Pests of Crucifers

Crucifers, plants of the mustard family, have a unique set of pests. With the exception of cutworms, the cabbage looper, and the vegetable weevil, these insects pose little or no threat to most other vegetable crops. A group of three caterpillars, known as the "cabbageworm complex," causes most damage to crucifiers. These include the cabbage looper, diamondback moth larva, and the imported cabbageworm. The cabbage maggot is the most important pest of crucifers in western North Carolina.

KEY TO CRUCIFER PESTS

A. Chewing insects that leave holes in foliage or bore into stems and leaf veins

  1. Caterpillars with three pairs of legs and three to five pairs of prologs

    1. Beet armyworm-Soft-bodied green or black caterpillar up to 30 mm long; three lightly colored stripes running length of body; black spot on each side of body on second segment behind head; five pairs of prolegs (Fig. 80); damages bud and young leaves.

    2. Cabbage looper-Green caterpillar with longitudinal white stripes; body up to 30 mm long and tapering toward the head; three pairs of fleshy prolegs (Fig. 81); young larva on underside of leaf; mature larva deep within head; consumes tender leaf tissue leaving most veins intact.

    3. Cabbage webworm-Yellowish gray caterpillar up to 15 mm long; black head with well defined V-shaped mark; mature larva bearing five dark longitudinal stripes and moderately long yellow or light brown hairs; five pairs of prolegs (Fig. 82); bores in plant often destroying bud or causing plant to be deformed; sometimes found in protective web along vein on underside of leaf; usually a problem only in fall.

    4. Corn earworm-Early instars: cream colored or yellowish green with few markings; later instars: green, reddish or brown with pale longitudinal stripes and scattered black spots; moderately hairy; up to 44 mm long; five pairs of prolegs. (Fig. 83)

    5. Cross-striped cabbageworm-Early instars: gray with dark tubercles, large head, and sparse body hairs; mature larva: bluish gray with black transverse stripes and two stripes (one yellow, one black) down each side of the back; larva up to 15 mm long; five pairs of prolegs (Fig. 84); feeds on buds and tender leaves.

    6. Cutworms-Fat, basically gray, brown, or black caterpillars 40 to 50 mm long when fully grown; five pairs of fleshy prolegs (Fig. 85); active at night-young caterpillars climbing on leaves, older caterpillars severing stalks of leaves; hide during the day in soil burrows at base of plants.

    7. Diamondback moth larva-Pale green caterpillar up to 7 mm long with black head and scattered black hairs; five pairs of prolegs; tapers slightly at both ends and wiggles rapidly when disturbed (Fig. 86); prefers to feed on underside of older leaves, between loose leaves, or on young buds; bud damage prevents proper development of heads.

    8. Imported cabbageworm-Velvety green caterpillar up to 32 mm long; yellow stripe down back; row of yellow spots down each side; five pairs of prolegs (Fig. 87); feeds deeper in plant and more likely to eat small veins than the cabbage looper; leaves wet; greenish brown excrement deep among leaves.

  2. Beetles or beetle larvae

    1. Striped flea beetle-Black oval beetle about 2 mm long with a wavy yellow line down each wing cover; enlarged hind legs for jumping (Fig. 88); makes small pits in leaves; remaining tissue drops out leaving small "shot holes"; transmits some plant diseases.

    2. Vegetable weevil adult and larva-Dull grayish brown weevil, about 6.4 mm long, with short, stout snout and light V-shaped mark on wing covers (Fig. 89A); larva pale green, legless, up to 10 mm long with dark mottled head (Fig. 89B); adult and larva feed primarily at night on buds and foliage.

B. Insects with needlelike or rasping mouthparts that cause foliage to be yellowed or distorted

  1. Aphids-Pale green, soft-bodied, pear-shaped insects with a pair of dark cornicles and a cauda protruding from the abdomen; body up to 2.5 mm long; may be winged or wingless-wingless form most common (Fig. 90); feed in colonies; cause discoloration or mottling of foliage; often transmit virus diseases; excrete honeydew on which sooty mold grows.

  2. Harlequin bug-Black, shield-shaped bug up to 10 mm long, brightly colored with orange, red, and yellow markings (Fig. 91); injured stems and leaves with irregular cloudy spots around puncture wound; young plants wilt, brown, die; old plants stunted.

  3. Onion thrips- Foliage-rasping pest; pale yellow to dark brown body 2 mm or less in length; adult with two pairs narrow, fringed wings (Fig. 92); causes silvery blotches or scratchlike markings on leaves; some infested leaves distorted, curling upward.

C. Insects that attack plants below ground.

  1. Cabbage maggot-White legless maggot up to 6 mm long with a pointed head (Fig. 93); occurs only in a few mountain counties of North Carolina; devours small roots; tunnels in stems and fleshy roots making them brown and slimy; above ground, plants stunted and of unusually pale color; infested cabbage has sickly bluish gray leaves.

  2. Cutworms-See A.1.f. for description; soil insects that usually eat foliage; also sever stems near base of plants ..

  3. Vegetable weevil and larva-See A.2.b. for description. Feed at night on foliage or underground on large-rooted crucifers like turnips .
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