth counts continue to rise, but not uniformly. Traps are checked Mondays and Thursdays and the counts are on our website by Tuesday and Friday: https://agdev.anr.udel.edu/trap/trap.php.
Thursday trap counts are as follows:
| Location | Blacklight Trap | Pheromone Trap |
| Dover | 1 | 40 |
| Harrington | 0 | 75 |
| Milford | 0 | 67 |
| Rising Sun | 0 | 4 |
| Wyoming | 2 | 77 |
| Bridgeville | 1 | 15 |
| Concord | 1 | 26 |
| Georgetown | 1 | 6 |
| Greenwood | 0 | 4 |
| Laurel | 0 | 82 |
| Lewes | — | — |
Potato
Continue scouting for Colorado potato beetle and potato leafhopper. Colorado potato beetle thresholds are 50 adults or 200 small larvae per 50 stems. Leafhopper thresholds are 1 adult per sweep or 1 nymph per 10 leaves.
Snap Beans
Scout snap beans for bean leaf beetle, corn earworm, and potato leafhopper. Thresholds for potato leafhopper are 5 adults or immatures per sweep. Bean leaf beetle can be easily controlled at flowering or pin-pod stage with a pyrethroid insecticide. If applying a flowering application, wait until late in the day/evening to reduce pollinator exposure.