Vegetable Crop Insect Scouting

David Owens, Extension Entomologist,


Snap Beans

Bean leaf beetle are now active in snap beans. They tend to make circular to blocky holes in the leaves. Adults can be white, yellow, red, or orange with or without black spots, but they always have a black triangular spot between the wings. Early thresholds are 1 beetle per plant or 20% defoliation.

Seedcorn maggot injury is also evident in some early planted snap bean fields. Affected plants will have much smaller leaves, ragged discolorations on the cotyledons, or appear as a ‘snake head’ (cotyledons but no or very small leaves growing on the stem instead of normal-looking leaves). Below ground the stem may be swollen or have a discolored shredded appearance. There are no rescue treatments for seedcorn maggot.


Striped cucumber beetle have begun migrating into fields. Early colonizing males release an aggregation pheromone in their feces that attracts females as well as more males. Their feces may also contain the pathogen that causes bacterial wilt. Dew or rain can wash the bacteria into the plant via open wounds. Muskmelons are the most susceptible to bacterial wilt and cucumber beetles should be treated aggressively. Watermelons are not susceptible to bacterial wilt and thus have a much greater tolerance for cucumber beetles. Thresholds for recently transplanted plants are 2 beetles per plant, for older plants the threshold is 5. Be aware however that even if a field is below this threshold, because of the aggregation pheromone there can be intense, if localized, hotspots in the field. In trials last year we observed limited pyrethroid efficacy, but to date have not observed any decrease in neonicotinoid susceptibility. If you decide to treat for cucumber beetles with a drip treatment, pay special attention to the label rates for product per 1000 row ft. Some product labels have this clearly denoted while others might not. Essentially, the rate is per field area, NOT planted or plastic area. Thus, if a bed is 2’ wide, and spaced 7’ apart, the ‘planted area’ is 2’ x row length/43560, but the amount of product to inject in the drip is Rate x 7’ x row length/43560.

Mr. Cody Stubbs scouted several greenhouses this week and found little spider mite activity at most sites, and where he found them, mites were active on weeds and not transplants.

A sample of seedcorn maggot damaged watermelon was submitted earlier this week. There are no rescue treatments for seedcorn maggot. Affected plants will be stunted, have a brown, ragged looking root, and a swollen stem below ground.


Colorado potato beetle has been active for some time now, but now with very warm weather, they will begin flying. If a field is close to last year’s previous field, it will be colonized first. Thresholds are 50 adults, 75 large larvae, or 200 small larvae per 50 stems. There is a wide range of effective, labeled products.

Cole Crops

We looked at a couple of cole crop plantings this week and found signs of imported cabbageworm activity but the only worms detected were diamondback moth. Diamondback moth larvae are small, green to greenish yellow, and wriggle violently when disturbed. They are notorious for developing resistance to commonly used insecticides, thus it is recommended to rotate from one mode of action to another for one month, then rotate among completely different modes of action for the second month before coming back to the first set of MOAs. This needs to be done at the farmscale level. Thresholds are 30% infestation to cupping and then it decreases to 5%. Spreader sticker adjuvants help improve efficacy of most worm products on cole crops, but be mindful not to tank mix a sticker and a translaminar moving product such as a diamide or Radiant. Those products want to move into the leaf tissue while the sticker tries to keep them on the leaf surface.

Solanaceous Fruiting Vegetables

Flea beetles are very active now. If you are seeing a large number of very small holes in leaves, consider treatment with a pyrethroid, neonicotinoid, Torac, or Verimark. Entrust is labeled for flea beetles, as is Botani Gard.