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Cotton Insect Management

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Scouting • Cutworms • Thrips • Plant Bugs • Boll Weevil • Bollworm and Tobacco Budworm • Banded Wing Whiteflies • Cotton Aphids • Spider Mites • Loopers • Armyworms • Stink Bugs • Insect Treatment Levels for Narrow Row Cotton -- 30-inch Row Spacing

Effective management and control of cotton insects requires not only knowledge of their life cycles and biology but also understanding of the methods used in determining insect populations in the field. Timely scouting of fields, preferably twice weekly, provides information on the cotton plant and cotton insect populations. 

Use treatment guidelines to determine the need for insecticides. Beneficial insect populations are greatly reduced by single applications or destroyed by several applications. Insecticides applied unnecessarily often generate bollworm, aphid or spider mite problems because of reduced beneficial populations. 

Scouting

Scouting involves monitoring insects throughout the season to determine population levels. The point sample scouting method used in Arkansas includes a whole plant search for bollworm and boll weevil, fruit counts, the shake cloth for monitoring plant bugs and the small square set to determine fruit set and plant bug activity. Further details on insects and cotton scouting are available in Extension Circular 561 (Scouting Manual). 

Insect Management

Cutworms

Several cutworm species attack cotton in the seedling stage. Symptoms of damage are wilted plants or plants cut off at the ground. Larvae usually feed at night and hide in the soil or under leaf trash during the day. The larvae vary in color, are often greasy-looking and curl up into a ball when touched. The primary damage by cutworms is stand loss. 

Thrips

Several thrips species attack cotton upon emergence in the spring. Thrips are very small insects that may be seen if plants are shaken over a thrips box. Adults and nymphs feed on young leaves, terminals and other tender plant structures. Ragged, crinkled leaves that curl upward with a silvery appearance on the underside are typical symptoms of thrips damage to young cotton. Damage is primarily to seedling cotton, and heavy damage may stunt and delay growth. This damage may cause reduced yield, even though the cotton plant eventually outgrows visible damage. Thrips damage may contribute to a reduction in stand. 

Treatments for thrips may be applied as seed treatments, at plant-ing in-furrow as a systemic insecticide or after emergence as a foliar spray. Apply foliar sprays before the first or second true leaf begins to emerge. Thrips adults and nymphs feed inside the rolled leaves of plant terminals. 

Plant Bugs
(Tarnished Plant Bug, Clouded Plant Bug and Cotton Fleahopper)

Three species of plant bugs attack cotton in Arkansas ­ tarnished plant bug or Lygus bug, clouded plant bug and the cotton fleahopper. These plant bugs do similar damage. Feeding is by a piercing/sucking mouthpart. The insects damage terminals, squares (especially small squares), small bolls and other tender plant parts by inserting their needle-like mouthpart into them. Small squares usually turn dark and drop off while bolls may develop abnormally. 

The adult tarnished plant bug is a general brown-colored insect with mottled, small, irregular white patches. The immature form or nymph is light green with five black dots on its back, long antennae and no wings. The nymph moves quickly and resembles the adult as it nears maturity. 

The clouded plant bug is slightly longer than 1/4 inch and larger than the tarnished plant bug. Adults have a mottled appearance with mixtures of gray, brown and yellow colors. The first segment of the hind legs is strikingly larger than the front legs. The top of the body is covered with small black hairs, and the legs and antennae have red bands. Young nymphs resemble tiny spiders with a small, hairy body and long legs. 

The adult cotton fleahopper is a small insect about 1/7 inch long and pale green in color with tiny, dark spots. Nymphs are white and translucent at first, then become pale green after feeding. Fleahoppers feed primarily on small squares and other tender plant parts. 

Scout for plant bugs at least weekly and preferably twice a week, especially during early squaring through peak squaring. Insecticide appli-cation should be considered when: (1) plant bug numbers reach a predetermined threshold based on fruiting or (2) the square damage or small square set is approaching an economic injury level and plant bugs are present. 

 

.Boll Weevil

The boll weevil is one of the most destructive insects that attack cotton if infestations are left uncontrolled. A thorough knowledge of the insect's biology is important for effective control.   

Boll weevils emerge from overwintering sites in the spring and enter cotton fields. When cotton begins to square, females begin to lay eggs. Eggs are deposited singly inside squares and young bolls. One female boll weevil lays an average of 150 eggs in two weeks. The development time from egg to adult averages about 22 days but may be as little as 16 days during midsummer. The eggs hatch in 2 to 4 days, and the larvae feed for 7 to 11 days before entering the pupal stage.   

Boll weevils damage cotton by feeding on squares and young bolls. This feeding causes some square shed. The most damage is done when eggs are laid inside squares and bolls. The eggs hatch and young weevils feed inside squares causing damage that usually results in square shed or boll lint damage.   

Spring Suppression of Boll Weevil 

Boll weevil population is generally lowest during spring emergence from overwintering sites. Boll weevil pheromone traps detect these low level populations. The number trapped determines the need for a pinhead square application of insecticide to suppress boll weevil populations. 

Boll Weevil Resistance Management Plan 

The boll weevil has become resistant to many insecticides used for its control. Pyrethroid insecticides are very effective in controlling boll weevil. Development of resistance to pyrethroid in Arkansas may be a reality unless steps are taken to delay or prevent resistance. A resistance management plan is outlined in the following table. 

Bollworm and Tobacco Budworm

Bollworm (Helicoverpa zea) and tobacco budworm (Heliothis virescens) are two different insects, but the larvae look identical when observed in the cotton field.  The adult stages are easily distinguishable. 

The life cycle of each insect is similar. The discussion that follows applies to both insects unless otherwise specified. 

Bollworm eggs are laid singly, usually in the terminal area and on other tender plant parts. However, eggs may be laid all over the plant, especially on blooms. Eggs are pearly white to a cream color and are about half the size of a pinhead. The eggs hatch into a small larva in 3 to 4 days. The life cycle for bollworms from egg to adult requires about 30 days on the average with the larva feeding for about 14 to 16 days. Newly hatched larvae first feed on terminals and young squares. Larger larvae feed on larger squares and on bolls. The greatest economic loss occurs when bollworm larvae feed on bolls. 

Natural enemies feed upon the eggs and young larvae of bollworms especially during the early part of the growing season. However, when bollworm populations reach treatment levels, time the insecticide to control eggs and small larvae. If properly timed, low dosages of selected insecticides and ovicides may effectively control the field population of bollworm larvae and eggs. Use an appropriate rate for larvae larger than first instar or 1/16 inch. 

Banded Wing Whiteflies

The whitefly adult is a small, white insect with three narrow brown bands across the wings. The immature whitefly is flat and scale-like, doesn't fly and is found on the underside of leaves. Cotton is damaged by adults and immature whiteflies sucking sap from the plant. Heavy populations may cause some defoliation. The whitefly larvae secrete honeydew that may accumulate on cotton lint when bolls are opening. Black, sooty mold that could stain the lint may develop on the honeydew. 

Cotton Aphids

Aphids may build up in cotton fields any time during the growing season. Aphids reproduce very rapidly during favorable conditions, and large populations may build up in a short time. A new generation may occur every 5 days during the warm summer months. Aphids damage cotton by sucking juices from the plant and secreting honeydew. High populations of young cotton cause the leaves to curl down or crinkle; plants may become stunted and die, especially when they are young. When infestations occur during the main fruiting period, the older leaves may turn yellow and shed. Squares and small bolls may drop off as a result of severe leaf shed. During late season, the secretion of honeydew falls on open cotton and the lint may be stained by a black sooty mold which develops on the honeydew-contaminated lint. 

Spider Mites

Spider mites may invade fields any time during the year. They generally move into fields from field borders which serve as overwintering sites. Spider mites build high populations in a relatively short time. Mites develop from an egg to an adult in 5 to 7 days during summer. Spider mites feed on plant juices causing small, yellow spots on the leaves, resulting in a speckled appearance. Leaves may turn reddish when the infestation becomes heavy or during dry weather. Areas in fields infested with spider mites may appear lighter in color or reddish from a distance.

Loopers

Cabbage and soybean looper larvae are light green with several white lines down the length of the body. The larva arches the body as it crawls, thus the name looper. The larvae feed entirely on foliage between the leaf veins leaving a net-like appearance. Severe feeding while immature bolls are in the field reduces yield significantly, whereas feeding damage late in the season may not cause yield loss. 

Armyworms

The beet armyworm and fall armyworm may occasionally cause damage to cotton fields. The eggs are laid in masses, and larvae may occur in high numbers. 

Beet armyworm larvae range in color from light green to dark olive green or black and average 1 1/4 inches long at maturity. The beet armyworm is a general feeder and feeds on foliage, squares, blooms and bolls. The larvae tend to feed in groups. Feeding results in cotton plants appearing ragged overall. Infestations of larvae may be spotty, occurring only in certain areas of the field. 

Fall armyworm larvae are light to medium brown and have a smooth appearance. The fall armyworm may be easily confused with the bollworm. However, the fall armyworm has an inverted "Y" on the front of its head that is cream colored in contrast to a darker brown head. The fall armyworm tends to feed primarily on bolls even when small larvae, but they will feed on squares and blooms. 

Stink Bugs

Several species of stink bugs can cause economic losses in cotton. The most important species are the green, brown and southern green stink bugs. Adults of the green and southern green stink bug are both green but can be differentiated by band color on antennae. Green stink bugs have black bands and southern green stink bugs have red bands on the antennae. Nymphs of the green stink bug have a striped abdomen, and nymphs of the southern green stink bug have a spotted abdomen. Adults of the brown stink bug are brown and without sharp spines on the "shoulders," and nymphs are a light brown to pale green color. After migrating into cotton from alternate hosts, these destructive pests feed on developing bolls during mid to late season. Feeding is done with piercing/sucking mouthparts and is concentrated on seeds and surrounding tissues. 

Insect Treatment Levels for Narrow Row Cotton – 30-inch Row Spacing

Insect treatment levels for aphids, thrips, whiteflies, cutworms, loopers and spider mites are the same on 30-inch as 38-inch row spacing. Since treatment levels for bollworm/tobacco budworm larvae, boll weevil and plant bugs are based on a per acre basis, the numbers will change. The percent square set will not change for plant bugs. 

Donald R. Johnson, Extension Entomologist
Glenn E. Studebaker, Extension Entomologist
Gus Lorenz, Extension Entomologist, IPM Coordinator
Jeremy K. Greene, Extension Entomologist

DR. DONALD R. JOHNSON, GLENN E. STUDEBAKER and DR. JEREMY K. GREENE are Extension entomologists, and DR. GUSTAV LORENZ is Extension entomologist, IPM coordinator. Johnson and Lorenz are headquartered in Little Rock, Studebaker is headquartered in Keiser and Greene is headquartered in Monticello. They are employees of the University of Arkansas Cooperative Extension Service. 

FSA2065-PD-2-02RV