Master Gardener: Insects eating your broccoli and cauliflower

All of the cole crops, including broccoli and cauliflower, are subject to attack by several kinds of insects throughout the growing season. The following insects cause losses in broccoli, cabbage and cauliflower via damage to the plant by reducing yield, lowering quality, or contaminating the product:

Cabbage looper

Imported cabbageworm

Diamondback moth

Cutworms (climbing and non-climbing)

Zebra caterpillar

Thrips

Cabbage aphid

Green peach aphid

Turnip aphid

Cabbage maggot

Flea beetle

Because insecticides are available in a variety of concentrations, read the label for insecticide application rates and all safety instructions for you and the food you plan to eat.

As a general rule, a treatment for cabbage maggot control is advisable at planting time. During the larval stage, this insect feeds on the plant roots and, when abundant, causes plants to grow slowly and produce poor quality heads. Plants may be killed during serious infestations. Cabbage maggot damage is most common on soils that are high in fresh organic matter. Infestations intensify during extended periods of cool, wet weather. Recommended insecticides include diazinon, either as a furrow drench or in the transplant water, and chlorpyrifos incorporated into the soil around the plant roots.

Cutworms, flea beetles and aphids tend to be most damaging to young plants. Cutworm feeding results in plants that are cut off at or just below the soil surface. Often this type of feeding is preceded by some leaf chewing. If you notice cut plants or leaf feeding, check under dirt clods and crop debris to confirm that cutworms are present. Note that most of the feeding occurs at night, and larvae hide near the base of the plants during the day. Use carbaryl (Sevin) or trichlorofon (Dylox).

Flea beetle injury is characterized by a “shot hole” type of feeding wound. Infestations often are restricted to spot locations. Seeding plants are particularly susceptible to this injury; insecticide treatment occasionally is warranted. Carbaryl (Sevin), endosulfan (Thiodan),or diazinon are recommended spray treatments. One of the registered pyrethroids will also work well. Beyond the seedling stage, only extremely severe infestations will cause yield reductions in production.

Several species of aphid (e.g., cabbage aphid, turnip aphid and green peach aphid) commonly are found on broccoli and cauliflower. When abundant on new growth, they can cause curling and other deformations of the expanding leaves. Infestations of aphids often are associated with extended periods of cool weather, or they may be induced by repeated applications of insecticides that destroy natural aphid enemies. Aphid injury to mature plants is rare. Recommended aphid control treatments include diazinon, malathion, or mevinphos (Phosdrin). Thorough coverage of the plants is necessary.

Several species of caterpillars can be found feeding on the foliage of broccoli and cauliflower. Usually imported cabbageworm, which is the larval stage of the familiar cabbage butterfly, is the most abundant species. Mid- to late-season, cabbage looper may be important. Zebra caterpillar and the smaller larvae of the diamondback moth and webworms also may be present. Established plants (beyond the four-five true leaf stage) can tolerate 50-percent defoliation until the pre-heading stage without yield loss. If serious infestations threaten, recommended treatments are: azinphosmethyl (Guthion), Bacillus thuringiensis formulations are labeled, carbaryl (Sevin), or permethrin. When cabbage looper is present in large numbers, permethrin or spinosad can be used.

As heading of plants begins, these insects become more important as potential contaminants of vegetables. Caterpillars are particularly common in broccoli heads. Two insecticide applications spaced four to seven days apart prior to harvest are suggested to eliminate or minimize insect contaminants. In cauliflower, insect contaminants are less frequent, but insect excrement may fall on the head from larvae feeding on the wrapper leaves. A spray application made immediately prior to blanching and again seven to ten days prior to harvest should eliminate this problem.

Resource: University of Minnesota Extension

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