David Owens, Extension Entomologist, owensd@udel.edu
Potatoes
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.
Historically, European corn borer has been an important pest of potatoes, we have not captured a single ECB moth in our 10 blacklight traps or 6 pheromone traps.
Cole Crops
Continue scouting for worms and harlequin bugs. As we approach head formation in spring broccoli, please note thresholds decrease from 30% infested plants to 5%. Theres a wide range of good IPM-friendly materials to choose from for worm pests that will preserve natural enemies. This can be especially important if you are going to have subsequent cole crop plantings in the same locale later this season. Unfortunately, the best treatments for harlequin bugs are pyrethroids and neonics. Pyrethroids are highly damaging to natural enemies.
Eggplant and Tomato
The most important early season pest of eggplant and tomato are flea beetles. They will leave a shot hole feeding pattern in the leaves. The adults are very small, usually dark colored. Suggested thresholds are 2-8 per plant depending on the size of the plant and growing conditions.
Cucurbits
Cucumber beetles continue to move into new plantings, although their intensity seems to have dropped off from just a few weeks ago. At this time, care needs to be taken to ensure treatments do not negatively impact pollinators. If bees are expected within 7-14 days, it might be better not to use a soil neonicotinoid treatment. Foliar sprays would result in less or no residue in flower nectar and pollen. Excellent cucumber beetle materials include acetamiprid, thiamethoxam, and carbaryl. Note that carbaryl is extremely toxic to pollinators and has a tendency to flare mites.
Begin scouting field edges for spider mites. They typically begin moving into fields around the first two weeks of June. Unless a population developed in a greenhouse, the most likely place they will be found first is around field edges bordering weedy areas – field ditches, center pivot points, obstacles such as old cemeteries etc. Along wood lines, take note of any pokeweed growing. This weed is usually one of the first to be heavily infested by mites and will turn a yellow-pink color when mites feed on it. Of the miticides, abamectin has been the most consistent, best performer in UD spray trials, but pay attention to pollinator protection language on abamectin product labels. At this time, if a treatment is deemed necessary, you might only need to treat the borders, depending on how a field is setup and where the mites are located.
Onion
Small grains are drying down, and this is the time of the year when thrips begin moving in large numbers seeking alternative hosts. Thresholds are 2-4 immature thrips per leaf. Immatures tend to concentrate at the base of the leaf in the sheath. Getting good coverage with the alliums can be tricky, twin flat fans tend to work a bit better, and use high gallonage.
Sweet Corn
Our earliest sweet corn may begin silking soon. Be advised that trap counts have risen recently for corn earworm, with some indicating the potential for a 3-day spray schedule, others a 4-day spray schedule and still yet others capturing very low numbers of earworm. Please note we do not typically move our traps, traps adjacent to silking sweet corn may capture more moths at a given farm than our traps indicate. Many thanks to Dick Monaco for checking traps this year. Insect trap counts and thresholds can be found at https://www.udel.edu/academics/colleges/canr/cooperative-extension/sustainable-production/pest-management/insect-trapping/. Traps are checked every Monday and Thursday. Thursday trap counts are as follows:
| Location | Blacklight Trap | Pheromone Trap |
| Dover | 0 | 42 |
| Harrington | 0 | 58 |
| Milford | 0 | 82 |
| Rising Sun | 0 | 3 |
| Wyoming | 0 | 67 |
| Bridgeville | 0 | 7 |
| Concord | 0 | 31 |
| Georgetown | 1 | 4 |
| Greenwood | 0 | 8 |
| Laurel | 2 | 71 |
| Lewes | — | — |
Snap Beans
Continue scouting for defoliating insects and for potato leafhopper. Of the defoliators, bean leaf beetle probably poses the greatest concern because it will scar pods later. Thresholds for potato leafhopper are 5 adults or immatures per sweep.
Squash
Squash vine borer may begin to emerge from the soil by the end of next week. This insect typically emerges around 1,000 growing degree days from January 1. In Georgetown we are at 780 and will probably be between 900 and 950 by next Friday.