Vegetable Crop Insect Scouting

David Owens, Extension Entomologist,

Colorado potato beetle are becoming active. Adults cannot fly in temperatures below 80 °F, this is why beetles are concentrated on edges of fields right now, but that may change with the current warmth. It has also been close to 8 weeks since planting, about the time that neonicotinoids start wearing off. When scouting, look at 5 stems from 10 locations in the field. Do not concentrate sampling just on the edges unless you intend to only make a border application. Treatment is generally advised if finding 50 adults, 75 large larvae, or 200 small larvae per 50 stems. There are a lot of rotational partners that can be used for beetle management, including products from 10 different mode of actions. If you used a neonic at planting, do not follow up with a neonic (and it might be best to avoid the Group 4 products entirely, even those in a different subclass like 4D). Likewise if you used Verimark at planting.

Striped cucumber beetles are now active. I am in need of large numbers of beetles from multiple sites. If you have beetles, PLEASE let me know before you kill them so that I might take some beetles out of your field.

Any planted cucurbit needs to be scouted for beetle aggregations. Overwintering adult males release an aggregation pheromone in their feces that acts like a beacon to draw in members of both sex to the field. This behavior contributes to the transmission of bacterial wilt to susceptible cucurbits. Watermelon is not susceptible. Winter squash is susceptible until it has two true leaves, while cucumber and musk melons are very susceptible to wilt. Summer squashes are also susceptible to wilt. Squash seeds treated with Farmore DI-400 should be protected for close to 2 weeks which should be long enough for winter squash to be large enough to withstand the pathogen. For young transplants, the threshold is 2 beetles per plant. If chemigating, be sure to read the labels carefully! There should be charts on the labels designating how much product should be injected per x feet of drip tape. The amount of product that a bed receives is quite a bit more than the amount of product that would fall on the bed if broadcast foliarly. There are also two diamides labeled for cucumber beetles: cyantraniliprole (Exirel) and cyclaniliprole (Harvanta). Diamides do not kill beetles quickly, but beetles do stop feeding very rapidly. If using either product, do not be alarmed if you see live beetles after application. Check for signs of fresh feeding. Later in the season, the easiest way to check for fresh feeding is by examining flowers.

Sweet Corn
Blacklight and pheromone trapping data is uploaded by Tuesday and Friday mornings and can be found here: Many thanks to Richard Monaco and Joseph Deidesheimer for checking traps and uploading data. Threshold information can be found here:

Curiously, the blacklights are currently outperforming the pheromone traps, and in some locations are indicating a spray schedule of about 4 days on silking sweet corn. Trap counts are as follows:

Trap Location BLT – CEW Pheromone CEW
3 nights total catch
Dover 1 0
Harrington 0 0
Milford 0 0
Rising Sun 0 0
Wyoming 2 1
Bridgeville 1 0
Concord 0 2
Georgetown 0 0
Greenwood 0
Laurel 2 0
Seaford 4 0
Trap Pond