David Owens, Extension Entomologist, owensd@udel.edu
Sweet Corn
Continue scouting for fall armyworm. An infestation noticed early last week at Carvel now has large worms in it and caterpillars are present deep in the whorl. They will finish their development by early next week. Some reports came in this week of sweet corn that appeared to be infested but no worms were present. Spotted cucumber beetle will also feed on whorl stage sweet corn and cause window-paning. This insect is not an economic threat to sweet corn at this stage. Spider mites may be present in some fields. Although no thresholds have been established for them, if a treatment is deemed necessary to preserve crop quality, we have two true miticides labeled for use on sweet corn: Oberon and Zeal SC. Zeal is labeled for 2-6 ounces, but has a 21 day preharvest interval. Oberon’s PHI is 5 days. Note that neither of these products afford worm control. Among the pyrethroids, we sometimes get short-term mite suppression from bifenthrin.
Corn earworm counts in our pheromone traps checked Thursday are lower than they had been, BUT pay attention to black light trap counts. In several locations, black light trap counts have increased. We sometimes see this pattern and thus recommend paying attention to both types of traps. Occasionally a black light trap will indicate a tighter spray schedule than a pheromone trap. Moth counts from Thursday are as follows:
| Trap Location | BLT – CEW | Pheromone CEW |
| 3 nights total catch | ||
| Dover | 6 | 36 |
| Harrington | 1 | 12 |
| Milford | 4 | 41 |
| Rising Sun | 1 | 31 |
| Wyoming | 1 | 4 |
| Bridgeville | 1 | 15 |
| Concord | 2 | 6 |
| Georgetown | 1 | 11 |
| Greenwood | 2 | 7 |
| Laurel | 6 | 42 |
| Seaford | 0 | — |
| Millsboro | 4 | 5 |
| Lewes | — | 31 |
Watermelon
Spider mites seem to be resurging in a couple of the fields we have been scouting. Continue scouting for hot spots – areas with leaf yellowing, and especially hot spots with irregular leaf browning in the centers. Due to their thickness, watermelon leaves sometimes do not exhibit the stippling that is more characteristic of mite feeding on young or thinner leaves.
Continue also scouting for rind-feeding pests such as cucumber beetles and lepidopteran worms (yellow striped armyworm, corn earworm, beet armyworm, among others).
Winter Squash
Begin scouting for aphids. Melon aphids have started increasing in Georgetown. This pest is often held in check until broad spectrum insecticides, especially pyrethroids, are repeatedly applied to a field. Continue scouting for squash bugs (often the cause of those pyrethroids) and striped cucumber beetle. If both pests are present in damaging numbers, consider using acetamiprid containing products.
Tomatoes
Two spotted spider mites have been very active in tomatoes over the last few weeks. Thresholds developed in North Carolina are 2-4 mites per upper canopy terminal leaflet. With our warm weather, 2 mites is probably a safer level. Consider whether or not your material of choice is translaminar or contact. Contact materials are going to need higher water volume and pressures to force product into canopy and into contact with mites underneath of leaves. Rotate among products to avoid selecting for miticide resistance and resulting decreased efficacy in a follow up application.