By TIM HEARDEN
SACRAMENTO -- As their harvest draws near, tomato growers in California's San Joaquin Valley are grappling with a plant-shriveling virus that is causing significant damage in some areas.
The beet curly top virus, which is carried from plant to plant by the beet leafhopper and stunts growth, has been reported in tomato fields in Fresno, Kern and Merced counties with some significant damage in Fresno County, according to the USDA's National Agricultural Statistics Service office here.
Acting Fresno County Agricultural Commissioner Les Wright said a grower told him some of his neighbors had suffered 50 percent or greater losses and that they were replanting. He said curly top virus tends to be worse in dry years with warm winters, when the leafhopper's winter die-off is decreased and more of the insects come down to the valley looking for green plants.
"In drought years, it does seem to be a bigger problem for us," Wright said.
The virus can affect a wide range of crops including sugarbeets, dry beans, potatoes and others, explains the University of California's Statewide Integrated Pest Management Program. In tomatoes, plants turn yellow to bronze in color with purple-tinged leaves, become stiff and soon die. Green fruit turns red, regardless of age, according to IPM.
Infected plants are often widely scattered in a field, although margins are especially vulnerable because leafhoppers like to feed on plants that border bare soil areas, IPM explains. In some years the virus has caused almost complete crop loss in individual fields near the foothills, according to the agency.
The virus comes as California's tomato processors anticipate contracts for 13.1 million tons of processing tomatoes for 2013, a 4.5 percent increase from the final contracted production total in 2012, according to NASS. The May contracted acreage of 259,000 was 2,000 below the agency's predictions in January but 1,000 above last year's acreage.
The tomato harvest typically runs from early July to mid-October, although cool and wet springs in some recent years have frustrated farmers' efforts to get a crop in the ground and caused them to spend more money than anticipated on fumigants.
A 13.1 million ton crop would be the state's second largest in history, falling just short of the 2009 record crop of 13.2 million tons. However, the due date for processors to submit their intentions was May 14, which was before some fields infected with the curly top virus showed visible signs of damage, noted the California Tomato Growers Association.
As such, replanting was an option in only a few fields, the CTGA reported in a bulletin to growers. While the growers' group said it's difficult to predict the reduction the virus may cause in the total tonnage, it is apparent that many fields are infected and some have significant plant loss.
The state control program is limited to working on roadsides and non-crop areas, the CTGA noted. The group advised growers to identify nearby fields that are hosts, determine the level of risk and work with their neighbors to minimize the ongoing movement.
Among measures that growers can take include shading plants, as the insect has shown a preference to feed in areas where sunlight is abundant, and using some type of closure such as a row cover made of a synthetic material, according to a Utah State University Extension fact sheet. Double-planting of tomatoes is also an option that could ensure some yield, according to the university.
California Tomato Growers Association: http://www.ctga.org
University of California Statewide Integrated Pest Management Program: http://www.ipm.ucdavis.edu
Utah State University fact sheet on curly top: http://extension.usu.edu/files/publications/factsheet/curly-top-tomato08.pdf