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USDA Scientist Says Dangerous Pest Now in Crop-Rich San Joaquin Valley

September 17, 1992

FRESNO, Calif. (AP) _ Whiteflies that devastated desert crops have invaded the San Joaquin Valley, the heart of California’s diverse agricultural bounty, a government scientist said Thursday.

The pests, commonly called poinsettia whiteflies, have been found on weeds and cotton plants in the nation’s three richest farming counties - Kern, Tulare and Fresno, said Jim Duffus of the United States Department of Agriculture.

The whiteflies have caused minor damage in Kern County cotton and no major damage is expected this season because the crop will be harvested within a few months, Duffus said.

Scientists don’t yet know whether the poinsettia strain can live through the winter in the 200-mile-long San Joaquin Valley, where nighttime temperatures often fall below freezing.

The winter climate is much colder than the Imperial Valley’s, 200 miles to the southeast, where the pests have caused $130 million in crop losses.

″We do have a distinct summer and winter here in contrast to Southern California,″ said Hodge Black, an entomologist and University of California farm adviser for Kern County.

However, a lot of alfalfa, a common host for whiteflies, grows year-round in the San Joaquin Valley. ″We’re playing a waiting game - hoping for the best but bracing and preparing ourselves for the worst,″ Hodge said.

Duffus said samples his technicians took from San Joaquin Valley fields prove the poinsettia strain is present, but the samples weren’t large enough to show how large the infestation is at present.

The San Joaquin Valley between Los Angeles and San Francisco grows more than 200 crops, mainly fruits, nuts and vegetables. The region’s gross agricultural production totaled $10.2 billion last year, 57 percent of California’s $17.9 billion total.

The poinsettia whiteflies, or strain B, can cause more damage to more types of crops than the ancestor from which it mutated, the cotton whitefly, or strain A, Duffus said in a telephone interview.

″The B-type also produces eight to 10 times as many nymphs (offspring) as the A-type,″ he added. ″And it can reproduce almost 30 percent faster.″

Whitefly nymphs secrete what’s known as sooty mold, a sticky sugarlike substance that disfigures leaves. If sooty mold gets on cotton bolls, the lint can become sticky and less valuable.

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