Brassicas, or members of the Brassicaceae family, include vegetables like cabbage, brussels sprouts, broccoli and cauliflower. These cole crops are susceptible to a number of pests that cause varying types and levels of damage. Often, these pests can be controlled with the use of proper cultural practices; handpicking; and, if necessary, applications of oils, soaps, pesticides or Bacillus thuringiensis.
Brassica plants may be attacked by a number of aphid species, but the two most prevalent aphid species on these plants are the cabbage aphid and the turnip aphid. These small, whitish-green pests suck sap from plants, causing leaves to curl and crinkle. Heavily-infested plans are dwarfed, wilt or die. Aphids are most problematic during dry, cool weather. If aphids are a problem on only a small scale, spray the plants with soapy water, then rinse with clear water. To deal with a larger infestation, repeat applications of an insecticide may be necessary.
The cabbage maggot (Delia radicum) is the legless, white larva of a fly that resembles the common housefly. Larvae eat fibrous roots and burrow into the roots, causing plants to suddenly wilt and die. Affected roots will have brown grooves and slimy channels. The flies are attracted to areas with large amounts of decaying matter, so reducing the amount of matter decomposing in a garden will limit this pest. Avoid this pest by tilling the ground at least four weeks prior to planting and limiting post-emergent herbicide use.
The harlequin bug, known scientifically as Murgantia histrionica, is a red and black-spotted, shield-shaped bug that sucks fluids from plants, causing them to wilt, brown and die. While young plants are most vulnerable, larger plants will suffer from yellowing and slowed growth. If necessary, harlequin bugs can be treated with herbicides that contain the active ingredients permethrin, bifenthrin or cyfluthrin.
Flea beetles are tiny, blue-black insects that chew holes in leaves. Well-established plants can withstand a fair amount of flea beetle damage, so control actions may not be warranted. If necessary, floating row covers can be used to protect crops or flea beetles can be treated using a number of insecticides.
The larvae, or caterpillars, of several butterflies or moths can be destructive pests on brassica plants. The cabbage lopper (Trichoplusia ni) begins as a caterpillar with a translucent body and dark head before maturing into a pale green, 1 1/2-inch-long larva that moves like an inchworm. This pest can be quite destructive, eating leaves and moving inward toward the center of the plant. The cabbage webworm (Hellula rogatalis) is a dull grayish-yellow with five brown stripes and a black head. This caterpillar forms a protective web under which it feeds, tunneling into and killing the buds of young plants, causing the plant to produce secondary buds. The cross-striped cabbageworm (Evergestis rimosalis) is gray or blueish-gray with black and yellow horizontal stripes. This pest eats holes in the terminal buds and heads of cole crops. The important cabbageworm (Pieris rapae) is velvety green with narrow orange and yellow stripes. Damage caused by the imported cabbageworm resembles damage caused by the cabbage lopper. The diamondback moth caterpillar (Plutella xylostella) is light green and has pointed ends. This caterpillar wriggles when disturbed and will feed on any plant part but prefers the area around the buds of young plants. Caterpillars are most thoroughly addressed using a combination of hand-picking and applications of Bacillus thuringiensis.
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