Pink Bollworm

Pink bollworm is a major pest of cotton in southern California deserts. While apparently established in the San Joaquin Valley, economic infestations have not occurred in this area. Adults are small, grayish brown, inconspicuous moths. When their wings are folded, they have an elongated slender appearance. The wing tips are conspicuously fringed. Young larvae are tiny, white caterpillars with dark brown heads. When mature, they are about 0.5 inch long and have wide transverse pink bands on the back. To be able to see pink bollworm larvae, bolls have to be cracked open. The first and second instars are difficult to see against the white lint of the bolls. Eggs are very small, slightly elongated, and laid under the calyx of green bolls.

Pink bollworms damage squares and bolls, the damage to bolls being the most serious. Larvae burrow into bolls, through the lint, to feed on seeds. As the larva burrows within a boll, lint is cut and stained, resulting in severe quality loss. Under dry conditions, yield and quality losses are directly related to the percentage of bolls infested and the numbers of larvae per boll. With high humidity, it only takes one or two larvae to destroy an entire boll because damaged bolls are vulnerable to infection by boll rot fungi.

When high population levels of pink bollworm occur, the objectives of management are to keep infestations below damaging levels in the current season—without creating secondary outbreaks of other pests—and to reduce the overwintering population that will threaten the following season's crop. The main control tools are observance of host-free period (San Joaquin Valley), the judicious use of insecticides, timely crop termination and harvest, rapid crop destruction, properly timed winter and spring irrigations, and compliance with plowdown requirements. When pink bollworms are found in the San Joaquin Valley, a regional monitoring and sterile moth release program is implemented.

Because of the danger of secondary outbreaks, especially in the low desert valleys, it is wise to limit insecticide treatments to those periods when susceptible bolls are present and when sampling shows the percentage of infested bolls is above the treatment threshold. It is rarely necessary to apply insecticides against moths from the overwintered population of pink bollworm and, often, treatments are not needed against the first generation of moths that develop from larvae within squares. Be alert, however, for high populations of pink bollworm moths when squares are developing, especially if other pests such as lygus bugs and armyworms are also threatening. Mating disruptants and sterile moth releases, on the other hand, are most effective when aimed at the overwintering generation, usually about the time cotton plants have 6 to 8 leaves.

The use of Bt cotton will help prevent damage by pink bollworm. A recently developed transgenic cotton, Bollguard II, offers suppression of cotton bollworm, along with beet armyworms, pink bollworm, and tobacco budworm.

Eliminate the food supply for pink bollworm by cutting off irrigation early enough to stop production of green bolls by early September. Regardless of when the crop is terminated, immediately shred the cotton plants following harvest. Shredding destroys some larvae directly and promotes rapid drying of unharvested bolls. If fall temperatures are high during September and much of October, leave crop debris on the soil surface for two or more weeks after the shredding operation to further destroy larvae. Be sure to comply with plowdown requirements and cross disc or plow to a depth of at least 6 inches. In the San Joaquin Valley, there is a 90-day host-free period that extends from plowdown to March 10.

Winter irrigations can reduce populations of overwintering pink bollworms by as much as 50 to 70%; flooding in December is more effective than flooding in November or January. Take advantage of pink bollworm mortality afforded by winter irrigations and rotate to small grains or newly seeded alfalfa.

In spring, irrigations can also be used to promote early spring emergence of pink bollworm. If cotton is being followed with cotton, preirrigate in February and plant as early as possible, following guidelines to ensure adequate soil temperature for germination and emergence. Plan irrigations of the crop to prevent even slight moisture stress and to promote maximum emergence of moths in advance of susceptible squares.

Cultural controls, with the exception of the use of Bt cotton and the use of mating disruption and sprays of the Entrust formulation of spinosad are acceptable to use on organically grown cotton.

In the San Joaquin Valley, pink bollworm is primarily managed with a host-free period. In Southern California, sampling bolls is the most reliable way to monitor pink bollworm populations. See Integrated Pest Management for Cotton, 2nd edition, for detailed sampling methods and thresholds. The use of gossyplure, a sex attractant that disrupts mating when distributed throughout the field, may be effective against pink bollworm when it is supplemented with cultural control practices that minimize the number of overwintering bollworms.

Do not apply insecticides to control larvae; larvae are either inside the boll or in the ground and therefore insecticide contact is difficult.