Key to Cucurbit Pests
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.
A. Pests that feed externally on the plant
- Chewing insects that leave holes or scars in foliage, fruit, blossoms, and buds
- 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 (Figure 1); young larva on underside of leaf; mature larva seeks protection of large leaves near center of plant; consumes tender leaf tissue leaving most veins
- Corn earworm – Moderately hairy caterpillar up to 44 mm long with 3 pairs of legs and 5 pairs of prolegs (Figure Z); early instars: cream colored or yellowish-green with few markings; later instars: green, reddish, or brown with pale longitudinal stripes and scattered block spots (Figure 2); a late-season pest of flowers and fruits
- Cucumber beetles – Oval-oblong beetles 5 to 6 mm long; bright yellowish-green body with 12 black spots on wing covers (Figure 3A) or pale yellow body with 3 black stripes on wing covers (Figure 3B); leaves holes in foliage, girdle stems, feed in blossoms, scar fruit
- 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 (Figure 4); feeds primarily on tender foliage
- 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 (Figure 5); feeds within blossoms or on small leaves at the growing tips of vines; eventually enters fruit
- Pests that cause discoloration or distortion of the upper plant
- 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 (Figure 6A-F); leaves yellow, some plants stunted and unreproductive; honeydew and black sooty mold may be present on leave
- Melon aphid – Soft-bodies, pear-shaped insect up to 2 mm long with pair of dark cornicles and a cauda protruding from the abdomen (Figure 7A-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
- Squash bug nymph and adult – Light gray to dark brown bugs up to 16 mm long (Figure 8A-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.
- Thrips – Foliage-rasping pest; pale yellow to dark brown body 2 mm or less in length; adult with 2 pairs narrow, fringed wings (Figure 9); causes silvery blotches or scratch-like markings on leaves; some infested leaves distorted, curling upward
- 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 (Figure 10); 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
- 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 (Figure 11); 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
- Seedcorn maggot – White to yellow maggot up to 7 mm long; legless body with pointed head (Figure 12); feeds underground on roots, seeds, and sometimes stems; infested seedlings unthrifty, may yellow, wilt and die
- 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 (Figure 13); 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 (Figure X)
- Vegetable leafminer – Colorless to bright yellow maggot up to 3 mm long with pointed head; makes serpentine mine slightly enlarged at one end (Figure 14)
Spotted cucumber beetle, Diabrotica undecimpunctata howardi Barber, Chrysomelidae, COLEOPTERA
Striped cucumber beetle, Acalymma vittata (Fabricius), Chrysomelidae, COLEOPTERA
Adult – Cucumber beetles are oblong-oval in shape and have beaded antennae about 2 mm long. Six mm long, the spotted cucumber beetle has a bright yellowish-green body with black head, legs, and antennae. Wings are marked with 12 black spots. Five mm long, the striped cucumber beetle is pale yellow with a black head and 3 black stripes down its back.
Egg – The oval orange-yellow eggs are found in clusters of 25 to 50 on undersides of host leaves. Each egg is about 0.6 mm long and 0.4 mm wide.
Larva – Cucumber beetle larvae have a yellow-white, somewhat wrinkled body with 3 pairs of brownish legs near the head and a single pair of prolegs near the tip of the abdomen. When fully grown, spotted cucumber beetle larvae are 13 to 19 mm long; striped cucumber beetle larvae are only 10 mm long and have a more flattened abdomen.
Pupa – Pupae are white, tinged with yellow and 6 to 8 mm long. A pair of black spines is located at the tip of the abdomen.
Distribution – These native insects occur from Mexico to Canada. They are most abundant and destructive in their southern range, but usually are not troublesome in areas with sandy soils.
Host Plants – Cucumber, cantaloupes, winter squash, pumpkin, gourd, summer squash and watermelon are preferred by adult striped cucumber beetles. They also feed on bean, pea, corn, and the blossoms of several wild and cultivated plants. Larvae develop on these and related cucurbits. The spotted cucumber beetle has a wider host range and, in addition to cucurbits, may be found on bean, pea, potato, beet, tomato, eggplant, and cabbage. The larva is the well known southern corn rootworm which feeds on the roots of corn, peanuts, small grains, and many wild grasses.
Damage – Striped and spotted cucumber beetle adults feed on the foliage and stems of cucurbits all season long. They often girdle stems by gnawing on the tender shoots of seedlings. As plants develop, beetles also feed on blossoms and leave scars on the fruit. Adult cucumber beetles harbor bacterial wilt organism (Pseudomonas lachrymans) in winter and transmit it during the growing season. They also help spread squash mosaic virus. Larvae injure plants by feeding on roots and tunneling through stems.
Life History – Unmated adults overwinter in neighboring woodlands under leaves and trash or around the bases of plants that have not been killed by frost. Adults leave their winter sites in late March. Before cucurbits are available, the beetles subsist on the pollen and petals of many plants. As soon as cucumber, squash, or melon vines appear, beetles devour cotyledons and stems. Females of the overwintering generation lay eggs from late April through early June, each female depositing as many as 500 eggs. Depending on temperature, eggs incubate for 7 to 10 days before hatching. Larvae feed in the soil on stems and roots for 2 to 4 weeks before pupating. First generation adults emerge from late June to early July. Over the next 6 to 9 weeks, the life cycle is repeated, second generation adults being prevalent from September to November. These later adults assemble on clover and alfalfa upon which they feed until winter. They may come out to feed during warm periods in January and February. Two generations and sometimes a partial third are produced each year.
Several cultural measures discourage cucumber beetles. First, early plowing-discing removes vegetation and discourages egg-laying. Delayed planting (more favorable germinating conditions) and heavy seeding rates ensure a good stand. Wire or cloth screen protectors shaped like cones will keep beetles off home plantings until plants get established.
The use of resistant varieties is perhaps the most important control tactic. The following cucurbit varieties are resistant to spotted cucumber beetles as seedlings and also have resistant foliage later in the season: Blue Hubbard (squash); Ashley, Chipper, Gemini (cucumber). The North Carolina Extension publication AG-25, Control Vegetable Insects Using Cultural Methods, gives a more thorough and extensive listing of resistant varieties. Use of resistant varieties may not give complete control where infestations are heavy.
A foliar insecticide applied at the cotyledon stage will retard cucumber beetle feeding and encourage plant establishment. Where insects are abundant, additional foliar applications may be needed to prevent beetles from spreading bacterial wilt and squash virus. For recommended insecticides and rates, consult the current North Carolina Agricultural Chemicals Manual.
Garden fleahopper, Halticus bractatus (Say), Miridae, HEMIPTERA
Adult – There are three forms of garden fleahopper adults: slender long-winged females; oval-bodied short-winged females; and slender long-winged males. All forms are black and have long legs and antennae. They tend to jump actively but are also capable of flying. The body may be 1.6 to 2.0 mm long.
Egg – Each white, somewhat curved egg is rounded at one end, truncate at the other, about 7 mm long and 1 to 2 mm wide. Usually inserted into the plant, the egg is seldom ever seen.
Nymph – Nymphs are pale yellow to dark green and range from 0.7 to 2 mm in length with 5 instars. Later instars have a distinct black spot on each side of the first thoracic segment. All stages have a jumping habit.
Distribution – Though infestations are sporadic in occurrence, garden fleahoppers can be found throughout the eastern United States as well as in some western areas.
Host Plants – A wide range of garden, ornamental and forage plants as well as many weeds and grasses are subject to infestation by this fleahopper. Vegetable hosts include bean, beet, cabbage, celery, corn, cowpea, cucumber, eggplant, lettuce, pea, pepper, potato, pumpkin, squash, sweet potato, and tomato.
Damage – Garden fleahoppers cause pale spots to develop on leaves by sucking sap from the foliage. Heavily infested foliage dies and drops from the plant. Defoliation naturally interferes with growth and development of crop causing yield reduction.
Life History – Garden fleahoppers overwinter as eggs laid from August through September. Nymphs emerge in early spring and feed on undersides of leaves. Nymphs feed and develop from 11 to 35 days before maturing into adults, the duration depending on temperature.
Adults live 1 to 3 months. Each female lays approximately 105 eggs. Eggs are inserted into punctures made by the mouthparts in stems or leaves. About 12 to 20 days later, eggs hatch and the life cycle is repeated. Five generations are completed each year.
For up-to-date chemical recommendations, consult the current North Carolina Agricultural Chemicals Manual.
Melon aphid, Aphis gossypii Glover, Aphididae, HEMIPTERA
Adult – This soft-bodied, pear-shaped insect is pale to dark green in cool seasons and yellow in hot, dry summers. Though winged forms develop periodically, most adults are wingless and about 2 mm long. All forms have a pair of tailpipe-like appendages known as cornicles.
Egg – The egg stage does not occur in North Carolina.
Nymph – The nymph is smaller than but similar in shape and color to the wingless adult.
Distribution – The melon aphid is distributed throughout the temperate, subtropic, and tropic zones of the world. It occurs in all areas of North Carolina.
Host Plants – A wide range of field and ornamental as well as vegetable crops may be infested by this pest. Some vegetable hosts include asparagus, bean, beet, cowpea, cucurbits, eggplant, okra, spinach, and tomato. Among cucurbits, cucumber and melon are most likely to be infested, followed by squash and pumpkin.
Damage – Damage usually becomes obvious on cucurbits after the vines begin to run. If weather is cool during spring, populations of natural enemies will be slow in building and heavy aphid infestations may result. Congregating on lower leaf surfaces and terminal buds, aphids pierce plants with their needle-like mouthparts and extract sap. When this occurs, leaves curl downward and pucker. Wilting and discoloration follow. Aphid damage weakens plants and may reduce fruit quality and quantity. Honeydew secreted by aphids makes plants sticky and enhances development of black sooty mold on plant foliage.
Life History – In North Carolina, melon aphids spend part of the winter on weed hosts and in gardens on cold tolerant plants such as spinach. During warm periods, they continue feeding until cold weather inactivates them. In spring, winged females fly to suitable host plants and give birth to living young. Each female produces an average of 84 nymphs. Under favorable conditions, a nymph will mature in about 5 days and begin producing its own progeny. Most nymphs develop into wingless adults. However, when crowding occurs or food becomes scarce, winged adults develop and fly to new host plants. Reproduction continues through the winter as in the summer but at a much slower rate. Many overlapping generations are produced each year.
Predators such as lady beetles and their larvae, syrphid fly larvae, and aphid lion larvae reduce melon aphid populations. A small parasitic wasp is also an important natural control agent. In addition, damp weather promotes a fungus disease and hard, driving rains tend to kill large numbers of aphids.
Aphids can be controlled by cultural practices that keep insects in check and by insecticide applications. Planting in a well-prepared, fertile seedbed helps produce a vigorous crop better able to withstand aphid attack. Such a seedbed should not be located near an aphid-infested crop or on land from which an aphid-infested crop has recently been removed.
Insecticides should be applied when it becomes evident that natural and cultural controls are not keeping aphids in check. For up-to-date recommendations and rates, consult the current North Carolina Agricultural Chemicals Manual.
Pickleworm and Melonworm
Pickleworm, Diaphania nitidalis (Stoll), Pyralidae, LEPIDOPTERA
Melonworm, Diaphania hyalinata (Linnaeus), Pyralidae, LEPIDOPTERA
Adult – The pickleworm moth has a large, pale yellow spot near the center of each dark brown forewing; the pale yellow hind wings have a wide, dark brown border. Wingspan is about 32 mm. A cluster of dark brush-like hairs is present on the tip of the abdomen.
The melonworm moth has a brown head and a white-tipped abdomen with bushy hair-like scales. Its white wings have a narrow dark band around the margin and span up to 43 mm.
Egg – Deposited singly or in small clusters on the foliage, the white eggs gradually turn dull yellow before hatching. Variable in shape, each egg is about 0.5 mm in diameter.
Larva - About 1.5 mm long, the newly hatched pickleworm larva is almost colorless except for slightly darker jaws and a black spot on each side of the head (Figure T). Third and fourth instar larvae are about 6 to 12 mm long and pale yellow with dark spots, each spot containing a large bristle. The dark-headed fifth instar larva has a yellow-green body with no spots and may be 25 to 30 mm long (Figure U).
The slender, greenish melonworm larva has two thin white stripes down its back in all but its first and last instars. It is 25 to 30 mm long when fully grown.
Pupa – Enclosed in a thin silken cocoon, the white pupa turns reddish-brown soon after forming. Pupae are about 16 mm long.
Distribution – The pickleworm has been reported from Canada southward into South America. In this country it is a year-round inhabitant of southern Florida. Each summer the moth migrates into North Carolina, further northward into Iowa and Connecticut, and westward to Oklahoma and Nebraska. The melonworm, however, is rarely found north of the Gulf states.
Host Plants – These two caterpillars infest only cucurbits. Though the pickleworm prefers summer squash, it may severely damage cucumber and cantaloupe also. Watermelon, muskmelon, winter squash, pumpkin, and gourd are rarely damaged by this pest. The melonworm prefers foliage of muskmelon, squash, cucumber, and pumpkin. It very rarely attacks watermelon.
Damage – Unlike the melonworm which is primarily a foliage feeder, the pickleworm causes important economic damage to fruit. Young pickleworms usually feed for a time among small leaves at the growing tips of vines or within blossoms. A favorite place is the large staminate flower of squash where larvae hide under the ring of stamens at the base of flowers.
When about half grown, pickleworms normally bore into sides of fruits and continue to feed there causing internal damage and producing soft excrement (Figure V). Both young and old fruits are attacked, but they prefer young fruits before the rind has hardened. Pickleworms make holes in the rind. After the rind has been punctured, the fruit soon rots, or, in the case of cantaloupes, becomes "sour." As the infestation increases, young fruits and flowers are damaged. Growing vines sometimes become riddles with holes and cease to grow.
Life History – Pickleworm moths migrate northward from Florida in the spring. They usually appear in the Raleigh area by early July. Eggs are deposited singly or in small clusters on hairy surfaces of plants. Approximately three days later young pickleworms emerge. After feeding for two weeks ore more larvae spin thin cocoons within rolled leaves and pupate. Five to seven days later, a new generation of moths emerges. In North Carolina, pickleworms complete two full generations and a partial third, if food is available and there is no early frost. The life cycle of melonworms is similar.
In North Carolina, field experiments have shown distinct differences in susceptibility or resistance of cucurbit varieties to pickleworms. The more resistant squash varieties are Butternut 28, Buttercup, Boston Marrow, Blue Hubbard, and Green Hubbard. Gemini cucumbers, Edisto 47 and Honeydew cantaloupes, Blue Ribbon and Crimson Sweet watermelons, and Green Striped Cushaw, King of the Mammoth, and Mammoth Chili pumpkins also show good resistance to pickleworms. Tests with insecticides show much better control of pickleworms on resistant varieties than on susceptible varieties.
Insecticide applications should begin immediately when pickleworms or their damage appear. A few plants of a susceptible squash variety would help detect the first appearance of pickleworms, especially by the presence of insects in flowers. Make applications at weekly intervals after picking fruit and never just before. Apply in later afternoon to minimize bee kills. For recommended insecticides and rates, consult the current North Carolina Agricultural Chemicals Manual.
Squash bug, Anasa tristis (DeGeer), Coreidae, HEMIPTERA
Adult – This hard, oval-elongate bug is dark brown, mottled with light gray on its back side and mottled yellow on its underside (Figure W). About 16 mm long, it is flat across its back and gives off a disagreeable odor when crushed. Typical of all true bugs, the mouthparts are needle-like.
Egg – Roughly diamond- or spindle-shaped, each egg is white when first deposited but gradually turns yellowish-brown and finally dark bronze. It is approximately 1.5 mm long and 1 mm wide. Arranged in a checker-like pattern, eggs typically occur on the foliage in masses of 20 to 40.
Nymph – The five nymphal instars range in length from 2.5 to 10 mm. The first instar is green with rose-colored legs, antennae, and head. These appendages darken in a few hours. Subsequent instars are grayish-white with dark heads, legs, and antennae. The last two instars have noticeable wing pads.
Distribution – Squash bugs occur from Canada into Central America and can be found throughout the United States. Within vegetable gardens, they usually hide under leaves or around the base of plants. These bugs characteristically shy away or move to cover when approached.
Host Plants – All cucurbit vine crops are subject to squash bug infection. The bugs prefer squash, pumpkin, cucumber, and melon, in that order. Hubbard, winter, and marrow squash are often heavily infested.
Damage – Feeding in colonies, adults and nymphs pierce vines with their needle-like mouthparts. While feeding, they inject a toxic substance into plants. As a result, vines quickly turn black and dry out. This aspect of squash bug damage superficially resembles bacterial wilt symptoms. Small plants and individual runners of large vines are often destroyed. When infestations are heavy, fruit may not form. If fruit does develop, bugs may congregate and feed on unripe fruit itself.
Life History – Squash bugs overwinter as unmated adults under plant debris or other suitable shelter. When cucurbit vines start to run in spring, squash bugs fly into gardens and mate. Over a period of several weeks, eggs are laid on undersides of leaves, typically in the angles formed by leaf veins. One or two weeks later, depending on the temperature, nymphs hatch from the eggs and begin to feed. Four to 6 weeks pass before nymphs develop into adults. Because of the prolonged egg-laying period, nymphs and adults are present throughout summer. Feeding continues until frost forces adults into hibernation. One generation occurs each year.
Good cultural practices help prevent serious squash bug damage. Proper fertilization of vines produce a vigorous crop better able to withstand insect attack. The planting of resistant squash varieties such as Butternut, Royal Acorn and Sweet Cheese also reduces squash bug problems. Removal and destruction of crop debris after harvest eliminates some potential overwintering sites for squash bugs.
In small gardens, adult squash bugs and leaves with egg masses can be handpicked and destroyed. The bugs can also be trapped by placing small boards near the host vines. Squash bugs gather under the boards at night and are easily collected and destroyed the next morning.
Should a significant infestation develop, insecticide recommendations and rates can be found in the current North Carolina Agricultural Chemicals Manual.
Publication date: Feb. 10, 2003
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