How to Manage Pests

UC Pest Management Guidelines



Scientific Names:
Western flower thrips: Frankliniella occidentalis
Bean thrips: Caliothrips fasciatus

(Reviewed 5/13, updated 5/13)

In this Guideline:

Description of the Pests

Thrips are tiny, slender insects less than 0.06 inch (1.55 mm) long. Western flower thrips are by far the most common thrips on cotton and may be found all season. They are light colored; adults have clear, slender wings. The bean thrips occasionally appears on cotton in summer, usually at field edges. Immature bean thrips have orange or red spots at either side on the end of their abdomen; adults are usually dark with white bands on their wings.


Although western flower thrips feed on leaves and buds and may sometimes cause seedling leaves to become distorted, their benefits as predators of mites generally outweigh any damage they may cause. While infested seedlings may appear severely deformed, they will grow out of the damage rapidly with the onset of hot weather. In unusual seasons when cool spring weather persists into June, damage to terminals and squares may be severe, particularly in the northern cotton growing areas of the San Joaquin Valley (Merced County). In the low desert growing areas where Bt cottons are used, Delta Bt cotton appears to be more susceptible to damage by western flower thrips.

Bean thrips feed on the cotton plant and may cause mature leaves to turn coppery brown or red and lower leaves to drop. Bean thrips injury may resemble spider mite injury, but affected leaves are covered with tiny black specks, which are the feces of the thrips. Usually injury is confined to field borders.


No treatment is generally recommended for western flower thrips. Young plants will rapidly recover from injury. Insecticides applied to control flower thrips are usually counterproductive, as they tend to promote outbreaks of mites. Only in situations where a prolonged thrips infestation is destroying seedling terminals is treatment justified.

Bean thrips outbreaks most commonly occur where there are abandoned fields or pasture areas with an abundant growth of prickly lettuce and morningglory, or field bindweed. Control of these weeds will reduce the probability of an outbreak. Spot or strip treatments may occasionally be needed; the bean thrips is controlled by most insecticides used against lygus bug.

Some Californian upland cotton varieties appear to be more susceptible to thrips than Acala varieties. These susceptible varieties should be monitored more closely for thrips populations and damage.

Monitoring and Treatment Decisions

The critical time for monitoring thrips is from crop emergence through seedling stages. To improve the efficiency of your monitoring program, combine sampling of thrips with other pests. From crop emergence to seedling growth sample aphids, mites, and thrips together as described in MONITORING SPIDER MITES, APHIDS, AND THRIPS.

Common name Amount per acre** R.E.I.‡ P.H.I.‡
(example trade name)   (hours) (days)

Calculate impact of pesticide on air quality
Bee precaution pesticide ratings
The following are ranked with the pesticides having the greatest IPM value listed first—the most effective and least harmful to natural enemies, honey bees, and the environment are at the top of the table. When choosing a pesticide, also consider information relating to air and water quality, resistance management, and the pesticide's properties and application timing. Not all registered pesticides are listed. Always read the label of the product being used.
  (Orthene 97) 3 oz 24 21
  PERSISTENCE: Pest: Moderate NE:2 Moderate
  COMMENTS: Do not graze or feed trash to livestock. Apply in water at 5–10 gal spray/acre by air or 10–25 gal spray/acre by ground. May induce outbreaks of spider mites.
  (Radiant SC) 4.25–8.00 fl oz 4 28
  PERSISTENCE: Pest: Moderate NE:2 Short
** Mix with sufficient water to provide complete coverage.
Restricted entry interval (R.E.I.) is the number of hours (unless otherwise noted) from treatment until the treated area can be safely entered without protective clothing. Preharvest interval (P.H.I.) is the number of days from treatment to harvest. In some cases the REI exceeds the PHI. The longer of two intervals is the minimum time that must elapse before harvest.
* Permit required from county agricultural commissioner for purchase or use.
1 Rotate chemicals with a different mode-of-action Group number, and do not use products with the same mode-of-action Group number more than twice per season to help prevent the development of resistance. For example, the organophosphates have a Group number of 1B; chemicals with a 1B Group number should be alternated with chemicals that have a Group number other than 1B. Mode of action Group numbers are assigned by IRAC (Insecticide Resistance Action Committee). For additional information, see their Web site at
2 NE = natural enemies



[UC Peer Reviewed]

UC IPM Pest Management Guidelines: Cotton
UC ANR Publication 3444

Insects and Mites

  • L. D. Godfrey, Entomology, UC Davis
  • P. B. Goodell, UC IPM Program and Kearney Agricultural Research and Extension Center, Parlier
  • E. T. Natwick, UC Cooperative Extension - Desert Research and Extension Center, Imperial County
  • D.R. Haviland, UC Cooperative Extension, Kern County and UC IPM Program
  • V. M. Barlow, UC Cooperative Extension, Riverside County and UC IPM Program
Acknowledgment for contributions to Insects and Mites:
  • E. E. Grafton-Cardwell, Kearney Agricultural Research and Extension Center, Parlier
  • N. C. Toscano, Entomology, UC Riverside

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