How to Manage Pests

UC Pest Management Guidelines

DESCRIPTION OF THE PESTS

Thrips are small insects, about 0.04 inch long. Adult thrips have two pairs of narrow wings which are fringed with hairs. Immature thrips are wingless, whitish to yellowish in color, and are most commonly found in buds, flowers, or on the underside of leaves. Adults emerge continuously throughout the warm months. Adults and immatures may be found in beans at any time during the growing season. Eggs are deposited in plant tissue and hatching occurs in about 5 days during the summer months; the immature stages take about 5 to 7 days to complete development.

DAMAGE

Thrips are most noticeable and of greatest concern on young seedling plants. Their feeding will make the plants look ragged because they feed on young leaves and buds. A common sign of a heavy thrips infestation is distorted leaves that turn brownish around the edges and cup upward. Usually the plants will grow away from the problem, just as they outgrow severe ragging resulting from wind damage. Foliage-feeding thrips are effective predators on early season spider mite infestations. Both adult and immature thrips may be found in spider mite colonies feeding on spider mite eggs.

MANAGEMENT

Biological control and unfavorable weather generally reduce thrips populations before treatment is necessary and plants usually recover from thrips injury.

Biological Control
Minute pirate bugs (Orius tristicolor) play a major role in controlling thrips populations.

Cultural Control
Thrips populations tend to build up on weeds. Cultivating nearby weedy areas before beans emerge will reduce the potential of a thrips problem when the weeds begin to dry out. Cultivating weedy areas after bean emergence will increase thrips problems.

PUBLICATION

UC IPM Pest Management Guidelines: Dry Beans
UC ANR Publication 3446
Insects and Mites
L. D. Godfrey, Entomology, UC Davis
R. F. Long, UC Cooperative Extension, Yolo County

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