PESTS OF CUCURBITS

Pickleworms (on most cucurbits) and squash vine borers (on squash) can cause serious damage to field-grown cucurbits. In the greenhouse, cucumbers are likely to be infested with aphids, spider mites, leafminers, and cucumber beetles, which are common outdoors and in greenhouses, are vectors of the bacterial wilt organism and help spread cucumber mosaic.

KEY TO CUCURBIT PESTS

A. Pests that feed externally on the plant

  1. Chewing insects that leave holes or scars in foliage, fruit, blossoms, and buds

    1. Cabbage looper - Green caterpillar with longitudinal white stripes; body up to 30 mm long, tapers toward head; three pairs of legs near head; three pairs of fleshy prolegs (Fig. 105); young larva on underside of leaf; mature larva seeks protection of large leaves near center of plant; consumes tender leaf tissue leaving most veins

    2. Corn earworm - Moderately hairy caterpillar up to 44 mm long with 3 pairs of legs and 5 pairs of prolegs; early instars: cream colored or yellowish-green with few markings; later instars: green, reddish, or brown with pale longitudinal stripes and scattered block spots (Fig. 106); a late-season pest of flowers and fruits

    3. Cucumber beetles - Oval-oblong beetles 5 to 6 mm long; bright yellowish-green body with 12 black spots on wing covers (Fig. 107A) or pale yellow body with 3 black stripes on wing covers (Fig. 107B); leaves holes in foliage, girdle stems, feed in blossoms, scar fruit

    4. Melonworm - Greenish caterpillar up to 30 mm long; most stages with two white, slender, well-separated stripes down the back; three pairs of legs near the head and 5 pairs of prolegs (Fig. 108); feeds primarily on tender foliage

    5. Pickleworm - Young larva less than 10 mm long, colorless or pale yellow with dark spots; 3 pairs of legs near head and 5 pairs of prolegs (Fig. 109); feeds within blossoms or on small leaves at the growing tips of vines; eventually enters fruit

  2. Pests that cause discoloration or distortion of the upper plant

    1. Greenhouse whitefly - White moth-like insect about 1.5 mm long, found in conjunction with tiny yellow crawlers and/or green oval, flattened, immobile nymphs and pupae (Figs. 110A to F); leaves yellow, some plants stunted and unreproductive; honeydew and black sooty mold may be present on leaves

    2. Melon aphid - Soft-bodies, pear-shaped insect up to 2 mm long with pair of dark cornicles and a cauda protruding from the abdomen (Figs. 111A, B); yellow-bodies in hot, dry summers; pale to dark green-bodied in cool seasons; winged or wingless (wingless form most common); feeds in colonies; causes leaves to curl downward and pucker, wilt, and eventually turn brown; secretes honeydew thereby making plants sticky and promoting the growth of sooty mold

    3. Squash bug nymph and adult - Light gray to dark brown bugs up to 16 mm long (Figs. 112A,B); adult flat across the back and mottled yellow underneath, oval-elongate in shape; congregate on vines; infested vines blacken and wither; fruit sometimes attacked.

    4. Thrips - Foliage-rasping pest; pale yellow to dark brown body 2 mm or less in length; adult with 2 pairs narrow, fringed wings (Fig. 113); causes silvery blotches or scratch-like markings on leaves; some infested leaves distorted, curling upward

    5. Twospotted spider mite - Tiny, almost microscopic, pale to dark green pest with 2 or 4 darkly colored spots; adults and nymphs 8-legged; larvae 6-legged; adult female oval, 0.3 to 0.5 mm long; male more diamond-shaped (Fig. 114); feeds on undersides of leaves; infested foliage with silvery or pale yellow stipples; leaves eventually fade and dry up; silken webs common on undersides of leaves

B. Pests that feed inside leaves, seeds, stems, roots, or fruit

  1. Pickleworm - Yellow-green caterpillar up to 30 mm long with dark head, or smaller pale yellow larva with dark spots; 3 pairs of legs near head and 5 pairs of prolegs (Fig. 115); bore into side of fruits before rind hardens and tunnel inside leaving masses of soft excrement; fruit rots or sours; vines may be riddles with holes

  2. Seedcorn maggot - White to yellow maggot up to 7 mm long; legless body with pointed head (Fig. 116); feeds underground on roots, seeds, and sometimes stems; infested seedlings unthrifty, may yellow, wilt and die

  3. Squash vine borer - Thick-bodied, whitish, wrinkled caterpillar up to 25 mm long with brown head; 3 pairs of legs near head; 5 pairs of prolegs; 2 transverse rows of spines on each proleg (Fig. 117); causes sudden wilting of long runner or entire plant; greenish-yellow excrement protrudes from hole in stem; entrance hole usually near ground; vines become girdled, rot, and die; fruit may be infested

  4. Vegetable leafminer - Colorless to bright yellow maggot up to 3 mm long with pointed head; makes serpentine mine slightly enlarged at one end (Fig. 118)

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