Worst Virus of Tomatoes

Be alert and scout regularly to catch yellow leaf curl disease

By Vicky Boyd, Editor

Photo courtesy of the Florida Department of Agriculture and Consumer Services Division of Plant Industry; www.bugwood.org.

Photo courtesy of the University of Georgia; www.bugwood.org

Photo courtesy of the Agricultural Research Service

A disease that at least one plant pathologist calls the “worst virus of tomatoes we know” continues to expand its reach in California since its initial discovery in 2007.

“I have seen what this virus does in certain parts of the world, and it’s scary,” says Bob Gilbertson, a University of California, Davis, plant pathology professor. “I want to emphasize that this has been in tropical areas that have whiteflies year-round.”

Although tomato yellow leaf curl virus still has only been found in a few scattered residential gardens and commercial tomato fields in Imperial and Riverside counties, it has prompted at least one county to consider plant movement restrictions.

Fresno County has proposed three options, two of which would require increased inspections of tomato transplants, says county agriculture commissioner Carol Hafner. They could cost the county between $40,000 and $43,000 annually, depending on the program.

The three proposals would replace a state exterior quarantine that the California Department of Food and Agriculture has proposed discontinuing because of a lack of money.

Should the state eliminate the exterior quarantine, individual counties could decide on what type of restrictions, if any, they would place on tomato transplant movement, she says. And transplant shippers could face a hodgepodge of county regulations.

Whiteflies help spread the virus

Tomato yellow leaf curl virus was first detected in California in a Brawley High School greenhouse in 2007 by University of California Cooperative Extension farm adviser Eric Natwick. The plants were started from seed.

Surveys have since detected it in a few scattered fields and gardens in Imperial and Riverside counties.

Ozgur Batuman, one of Gilbertson’s graduate students, detected one infected plant in a Merced County tomato field in 2008. He found it as part of his research on the more ubiquitous tomato spotted wilt virus.

But Gilbertson says he believes it was an isolated event and was a transplant moved in from elsewhere.

The disease also has been found in northern Mexico as well as Texas, Guatemala, Louisiana, Florida, Georgia, Texas and Arizona, Gilbertson says.

The virus is spread by Bemisia tabaci—the desert-resident greenhouse or silverleaf whitefly—not the sweet potato whitefly.

“What’s very bad is the whiteflies can acquire and transmit the virus very quickly—in minutes—and transmit it for the rest of their lives,” Gilbertson says.

The disease is not known to be seed transmitted. Whiteflies typically only fly a few miles, so most of the long-distance spread of the disease is through movement of infected plants, he says.

Plants infected with tomato yellow leaf curl virus are stunted and have a distinctive upright growth, sometimes called a bonsai symptom because they resemble a bonsai tree.

Leaves also are stunted, cupped or curled upright and turn a bright yellow with the veins remaining green.

If the plants are infected early in the season, they are “basically done for,” Gilbertson says. Later infections cause plant stunting and yield declines.

He encouraged growers to only use transplants produced instate that are apparently free of disease, since movement of infected plant material can help spread the virus.

Gilbertson also urged pest control advisers, consultants and growers who scout fields to report any suspicious plants to local Extension specialists or farm advisers so they can collect samples for testing.

Contact Vicky Boyd at (209) 571-0414 or vlboyd@att.net.