David Owens, Extension Entomologist, owensd@udel.edu
Sweet Corn
The earliest sweet corn is now silking. As a general reminder, thresholds for silking sweet corn can be found on the Insect Trapping webpage: https://www.udel.edu/academics/colleges/canr/cooperative-extension/sustainable-production/pest-management/insect-trapping/. The last time I looked, the links for action thresholds for snap beans and sweet corn had been inadvertently switched. It is important to look at both black light and pheromone trap counts. There are occasions when the black light traps will indicate a more conservative spray schedule than pheromone traps.
Trap captures have climbed significantly in southern Sussex County and at some sites, a 3-day spray schedule is indicated but at most sites a 4 day spray schedule should be sufficient. With cool temperatures (and especially cool nighttime temperatures) and the usual pattern of higher moth susceptibility to pyrethroids, there is no need to go more conservative on spray intervals. Our most recent, earliest trials have been under low moth population environments in late June to early July and there is very little difference among pyrethroids or spray programs in terms of efficacy. The situation is very different late in the season. Many thanks to Dick Monaco for checking traps on Mondays and Thursdays. Thursday trap capture data is as follows:
| Trap Location | BLT – CEW | Pheromone CEW |
| 3 nights total catch | ||
| Dover | 1 | 5 |
| Harrington | 1 | 9 |
| Milford/Canterbury | 1 | 44 |
| Rising Sun | 1 | 27 |
| Wyoming | 1 | 0 |
| Bridgeville/Redden | 0 | 1 |
| Concord | 1 | 38 |
| Georgetown | 0 | 12 |
| Woodenhawk | 0 | 8 |
| Laurel | 3 | 99 |
| Lewes | — | |
Cucurbits
Typically I see my first spider mites entering watermelon fields during the first two weeks of June. A report came in this week of spider mites in low numbers around the edges of at least 1 field. Based on research conducted by UD entomology master’s student Cody Stubbs, unless a field has infested transplants, mites almost always come in from around edges, particularly weedy ditch banks and wooded edges. Concentrate scouting efforts to these locations. In spray trials over the last several years, abamectin has been the most effective and consistent miticide, but it is hard on pollinators and has pollinator protection stipulations on labels of products containing the active ingredient. Another implication of Cody’s research is that border applications of abamectin could effectively delay mite migration into fields while at the same time, minimizing effects on honeybees and other pollinators.
Snap Beans
Continue scouting for defoliators such as bean leaf beetle and potato leafhopper.
Tomato
Stink bugs are the most severe early tomato pest. Compared to last year, stink bug activity in our blacklight traps is right now much, much lower. Thresholds and sampling for live stink bugs on clusters of tomato can be a bit difficult. If you are in an area that has experienced severe stink bug damage previously, you might want to consider Hero, bifenthrin, or dinotefuran (Scorpion or Venom).
Cole Crops
Diamondback moths continue to be very active in plantings. Remember to use high water volume, higher pressure and multiple nozzles per row to get as much coverage as possible. Early planted cabbage is cupping now which means lower thresholds should be used. At this point, Bt is less likely to be as effective given the greater amount of leaf area to be protected and the difficulty of getting as good of penetration into the developing head.
Potatoes
Low numbers of Colorado potato beetles were observed in potato fields again this week. Thresholds are 50 adults per 50 stems, 200 small larvae, or 75 large larvae. If a neonicotinoid was used at planting, use a different mode of action.