Pest alert for South American bean thrips in alfalfa in Southern California

Charlie Summers, University of California entomologist, has found South American bean thrips (Caliothrips phaseoli) on alfalfa at the University of California Kearney Field Station near Reedley, Calif.

This insect occurs in the desert areas of Southern California (Imperial and Palo Verde valleys). The adult thrips are black with white bands on the wings. Nymphs are yellow with pinkish or reddish markings.

From a distance, affected plants appear severely moisture stressed. Upon closer evaluation, many terminals are blasted and appear dead. Large areas of the epidermis are stripped off by this insect leaving large white areas on the leaflets. Leaflets and other plant parts are covered with black specks of feces.

Feeding by the flower thrips only results in crinkled leaves and treatment is only rarely considered necessary. Feeding injury by this bean thrip, however, can be severe enough that treatment may be necessary, although thresholds have not been established and only rarely in Southern California have treatments been applied.

Since Summer’s report, two farm advisors in Kern County report having seen damage from this insect.

If growers observe fields with this insect or injury that resembles what’s noted above, send an e-mail to [email protected] or call (559) 685-3309, ext. 214.

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