How to Manage Pests
UC Pest Management Guidelines
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.
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.
Biological control and unfavorable weather generally reduce thrips populations before treatment is necessary and plants usually recover from thrips injury.
UC IPM Pest Management Guidelines: Dry