Voracious Strain of Whitefly Found in San Joaquin Valley

The voracious strain B whitefly has moved into the San Joaquin Valley, the most fertile and productive agricultural area in the state. If the whiteflies stay there over the winter they could pose a serious threat to millions of dollars worth of crops next spring and summer.

Tests confirmed that whiteflies found in August on weeds in Fresno County are strain B--the type of whitefly that has been devouring crops in California’s Imperial Valley and other areas throughout the Southwest, a team of researchers from the U.S. Department of Agriculture said Thursday.

The confirmation marks the most northerly discovery of strain B whiteflies outdoors. Last year and earlier this season the pests were found in greenhouses in the San Joaquin Valley, and outdoors in Kern County in the southern part of the valley.

The question facing scientists, growers and thousands of laborers who depend on San Joaquin Valley agriculture for their livelihoods is how successful the whiteflies will be in surviving a cool, wet winter.

“If they are over-wintering, instead of being blown in from the desert regions, it could be a serious problem in the San Joaquin Valley,” scientist James Duffus said. Duffus, a whitefly expert, heads the team of researchers in the USDA’s Agricultural Research Station in Salinas that found the strain B whiteflies.

Duffus predicted that even if it is not this year, strain B will soon be able to spend winters in the valley; it has already shown great adaptability and is prolific. The more flies there are, the better the chance they will survive, adapt and wreak havoc, he said.

Strain B, previously called the poinsettia strain of sweet potato whitefly, damaged crops in Imperial County last winter, causing an estimated $130 million in losses. The fly attaches itself to the leaves of plants and sucks out the nutrients.

Throughout the Southwest’s desert growing regions, the whitefly has come back this year in large numbers--but U.S. growers were prepared and are predicting that damage will be limited. In Imperial County, farmers have not planted some crops that the pest finds tasty, have harvested others early and have implemented strict weed abatement programs to minimize feeding areas.

Without precautions, however, the lucrative agricultural economy of the San Joaquin Valley could be laid waste by the hungry little bugs, Imperial County experts warned.

So far, there are few--if any--programs in place in San Joaquin Valley to mitigate losses.

Growers in the valley “think they are in a safe position because they are north of the Tehachapis (mountain range) and they have a colder winter,” said John Pierre Menveille, a grower and chairman of the Imperial County Whitefly Management Committee. “But if they saw firsthand some of the devastation we had here last year they’d be thinking twice about what they are doing.”

David Ritter, coordinator of the whitefly committee for the county’s agricultural commission, said San Joaquin Valley agricultural officials have not asked for help. “When it came in here we didn’t know we had it and all of a sudden we were in the middle of (an infestation) and running around trying to do something. . . . Maybe they should work on it now, being forewarned,” Ritter said.

The whitefly discoveries come as no surprise to agriculture officials in the San Joaquin Valley, an eight-county region that last year produced more than half of the state’s $18 billion worth of agricultural products. “We figured it was a matter of time,” said Norman J. Smith, an entomologist with the Fresno County Department of Agriculture. Now, he said, “it is here without a doubt.”

But the prevailing opinion is that the whitefly will not survive the winter, Smith said, and “we’re keeping our fingers crossed.”

Smith said it would be difficult to persuade growers to forgo planting host crops such as lettuce. “When you’ve got a $94-million crop, to tell the farmers not to plant it is not going to work.”