Vegetable Crop Insect Scouting

David Owens, Extension Entomologist, owensd@udel.edu

Cucurbits
Continue scouting for all three major melon pests: cucumber beetles, rind-feeding Lep pests of various species, and spider mites. The general threshold for cucumber beetles is 2 per plant, but you may want to consider being a little more aggressive on treating them in cantaloupe. Cantaloupe rinds are soft enough the beetles can gouge and pit them, whereas in watermelon their feeding is more superficial. Acetamiprid is the best material for cucumber beetles. Do not rely on pyrethroids in our area. If worms are a concern, Harvanta has fairly good cucumber beetle efficacy and is excellent on worms. Recent wet weather is not enough to dislodge mites, continue scouting for them. Magnification is a major help because it will help you determine whether the mites are live or dead.

Squash bugs are the major threat right now to summer squash. PLEASE NOTE: Carbaryl is labeled for squash bug control but gives only fair control at best. Instead, consider using a pyrethroid or Assail. Assail is best on small nymphs and eggs (no, it wont kill eggs, but it has a long enough residual it should kill hatching nymphs).

If your plants have squash vine borer in them, it is too late to kill larvae. We just evaluated a zucchini trial this week, zucchini plants were planted at the end of May and weekly treatments applied beginning mid-June upon vine borer emergence. A weekly pyrethroid application completely prevented vine borer damage. Please note that we do have a second flight period of vine borer in August.

Potatoes, Peppers, Eggplants, and Tomatoes
Continue scouting for stink bug damage to fruit. Stink bugs are best managed with bifenthrin containing products or (where labeled) dinotefuran. Of the neonicotinoids, dinotefuran exhibits very good stink bug efficacy whereas the others are fair.

Beet armyworm is active, we have a handful of beet armyworm traps out and our western Laurel traps appear to be catching quite a few more than other sites in Sussex County. I do not have any traps in northern or eastern Sussex. Scout peppers for webbing and window paning indicative of early instars recently hatched from egg masses.

Colorado potato beetle adults are active and laying. Scout eggplants and potato for both them and for spider mites; eggplant is a spider mite magnet. Agri-mek should provide good Colorado potato beetle control and excellent mite control. There are numerous materials that are excellent for potato beetles or spider mites, but abamectin is the only one good for both.

Please note that while bifenthrin does have some mite activity, it is short lived and often leads to a resurgence in mite numbers. If a pyrethroid is used for leafhopper, it has a good fit, but should not be used alone for mites. Potato leafhoppers are becoming more numerous in the landscape. Scout potatoes, especially if near an alfalfa field.

Lima Beans
Lima beans are beginning to flower, now is the time to scout for tarnished plant bug and begin scouting for stink bugs. In dry corners of fields, also scout for spider mites. If you have mites, please let me know, we need pictures!

Tarnished plant bugs are often especially numerous in areas with heavy pigweed populations. Thresholds are 15 per 50 sweeps; labeled materials include Lannate, Orthene (but not for long!), dimethoate, pyrethroids, transform and Beleaf. Of those materials, Beleaf has the narrowest spectrum, but is excellent on them and aphids. Interestingly, it is not effective on stink bugs.

Sweet Corn
Scout whorl stage sweet corn NOW for fall armyworm. The threshold in mid to late whorl stage is 30%, but once the tassel is emerging, the threshold goes down to 15%. As much as possible use high volume sprays directed into the whorl. While chlorantraniliprole is our best material for FAW, we are limited in how much we can use; I would prefer to save all that active ingredient for corn earworm silk sprays. Avaunt, Radiant, and Intrepid Edge should all provide good control.

Corn earworm activity is unusually high for this time of year. This may be because both the hot weather and delayed corn planting. Pay attention not just to pheromone counts but also blacklight trap counts. Blacklight trap counts of 2 or more below indicate a 3 day spray schedule (https://www.udel.edu/academics/colleges/canr/cooperative-extension/sustainable-production/pest-management/insect-trapping/silk-stage-sweet-corn/). Next week there are chances of thunderstorms. If a rain event occurs shortly after a pyrethroid application, expect to lose some efficacy and retreat sooner. I do not think the decrease in efficacy is quite as pronounced following a Besiege or Elevest treatment, but we will be testing this question later in the season. Begin earworm sprays at first silk; if fall armyworm is not present in the tassels, there is little benefit to starting before first silks are out. Keep a tight spray schedule for the first 10 days of the silking period.

Thursday trap counts are as follows: