PESTS OF COTTON


North Carolina Cooperative Extension
Extracted from INSECT and related PESTS of FIELD CROPS (AG-271)
Dated 5/82
Placed on the Web 10/94 by the Center for Integrated Pest Management, NCSU

In 1980, cotton was planted on 25,506 hectares (63,000 acres) of North Carolina farm land. Cleveland County, the Scotland-Robeson counties area, and the Northampton-Halifax-Edgecombe counties area produce 90 percent of the cotton in North Carolina. Insects are an important factor in cotton production here but only the bollworm and the boll weevil are considered limiting. A pest management approach of varying degrees of sophistication has been applied for insect control in all cotton-producing areas of our state.

Key to Pests of Cotton

A. Insect and mite pests which pierce or rasp plant tissue to extract sap (Fig. A to D).

  1. Aphids - Usually feeding in colonies, these yellow, green or black, pear-shaped insects (Fig. A above) may be as long as 2 mm and may or may not have wings. Infested leaves curl and pucker; heavily infested seedlings become stunted and die. A black mold, which grows on the sticky, sugary "honeydew" that aphids excrete, is often evidence of aphid infestation.

    1. Cotton aphid - This aphid is usually yellow in the summer and pale or dark green in cooler seasons.

    2. Cowpea aphid - The adult of this species is black with white appendages. The nymph is pale gray with a powdery coating.

  2. Tarnished plant bug - Approximately 6.4 mm long, this oval-shaped, brown lygus bug (Fig. B above) has long legs, long antennae, and a white triangle between its "shoulders." It extracts sap from terminals, squares, flowers, and bolls, causing young fruiting forms to be shed. Infested flowers and bolls may open prematurely.

  3. Thrips - Several species of these yellow, orange, brown, or black rasping insects (Fig. C above) attack seedling cotton. Foliage infested by these tiny, fringed-wing insects becomes distorted and curls upward; terminal buds are sometimes killed.

  4. Twospotted spider mite - The almost microscopic, eight-legged, adult female mite is yellowish (Fig. D above) to dark green with 2 or 4 dark spots on its back. The immature mite may have 6 or 8 legs. Feeding on the underside of the leaf, this mite extracts sap, causing the upper leaf surface to have a whitish or bronze cast. Severe infestations can result in defoliation and loss of plant vigor. Silken webs are common on the underside of infested leaves, particularly along the large leaf veins.

B. Caterpillars that chew or mine the foliage or sever seedling stems.

  1. Armyworms - These smooth-skinned, variously colored caterpillars have 5 pairs of prolegs, are occasionally problem foliage pests, and may be difficult to control chemically.

    1. Beet armyworm - This dark-headed (Fig. A above), green or black larva sometimes has 3 longitudinal, light stripes and usually attains a length of 25 to 30 mm. A small black spot occurs on each side of the second segment behind the head (Fig. B above). This larva normally skeletonizes foliage but at times feeds on squares, blooms, and bolls causing economic loss to cotton.

    2. Fall armyworm - Although this green, brown, or black caterpillar primarily attacks blooms, squares, and bolls, it also feeds on the foliage, occasionally tops plants, and bores into stems. This larva has 5 pairs of prolegs, reaches a maximum length of 40 mm, and often has distinct inverted "Y" on its head capsule (Fig. C above). It has a black, longitudinal stripe down each side of its body and a yellowish-gray stripe down its back.

    3. Yellowstriped armyworm - Reaching a length of up to 45 mm, the smooth-skinned, pale gray to jet black caterpillar has a yellowish-orange stripe along each side and a pair of black, triangular spots on the back of most segments (Fig. D above). Like the fall armyworm, this larva often has a pale but distinct inverted "Y" on its head capsule (Fig. E above). This insect rarely reaches damaging levels on cotton but is most injurious to seedlings.

  2. Cabbage looper - Reaching a length of about 40 mm, this green caterpillar has 3 pairs of prolegs and several longitudinal, white stripes. Its body tapers from rear to front. Its feeding leaves ragged holes in the foliage.

  3. Cutworms. These fat caterpillars reach a length of 40 or 45 mm and have 5 pairs of prolegs. They display a variety of feeding habits and curl up when disturbed. They sever seedling stems and occasionally feed on leaves.

    1. Black cutworm - The skin of this light gray to black cutworm is granulated, the granules resembling rounded, flattened pebbles (Fig. A). The caterpillar cuts seedlings off at the soil line during the night. It commonly pulls the cut stem of a seedling into the entrance of its burrow and feeds on it during the day.

    2. Granulate cutworm - This cutworm has a pale brown head, a dark brown band down its back and brown sides with faint stripes. The skin granules of this cutworm are like blunt cones as high as they are wide (Fig. B). The caterpillar also severs seedlings near the soil line at night.

    3. Variegated cutworm - Although primarily damaging to seedling stems, this species is a climbing cutworm and may feed on foliage. Its smooth-skinned body is pale gray to dark brown with a row of orange or yellow spots down the middle of its back. A black spot and a yellow spot occur on the eighth abdominal segment.

C. Insects that feed in squares or bolls.

  1. Boll weevil larva - The white-bodied, brown-headed, legless grub (Fig. A), up to 13 mm long, feeds within squares or small bolls, destroying the contents.

  2. Boll Weevil adult - About 8.5 mm long, the reddish-brown or gray adult weevil (Fig. B) has a distinctive characteristic: a double-toothed spur on the inner surface of each front leg. The female punctures squares and young bolls to lay eggs. These nipple-like egg punctures are about 1 mm in diameter. Egg-punctured squares flare and fall to the ground where larval development is completed.

  3. Caterpillars - These moth larvae have 3 pairs of short legs near the head and 5 pairs of prolegs.

    1. Bollworm complex - When fully grown, these larvae are green, reddish, or brown with pale, longitudinal stripes and scattered, black spots. Early instars are cream colored or yellowish-green with few markings. Larval instars vary from 1.5 to 44 mm in length and have 5 pairs of prolegs. The contents of squares or bolls may be completely consumed by bollworms. Cotton lint development is reduced and rot organisms may gain entrance into the bolls that are only partially damaged.

    2. Fall armyworm - See Section B.1.b. of this key for description. This caterpillar may bore into stems and bolls like the bollworm, but typically enters the boll at the tip or at the base next to the stem.

    3. Yellowstriped armyworm - See Section B.1.c. of this key for description. This larva occasionally bores into squares or bolls but is rarely an economic problem.