Tomato-Killing Virus Makes its Appearance in California

By: Laura Kurtzman AP
By: Laura Kurtzman AP

An insect-borne virus that has killed tomato plants across Central America, Florida and Georgia has been detected in California for the first time.

The virus, known as tomato yellow leaf curl, devastated crops in the Dominican Republican and in Mexico, forcing those countries to curtail the growing season to contain the spread of the disease.

Tomatoes are California's eighth largest crop. The state supplies the vast majority of the nation's processed tomatoes - 95 percent, according to the California Tomato Growers Association.

"Where this virus is present, it will absolutely kill the tomatoes," said Ross Siragusa, president of the association, which represents farmers who supply the state's $2 billion a year processed tomato industry. "It's a very difficult disease to fight."

California has some natural advantages in stopping the disease from spreading that other locales lack.

The cold, wet winters in the Central Valley, where most tomatoes are grown, act as barriers to the bemisia white flies that carry the disease. The flies are native to Imperial, Riverside and San Diego counties in the southern part of the state, but not to any counties in the Central Valley.

"We're cautiously optimistic that those conditions are going to be very unfavorable to establishment of the virus," said Robert Gilbertson, a plant pathologist at the University of California, Davis.

The diseased plants were found in March at a greenhouse in Brawley, which is near the border with Mexico. Experts do not know how the virus spread there. It could have been brought by tomato transplants from Mexico or Texas. Or the virus could have been carried by bemisia flies.

The virus causes tomato plants to become stunted and grow abnormally upright. Flowers usually fall off before the fruit sets. And leaves are small and crumpled with an upward curl. They also turn yellow.

Experts say growers or backyard gardeners who detect the disease
should destroy the infected plants and look for the flies. If bemesia flies are present, the disease is likely to be spreading fast, and the entire field may have to be destroyed and treated with insecticide. Nearby weeds also can carry the virus and may have to be sprayed.

In Florida, where the virus has become well established, Gilbertson said growers have had to make heavy use of pesticides and have planted tomato varieties that are more resistant to the disease. But flies may become resistant to the pesticides over time.

Siragusa said his group has alerted growers, greenhouses and seed companies that the virus has spread to California. But, he said, controlling the virus will be especially hard because so many tomatoes are grown in backyards.

(Copyright 2007 by The Associated Press. All Rights Reserved.)


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