David Owens, Extension Entomologist, owensd@udel.edu
Cucurbits
Striped cucumber beetle aggregations have been observed this week in cantaloupe and squash. Begin scouting all watermelon transplants! This includes plants on the transplant wagons, recently transplanted, and any cucurbit in the ground besides watermelon. Thresholds in watermelons are 2 beetles per plant. The most effective insecticides early-season and pre-bloom are neonicotinoids injected through the drip, provided it is done correctly. Pay attention to label guidelines on how much insecticide should be used per 1,000 row feet of drip tape and your given row spacing. Note that the amount changes depending on how far apart the beds are (5 ft centers use less insecticide per 1,000 feet of drip than 7 ft centers, but there is more drip tape). It may seem to make sense to only use the amount covered by plastic as the treated area, but this will result in a serious under-treatment! Cucurbits transplanted early may be in bloom already. In such cases, consider using Assail over a foliar thiamethoxam or imidacloprid. A couple of diamides are labeled for striped cucumber beetle but are best used later in the season when rind worms are also a problem. Assail will not impact the worm complex, and the diamides are superb worm insecticides.
Potato and Eggplant
Colorado potato beetles continue to migrate into fields. Potato thresholds are 50 beetles per 50 stems and up to 200 small larvae per 50 stems (or 15-20% defoliation). Eggplant defoliation thresholds are lower, at 10%. If a neonicotinoid was used in furrow, switch modes of action. The diamides give excellent CPB control, as do other products typically used against other pests such as Radiant (often for worms), Agri-Mek (typically a miticide), and Torac. Later in the season, Agri-Mek has the added benefit of being an excellent miticide. Eggplants are quite susceptible to mite injury.
Mites
In diverse farm scapes, mites may be harbored in early season vegetables. This week we visited strawberry fields scouting for mites, cyclamen mite, and tarnished plant bug. If you have experienced cyclamen mite damage, please let us know!!! We are trying to get a better understanding of the impact this critter has on strawberry production. In a couple of locations, summer vegetables were transplanted within fairly close proximity to strawberries. Scout these plants carefully for mites. Strawberry can harbor large populations of mites before plant health is significantly impacted, but that is not true of tomatoes, eggplants, and some cucurbits.
Beans
We are starting to see seedcorn maggot damage in our legume trials on station. While warm, dry weather is not as conducive to SCM, it only takes a couple of days of the wrong conditions in a highly attractive field to result in significant injury. Still consider using an insecticidal seed treatment. Plants that have been impacted by SCM will be stunted, the stems below ground will be swollen, or you may see a ‘snake head’ plant where the cotyledons emerge but the growing point has been damaged/died above the cotyledons. Begin scouting for bean leaf beetle. It should be making an appearance soon.