Key to Crucifer Pests
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.
A. Chewing insects that leave holes in foliage or bore into stems and leaf veins
- Caterpillars with three pairs of legs and three to five pairs of prolegs
- 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 (Figure 1); damages bud and young leaves.
- Cabbage looper – Green caterpillar with longitudinal white stripes; body up to 30 mm long and tapering toward the head; three pairs of fleshy prolegs (Figure 2); young larva on underside of leaf; mature larva deep within head; consumes tender leaf tissue leaving most veins intact.
- 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 (Figure 3); 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.
- 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. (Figure 4)
- 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 (Figure 5); feeds on buds and tender leaves.
- Cutworms – Fat, basically gray, brown, or black caterpillars 40 to 50 mm long when fully grown; five pairs of fleshy prolegs (Figure 6); 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.
- 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 (Figure 7); prefers to feed on underside of older leaves, between loose leaves, or on young buds; bud damage prevents proper development of heads.
- 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 (Figure 8); feeds deeper in plant and more likely to eat small veins than the cabbage looper; leaves wet; greenish brown excrement deep among leaves.
Beetles or beetle larvae
- Striped flea beetle – Black oval beetle about 2 mm long with a wavy yellow line down each wing cover; enlarged hind legs for jumping (Figure 9); makes small pits in leaves; remaining tissue drops out leaving small "shot holes"; transmits some plant diseases.
- 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 (Figure 10A); larva pale green, legless, up to 10 mm long with dark mottled head (Figure 10B); 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
- 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 (Figure 11); feed in colonies; cause discoloration or mottling of foliage; often transmit virus diseases; excrete honeydew on which sooty mold grows.
- Harlequin bug – Black, shield-shaped bug up to 10 mm long, brightly colored with orange, red, and yellow markings (Figure 12); injured stems and leaves with irregular cloudy spots around puncture wound; young plants wilt, brown, die; old plants stunted.
- Onion thrips – Foliage-rasping pest; pale yellow to dark brown body 2 mm or less in length; adult with two pairs narrow, fringed wings (Figure 13); causes silvery blotches or scratchlike markings on leaves; some infested leaves distorted, curling upward.
C. Insects that attack plants below ground
- Cabbage maggot – White legless maggot up to 6 mm long with a pointed head (Figure 14); 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.
- Cutworms – (See above for description). Soil insects that usually eat foliage; also sever stems near base of plants.
- Vegetable weevil and larva – (See above for description). Feed at night on foliage or underground on large-rooted crucifers like turnips.
Cabbage and Turnip Aphids
Adult – Very similar in appearance, these two aphid species are pale green and, most commonly, wingless (Figure M). Both species have a pair of short swollen cornicles (tailpipe-like appendages) on their abdomens. The cornicles of the cabbage aphid are shorter than the turnip aphids. The cabbage aphid is 2.0 to 2.5 mm long and covered with grayish waxy coat. The turnip aphid has no such covering and is 1.6 to 2.2 mm long.
Egg – Virtually nonexistent in the south, the eggs of these aphids are minute, ovate, and black and are laid only in the fall.
Nymph – The wingless nymphs resemble the adults in color and shape but are smaller.
Distribution – Widely distributed throughout the United States, cabbage and turnip aphids are most troublesome in the southern states.
Host Plants – The cabbage aphid feeds primarily on broccoli, Brussels sprout, cabbage, cauliflower, collards, kale, and radish. Mustard is rarely infested. The turnip aphid typically infests mustard, radish, shepherdspurse, turnip, and watercress. It also injures other crucifers, particularly in their seedling stage.
Damage – Aphids cluster on the underside of leaves and suck sap causing infested foliage to curl, wilt, or become distorted. Some infested plants are soon killed; others grow slowly, are stunted, and produce small unmarketable heads.
Life History – In North Carolina, cabbage and turnip aphids continue to feed and breed at reduced rates throughout the winter. Collards are an important overwintering host plant. As warm weather returns, aphid activity increases. Wingless female adults produce large numbers of live progeny (50 to 100) without mating, which all develop into females. Periodically, winged females develop and fly to new host plants. Favored by moderate temperatures and dry weather, reproduction continues in this manner throughout summer. As many as 30 to 45 annual generations occur along the Gulf Coast though not quite so many are produced in North Carolina.
Cultural practices are helpful in avoiding aphid infestations. Plant the crop in a well-prepared, fertile seedbed to promote vigorous growth. Avoid planting near an aphid-infested crop or on land from which such a crop has been recently removed.
Chemical control of aphid infestations is often necessary. For up-to-date recommendations, consult the current North Carolina Agricultural Chemicals Manual.
Cabbage looper, Trichoplusia ni (Hubner), Noctuidae, LEPIDOPTERA
Adult – The cabbage looper moth has a wingspan of about 38 mm. Near the center of each brownish-gray forewing is a silver figure-eight design; the lighter colored hind wings have dark margins.
Egg – The round, greenish-white egg is slightly smaller than a pinhead.
Larva – This green larva has three pairs of prolegs and several white stripes which run the length of the body. When fully grown, the caterpillar is less noticeably striped and measures 30 mm long. It moves in a characteristic "looping" motion (Figure P).
Pupa – The green or brown pupa is approximately 19 mm long and encased in a loosely woven cocoon.
Distribution – Native to North America, the cabbage looper is common from southern Canada into Mexico. In the United States, this caterpillar is primarily a problem in the south.
Host Plants – The cabbage looper infests a large range of plants. Some cultivated hosts include: cabbage and related plants, cotton, potato, spinach, lettuce, celery, parsley, tomato, and soybean. Collards and cotton are preferred over broccoli, cauliflower, or cabbage for oviposition.
Damage – Cabbage looper feeding injury closely resembles that of the imported cabbageworm. The young caterpillars feed on the undersides of leaves. As the larvae mature, they move to more protected areas deeper within cabbage heads. These larger larvae feed between leaf veins as they progress from the outer to the inner leaves.
Life History – Cabbage loopers overwinter as pupae in Florida and adjacent states. The inconspicuous night-flying moths emerge in spring, and females soon begin depositing 275 to 350 eggs, singly, on the upper surface of leaves. Several days later, young loopers hatch from the eggs and begin feeding. The caterpillars consume foliage voraciously for 2 to 4 weeks before spinning cocoons on the host plant foliage and pupating. Within 2 weeks the next generation of moths emerge. There are three or more generations each year in North Carolina.
The use of resistant cabbage varieties such as Mammoth Red Rock, Chieftan Savoy, and Savoy Perfection Drumhead helps reduce cabbage looper damage. On most crucifers, however, chemical control of this pest becomes necessary.
Insecticides for control of the cabbage looper are most effective on young and exposed larvae. A 7-day spray schedule is usually recommended for caterpillar control on crucifers. For recommended chemicals and rates, consult the current North Carolina Agricultural Chemicals Manual.
Cabbage maggot, Hylemya brassicae (Weidemann), Anthomyiidae, DIPTERA
Adult – This fly resembles a common house fly although it is somewhat smaller. It is gray with three distinct black stripes on the thorax, a dark stripe along the top of the abdomen, and is 5 to 6 mm long. The eyes are reddish-purple.
Egg – The white, finely ridged egg is about 1 mm long.
Larva – The white, legless maggot has a pointed head and grows to a length of 6 mm.
Pupa – About the size of the adult, the pupa is enclosed in a hard brown puparium.
Distribution – Introduced from Europe, the cabbage maggot is most injurious in Canada and the northern United States. It has been a problem in Illinois and western North Carolina but is rarely serious any further south. In North Carolina cabbage maggots have been reported from practically all mountain counties west of a line from Polk County to Surry County and usually do not occur below 914 meters (3,000 feet) elevation.
Host Plants – The cabbage maggot feeds primarily on crucifers such as cabbage, cauliflower, broccoli, Brussels sprouts, collards, kohlrabi, radish, and turnip. Beet, cress, and celery have also been infested.
Damage – Cabbage maggots eat small fibrous roots and tunnel in stems and large fleshy roots. Tunnels where maggots have fed become brown and slimy, and organisms are likely to be introduced at these points. Plants attacked in the plant bed or soon after setting in the field fail to develop normally. Cabbage first takes on a sickly gray-blue color. Other infested crucifers may appear stunted or pale in color. If severe damage has been done, plants may wilt and die during the heat of the day. Infestations are difficult to detect in radishes and turnips because the tunneling of maggots in these large-rooted crops does not cause the foliage to wilt. Damage to these crops can be determined only by pulling some plants early and inspecting them. Cabbage maggots are usually most severe when the weather is cool and wet for a long period of time.
Life History – Cabbage maggots overwinter as pupae 2 to 13 cm deep in the soil. As the soil warms in spring, adult flies emerge from cocoons, feed on the nectar of flowers, and mate. Appearing as early as April, females soon begin depositing eggs in the soil at or near the base of host plants. Three to 7 days later, young maggots emerge from the eggs and move into the soil searching for roots upon which they feed for 3 to 4 weeks before pupating. Pupation may take place within root burrows or out in the soil and usually lasts 2 or 3 weeks. The second generation of adults appears in late June or early July. At least three generations occur annually in North Carolina.
Cultural practices such as late planting, careful selection of seedbed location, and elimination of weedy hosts can help prevent severe infestations. If planting is delayed until the last week of May or first week of June, few flies will be present to deposit eggs. Seedbeds located as far as possible from growing areas and protected from egg-laying flies with a gauze cloth will less likely be infested. The use of transplants grown in North Carolina at elevations below 3,000 feet will eliminate the danger of introducing the maggots on infested transplants. The fall destruction of turnip and cabbage stumps and weeds such as wild mustards will eliminate many larvae or pupae associated with these plants. Proper fertilization, irrigation, and good soil practices also lessen maggot damage by improving plant tolerance.
Cabbage maggots often require chemical control. An insecticide can be broadcast and incorporated just prior to planting seed or setting transplants. The application of a drench after setting transplants may also be effective. For recommended insecticides and rates, consult the current North Carolina Agricultural Chemicals Manual.
Cabbage webworm, Hellula rogatalis (Hulst), Pyralidae, LEPIDOPTERA
Adult – The moth has brownish-yellow forewings mottled with darker brown and pale gray hind wings. The wingspan is only slightly more than 13 mm. Resting on the ground where it is well camouflaged, the moth takes short, erratic flights when disturbed.
Egg – Oval and about 1 mm long, the egg is grayish-white at first, later acquiring a pinkish hue.
Larva – The first instar larva has a pale yellowish-gray body about 1 mm long with a dark, wide head. The mature larva is also yellowish-gray but has five dark longitudinal stripes with moderately long yellow and light brown hairs and is 13 to 15 mm long. The black head has a well-defined V-shaped mark.
Pupa – The yellowish-brown pupa is 6 to 7.5 mm long, 2 mm wide and occurs within a cocoon about 9 mm long made of silk and soil particles.
Distribution – Primarily a problem in southern states, the cabbage webworm occurs from North Carolina south to Florida and westward into California.
Host Plants – Most crucifers and some closely related weedy plants are attacked by cabbage webworms. Hosts include cabbage, turnip, beet, collard, cauliflower, kale, rutabaga, radish, kohlrabi, mustard, rape, horseradish, shepherdspurse, and purslane.
Damage – In North Carolina cabbage webworms do no damage to spring cole crops. In late summer or early fall, however, young plants of the fall crop are subject to attack. By boring into buds, stems, and stalks, webworms destroy or disfigure buds and sometimes kill entire plants. Plants with destroyed buds will produce secondary buds but these are not likely to mature into marketable heads by harvest.
Webworms feeding on the outer leaves of older plants are harmless. Webworms are enclosed by protective silken webs, often hiding along leaf veins on the underside of leaves. They feed during the day, but are fairly inactive during cold weather.
Life History – Little information is available concerning the life history of the cabbage webworm in the southern United States. Closely related species overwinter as larva or pupae in silk-lined cells in soil. Cabbage webworm moths deposit approximately 300 to 350 eggs on host plant buds. About 3 days later, larvae emerge and feed in the buds, eventually moving to the outer leaves where they spin webs and continue to feed along large leaf veins. They pupate among shed leaves or other refuse on the ground. The number of annual generations in North Carolina has not been determined.
Cabbage webworm control is not necessary on spring-planted crucifers. On fall-planted crucifers, control is primarily preventive. Plants should be sprayed or dusted as soon as they come up or are set out. For recommended insecticides and rates, consult the current North Carolina Agricultural Chemicals Manual.
Cross-striped cabbageworm, Evergestis rimosalis (Guenee), Pyralidae, LEPIDOPTERA
Adult – The yellowish-brown moth has a body about 10 mm long and a wingspan of about 25 mm. The mottled forewings are marked with dark brown zig-zag lines; the pale hind wings have 5 or 6 small dusky spots between the middle of the wing and its inner border.
Egg – The egg mass, laid on the foliage, consists of thin, oval, flattened eggs which overlap like fish scales. Each individual yellow egg is about 1.2 mm long and 1 mm wide.
Larva – Only a few millimeters long when newly hatched, the first instar larva has a large head and uniformly gray body sparsely covered with hairs. A mature larva has a bluish-gray body up to 20 mm long with tiny black transverse stripes. A black stripe with a yellow stripe underneath it runs along each side of the body. The underside of the larva is green mottled with yellow (Figure J).
Pupa – The yellowish-brown to dark brown, 11- to 12-mm-long pupa can be found in a light gray cocoon with particles of sand enmeshed. The cocoon itself is about 16 mm long and 10 mm wide.
Distribution – Cross-striped cabbageworms have been reported in many states from Delaware and Nebraska southward. Moths have been taken farther north, but this insect is believed to be primarily southern in distribution.
Host Plants – Cabbage, turnip, and related plants are the only known hosts of this pest.
Damage – Because eggs are deposited in masses, individual plants may be infested with large numbers of cross-striped cabbageworms. These caterpillars feed on all tender plant parts but prefer terminal buds. Young leaves and buds are often riddled with holes (Figure K).
Life History – No biological studies of this pest have been conducted in North Carolina, but in Washington, DC, the cross-striped cabbageworm is reported to produce four generations per year. They probably overwinter as larvae and pupate in spring. Pupation occurs just below the soil surface and lasts about 6 days. Moths emerge from pupae and soon deposit eggs in masses of 20 to 30 on the underside of leaves. Under warm, favorable conditions, eggs hatch in about 6 days. Larvae develop in about 2 to 3 weeks in summer, but require longer to develop during cooler periods of weather.
For recommended insecticides and rates, consult the current North Carolina Agricultural Chemicals Manual.
Diamond moth, Plutella xylostella (Linnaeus), Yponomeutidae, LEPIDOPTERA
Adult – This grayish-brown moth has narrow forewings, conspicuously fringed hind wings, and an 18 mm wingspan. When at rest, the wings of the male come together to form a line of white or pale yellow diamonds down the middle of the back (Figure R).
Egg – The minute round egg is pale yellow.
Larva – Tapering slightly at both ends, this pale green larva with a black head and scattered black hairs reaches a length of 7 mm when mature (Figure R). It wriggles rapidly when disturbed, often dropping from the plant and hanging by a silk-like thread.
Pupa – The yellowish pupa is enclosed within a loosely spun, gauze-like cocoon measuring about 7.5 mm in length.
Distribution – A native of Europe, the diamondback moth can be found throughout the United States and in all areas of the world where cole crops are grown. It can be a problem in greenhouses also.
Host Plants – The diamondback moth is a pest of practically all crucifers, including cabbage, broccoli, cauliflower, collards, kale, brussels sprouts, kohlrabi, turnip, radish, mustard, and watercress.
Damage – Diamondback moth larvae feed on all plant parts, but prefer the undersides of older leaves, crevices between loose leaves, and young buds. They eat small holes in leaves and buds, or feed superficially leaving slight perforations instead of holes. When populations remain low, these small caterpillars cause little damage; however, in large numbers they are particularly injurious to young plants. Heavy feeding on buds may cause the marketable portion of the plant to fail to develop properly.
Life History – Diamondback moths overwinter as adults among field debris of crucifer crops. In spring, eggs are laid, singly or in groups of two or three on foliage. Larvae, which hatch from eggs a few days later, feed for about 10 days during warm weather and a month during cool seasons. Larvae first feed as leafminers but soon emerge and infest the undersides of leaves. Once mature, larvae spin loose cocoons which remain attached to lower leaf surfaces. After a 2-week pupal period, a new generation of moths emerge. In temperate regions, the diamondback moth has 2 to 6 or more generations each year. Five or 6 generations per year are common in North Carolina.
Since these moths overwinter in the field, destroying or plowing under crop debris is a recommended cultural practice. Planting resistant varieties also reduces infestation. The following crucifer varieties are less attractive to diamondback moth larvae: Michihli Chinese and Mammoth Red Rock (cabbage); Southern Giant Curled (mustard); Seven Top and Purple Top White Globe (turnip); Vates (kale); and Cherry Belle, White Icicle, Globemaster, and Champion (radish).
Diamondback moth caterpillars are controlled by the same insecticides used against other caterpillars on crucifers. For recommended insecticides and rates, consult the current North Carolina Agricultural Chemical Manual.
Harlequin bug, Murgantia histrionica (Hahn), Pentatomidae, HEMIPTERA
Adult – This black, shield-shaped bug is brightly colored with orange, red, and yellow markings (Figure N). It varies from 7 to 10 mm in length.
Egg – The barrel-shaped egg, about 1 mm long, is light gray or pale yellow. It has two black bands -- one at the top, the other near the bottom -- and a black spot just above the lower band. Eggs are laid in clusters on crucifer foliage.
Nymph – The oval nymph is similar to the adult in coloration, but is slightly smaller and lacks wings.
Distribution – Native to Central America and Mexico, the harlequin bug is now found from coast to coast in North America as far north as the Great Lakes and New England. It is most injurious, however, in the southern states and rarely causes damage north of latitude 40°N.
Host Plants – Harlequin bugs attack nearly all crucifers, including common weeds of the mustard family such as wild mustard, shepherdspurse, peppergrass, bittercress, and watercress. If infestations are heavy and food becomes scarce, harlequin bugs will also feed on squash, corn, bean, asparagus, okra, and tomato.
Damage – Adults and nymphs pierce stalks, leaves, and veins with their needle-like mouthparts and extract plant juices (Figure O). Stems and leaves injured in this manner develop irregular cloudy spots around the puncture wound. Young plants are likely to wilt, turn brown, and eventually die; while older plants are only stunted.
Life History – Harlequin bugs overwinter as adults throughout most of their range. They remain active throughout the mild winters of the Gulf States, but hibernate among plant debris during the harsh winters of northern states. Adults emerge early in spring. Approximately 2 weeks after resuming activity, females begin depositing eggs on the undersides of leaves. Eggs are laid in double-row clusters of 10 to 13 until each female has deposited approximately 155 eggs. In early spring, eggs hatch in about 20 days. Eggs hatch in 4 to 5 days as the weather becomes warmer. Nymphs feed for 6 to 8 weeks and develop through 5 instars before becoming adults. Two to four generations occur each year in North Carolina.
Populations of overwintering adults can be reduced by plowing under field debris after the onset of cold weather. Destruction of weeds within fields and along fence rows also limits overwintering sites. In addition to cultural practices, resistant varieties should be planted when possible. The following varieties are recommended: Copenhagen Market 86, Headstart, Savoy Perfection Drumhead, Stein's Flat Dutch, and Early Jersey Wakefield (cabbage); Green Glaze (collards); Early Snowball X and Snowball Y (cauliflower); Red Devil, White Icicle, Globemaster, Cherry Belle, Champion, and Red Prince (radish).
For chemical control of harlequin bug infestations, insecticides should be applied when bugs first appear and applications repeated as necessary. For recommended insecticides and rates, consult the current North Carolina Agricultural Chemicals Manual.
Imported cabbageworm, Pieris rapae (Linnaeus), Pieridae, LEPIDOPTERA
Adult – Both sexes of this white butterfly have a black area near the tip of each forewing and a small black spot on the front edge of each hind wing. The female has two black spots on each forewing while the male has only one. The female has a wingspan of about 50 mm; the male is slightly smaller.
Egg – The pale yellow, bullet-shaped egg, about 1 mm long, is ribbed lengthwise and crosswise and is attached endwise to the leaf surface.
Larva – The velvet-like green larva has a faint yellow stripe down its back, a row of faint yellow spots on each side, and five pairs of prolegs (Figure L). When fully grown, it measures about 32 mm long.
Pupa – The sharply-angled pupa, or chrysalis, is gray, green, or brown and about 20 mm long. It is attached to the lower leaf surface by a silken loop.
Distribution – The imported cabbageworm has spread throughout the United States from coast to coast after introduction into Canada from Europe. In the Western Hemisphere, this butterfly is most common between latitudes 30°N and 60°N. It is equally destructive in the northern and southern areas of its range.
Damage – Imported cabbageworms are commonly found on the undersides of leaves. Like cabbage loopers, young caterpillars feed superficially, leaving the upper surface intact. Larger larvae leave holes in the leaves and are more likely to eat through small veins than are loopers. In contrast to cabbage loopers, imported cabbageworms bore into the center of the head thereby doing more damage to the edible portion of the plant. The presence of masses of wet, greenish-brown excrement deep among leaves is indicative of this pest.
Life History – Imported cabbageworms overwinter as pupae attached to host plant debris. Adults emerge early in spring, as early as March even in the northern states. Soon after mating, females begin depositing eggs singly on cultivated host plants, if available . Often, however, the first generation of cabbageworms is raised on wild hosts. After hatching 4 to 8 days post egg-deposition, larvae feed and develop through five instars in 10 to 14 days. When mature, larvae fasten themselves to lower leaf surfaces by silk bands. During spring and summer, the pupal stage lasts 7 to 12 days before a new generation of butterflies emerges. There are usually 3 or 4 generations each year.
Although cabbageworms are subject to attack by a number of disease organisms and parasites, a combination of cultural and / or chemical control practices are necessary. The use of resistant cabbage varieties, such as Mammoth Red Rock, Chieftan Savoy, and Savoy Perfection Drumhead, provides some protection but not complete control. New plantings should be as far as possible from those of the previous season. At the end of the season, crops should be harvested without delay. Plowing under or destroying plant residues at this time eliminates an important food source for the overwintering generation of cabbageworms.
Insecticide applications should begin when the cabbageworm population reaches a threshold of one worm per plant. Sprays then should be repeated every 5 to 7 days, as needed. For recommended insecticides and rates, consult the current North Carolina Agricultural Chemicals Manual.
Striped Flea Beetle
Striped flea beetle, Phyllotreta striolata (Fabricius), Chrysolmelidae, COLEOPTERA
Adult – This small black beetle, 1.5 to 2.5 mm long, has a wavy yellow line running the length of each wing. The hind legs are thickened, enabling the beetle to jump.
Egg – The minute, oval to elongate egg is white.
Larva – When fully grown, the white, brown-headed larva is 3.2 to 5.0 mm long. It has 3 pairs of tiny legs near its head.
Pupa – The tiny white pupa is approximately the same size and shape as the adult.
Distribution – The striped flea beetle is common throughout the eastern and Pacific areas of the United States and is Eurasian in origin. It is not common in much of the Rocky Mountain regions.
Host Plants – Striped flea beetles infest many crucifers but prefer mustard, turnip, radish, and related weeds.
Damage – Although larvae feed on the roots of host plants, the primary damage is caused by adult beetles feeding on foliage. Beetles make small pits in leaves (Figure Q). The remaining thin layers of tissue eventually dry up and fall away leaving small "shot holes" in the foliage. This type of injury is capable of killing young plants. In addition, beetles may act as vectors of plant disease.
Life History – Striped flea beetles overwinter among debris in and around fields. Emerging early in spring, they attack seedlings and young plants. Eggs are deposited in tiny crevices gnawed out of the base of host plant stems. About 10 days later, grubs hatch from the eggs and move into the soil to attack roots. After feeding for 3 or 4 weeks, the larvae pupate for 7 to 10 days. A new generation of beetles then emerges. There are at least two generations each year in North Carolina.
Cultural practices and the use of resistant varieties help prevent severe flea beetle infestations. Stripes of gauze physically protect seedbeds from flea beetles. Good weed control and the destruction of crop residue reduce overwintering populations. The use of resistant varieties may reduce injury by existing beetles. Such varieties include: Stein's Early Flat Dutch, Mammoth Red Rock, Savoy Perfection Drumhead, Early Jersey Wakefield, Copenhagen Market 86, and Ferry's Round Dutch (cabbage); Vates and Georgia (collards); Florida Broadleaf (mustard); American Purple Top (Rutabaga); Snowball A and Early Snowball X (cauliflower); DeCicco, Coastal, Italian Green Sprouting, and Atlantic (broccoli); Vates, Dwarf Siberian, Dwarf Green Curled Scotch, and Early Siberian (kale).
Chemical treatments for control of flea beetles should be applied as needed. For recommended insecticides and rates, consult the current North Carolina Agricultural Chemicals Manual.
Variegated cutworm, Peridroma saucia (Hubner), Noctuidae, LEPIDOPTERA
Adult – The forewings of this moth are yellow or brown with pale mottled designs, while the hind wings are white with brown veins and margins. The wingspan varies from 3.8 to 5.0 cm.
Egg – The spherical white or pale yellow eggs are ribbed and slightly less than 1 mm in diameter. They are laid in irregular elongate patches and turn brown before hatching.
Larva – The smooth-skinned larva is pale gray or light brown mottled with dark brown. The first three abdominal segments bear two yellow or orange dots while the eighth segment is marked with a dark "W." The mature larva may be as long as 40 mm and curls into a C-shaped ball when disturbed.
Pupa – The reddish-brown pupa is 15 to 20 mm long.
Distribution – The range of the variegated cutworm spans most of North America including Canada and Alaska and extends into South America. It is also found in Europe and the Mediterranean area. Although it is of most importance in the Pacific Northwest and some northeastern states, this cutworm is an occasional pest in North Carolina, especially in areas with sandy or sandy loam soils.
Host Plants – The variegated cutworm feeds on a variety of garden crops, trees, vines, grasses, field crops, ornamentals, and greenhouse plants.
Damage – Beginning in early spring and continuing throughout summer, variegated cutworms climb host plants and devour foliage, buds, and fruit. Damaging infestations, however, are sporadic. Because the variegated cutworm is one of the few cutworm species that climb plants to feed, its presence is usually more noticeable than that of subterranean cutworms. Late larval instars, however, burrow in the soil and cut off plants at or near the soil surface.
Life History – Variegated cutworms overwinter as pupae with a high percent mortality occurring during this life stage. Female moths emerging from surviving pupae compensate by laying over 2,000 eggs during their short life span. Clusters of 60 or more eggs are deposited on stems or leaves of low-growing plants as well as on fences and buildings. During summer, eggs usually hatch in 5 days. The active larvae feed at night and on cloudy days for about 31⁄2 weeks before burrowing into soil to pupate. The pupal stage lasts two weeks to a month before second generation moths emerge. Requiring 48 days to complete a life cycle, variegated cutworms produce two to four generations each year. The exact number of annual generations produced in North Carolina is not known.
For recommended insecticides and rates, consult the current North Carolina Agricultural Chemicals Manual.
Vegetable weevil, Listroderes costirostris obliquus (Klug), Curculionidae, COLEOPTERA
Adult – The female adult weevil is about 6.4 mm long with a short, stout snout. It is dull grayish-brown with a light V-shaped mark on the wing covers.
Egg – The egg is elliptical, 0.5 mm in diameter, and creamy white when first laid. It becomes black before hatching.
Larva – The pale green, legless larva has a dark mottled head and is about 1 cm long when fully grown.
Pupa – The pupa is pale yellow at first and later turns brown. It is similar in shape to the adult, with snout, legs and wing pads folded vertically along the body. It is about 7.9 mm long.
Distribution – The vegetable weevil, originally from South America, was first reported in this country in 1922. It now occurs in the Gulf and southern states and in Oklahoma, Arizona, and California. In North Carolina the vegetable weevil occurs throughout the state but is generally more common in the southern Coastal Plain.
Host Plants – The vegetable weevil feeds on a wide range of cultivated crops: turnip, carrot, collards, mustard, tomato, potato, tobacco, clary sage, and also a number of weeds.
Damage – Larval and adult vegetable weevils attack foliage and roots of a number of vegetable crops, often injuring seedlings or newly set plants. Plants attacked underground are usually large-rooted crops like carrot and turnip. When larvae feed on buds, growth may be stunted. Irregularly shaped holes in the leaves are indicative of this pest.
Life History – The adult vegetable weevil is active during fall, winter, and spring and aestivates (enters dormancy) during the summer in trash, leaves or grass at the edge of fields. Reproduction is parthenogenetic (no males, females lay eggs which develop into females) and some individuals may live 2 years. After coming out of aestivation, adults feed for several days to a month before depositing eggs on turnips or collards. Oviposition begins in fall and may continue into spring of the next year. Hatch occurs after an incubation period of 2 or more weeks depending on the temperature. Larvae feed on various crops and become full grown in 23 to 45 days. They then excavate earthen cells in the soil and pupate. Pupation, which may occur in spring or in fall and late winter, lasts from a few days to 2 weeks depending on temperature. Adults emerge from January to June. The length of time from egg hatch to adult emergence may vary from 1 to 4 months. There is one generation per year.
Cultivation in fall and winter is important in reducing populations. Insecticides are also available for control of the vegetable weevil. For specific recommendations, consult the current North Carolina Agricultural Chemicals Manual.
Publication date: Feb. 10, 2003
Other Publications in Insect and Related Pests of Vegetables
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