David Owens, Extension Entomologist, owensd@udel.edu
Cucurbits
Continue scouting for striped cucumber beetle in young transplants. If a field has been treated with a neonicotinoid, you may see both dead and live beetles. Live beetles may have recently migrated into the field and have not fed on enough plant material to receive a fully toxic dose. It sometimes takes a day or two to kill beetles after an application. Other beetles will stop movement but stay on the plants, almost as if frozen in place.
Snap Bean
Scout for thrips and for leafhopper in young snap bean plants and take note of any bean leaf beetle damage observed (circular to rectangular holes in leaves). On seedling snaps, thrips thresholds are 5-6 per leaflet and 5 leafhopper per sweep; this rises as the plants get closer to flowering.
Potatoes
Scout now for Colorado potato beetle and for leafhopper. CPB thresholds are 50 adults per 50 stems or 200 small larvae per 50 stems. While looking at stems, look under leaves to see if you can spot leafhopper. The threshold for the small potato leafhopper is 1 per 10 sweeps. At-plant neonics should still have enough residual to work, but it is getting weak at this point.
Sweet Corn
Early season pests of sweet corn planted into cover crop, particularly a small grain type cover, include stink bug and cutworm. Stink bugs can kill the growing point causing the plant to tiller excessively. Signs of stink bug feeding include jagged holes in rows or long slit like holes, and yellow edges around the hole. While thresholds specific to brown stink bugs in sweet corn have not been worked out, in grain corn it is 13 bugs per 100 plants. Cutworm thresholds in field corn are between 3 and 5% plants or 10% with early stage cutworm leaf feeding (circular holes in rows) and cutworm is still present. I imagine for sweet corn, somewhat lower thresholds are justifiable, particularly in fresh market non-processing fields.