Sweet Corn
The earliest sweet corn will soon be 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.
Typically, this early flush of moths is fairly susceptible to pyrethroid insecticides. In UD spray trials following recommended spray intervals, pyrethroids have given very good control early, with very little difference among pyrethroids or spray regime. Spray trial results can be found here: https://www.udel.edu/academics/colleges/canr/cooperative-extension/sustainable-production/pest-management/insect-management-reports/. We will begin pyrethroid resistance monitoring at the beginning of June. Please note that we have adjusted some of our trapping locations to be closer to sweet corn.
Thursday trap counts are as follows:
| Trap Location | BLT – CEW | Pheromone CEW |
| 3 nights total catch | ||
| Dover | 3 | 7 |
| Harrington | 0 | 3 |
| Milford/Canterbury | 3 | 3 |
| Rising Sun | 3 | 0 |
| Wyoming | 1 | 2 |
| Bridgeville/Redden | 1 | 3 |
| Concord | 4 | 46 |
| Georgetown | 2 | 4 |
| Woodenhawk | 2 | 2 |
| Laurel | 3 | 63 |
Potatoes
A question came into the office this week of when to expect European corn borer activity in the area for scouting and treating. We have had pheromone traps deployed across the state for several years in a row for ECB but have only caught an occasional moth. This does not necessarily mean that ECB is not a potential threat. However, with the prevalence of Bt field corn in our area, populations are nowhere near where they once were. Southern New Jersey is reporting European corn borer activity, albeit at very low levels. If you are in an area where there is relatively little Bt field corn and you have experienced ECB injury in the recent past, be sure to scout for egg masses under leaves in the lower portion of the canopy or signs of larval infestation. Excellent materials for controlling ECB include Vantacor, Exirel, Besiege, Elevest, and Minecto Pro; Radiant and Blackhawk; and Avaunt. All of these materials will also control Colorado potato beetle. Leafhoppers are active in low numbers across the area and should be scouted for. Leafhoppers are most susceptible to pyrethroids and neonicotinoids, and may still be suppressed by in-furrow neonics. The pyrethroid component of Besiege and Elevest will control leafhopper.
Eggplant
Scout for flea beetles, especially with the cooler weather we have experienced. Colorado potato beetle have been reported from eggplant, and as we move into June, we will need to start paying attention to spider mites, which love eggplant.
Tomato
Be aware that stink bugs are typically our most important pest of early tomatoes. Once green fruit are present, stink bugs can be scouted for by shaking plants or monitoring fruit damage, but the number of samples required may be prohibitively great. So far, stink bug activity in our black light traps has been light. Of the neonicotinoids, only dinotefuran has good to excellent activity on stink bugs. Of the pyrethroids, only bifenthrin has fair to good activity on brown stink bugs.
Cucurbits
Continue scouting for striped cucumber beetles. We conducted another round of bioassays using beetles collected by Nichole Krambeck from the Salisbury region this week which was fairly similar to the previous week’s in that bifenthrin resulted in about 40-60% mortality, Hero at its high rate resulted in higher mortality, and Mustang resulted in fairly low levels of mortality. At this time, I am hesitant to recommend using any pyrethroids for cucumber beetle management on Delmarva.
Begin scouting for two spotted spider mites. We typically begin finding them moving into fields from weedy edges around the first week of June. We are starting to see low levels of mites moving onto pokeweed. By the end of June, mites often defoliate pokeweed, and it turns a bright yellow and pink color which stands out.
Snap Bean
Bean leaf beetle are active in snap bean. Thresholds are 1 beetle per plant and 20% defoliation. Bean leaf beetle come in many different color and spot patterns but always have a black triangle mark on their wings where they come together. Feeding injury will appear as round to blocky holes in the leaves. They are quite susceptible to pyrethroids.
Snap beans planted at the research station during the previous week experienced significant seedcorn maggot damage. When doing stand counts, pay attention to plants with dead apical meristems where the unifoliates should be growing. Other signs of seedcorn maggot include small plants, plants that are ‘hooked’, and, upon digging, seedlings with swollen stems below ground with a grayish or reddish discoloration.