Beet Curly Top Virus is a viral disease of tomatoes vectored by the sugarbeet leafhopper. In California, leafhoppers overwinter in the foothills and in the spring they migrate down into tomato fields. Since 1943 the California Department of Agriculture has conducted a spray program targeting the leafhopper in the foothills. This spray program has prevented massive losses in tomato fields. However, in recent years organic farming operations in the foothills have been exempt from the spray program. As a result, large populations of leafhoppers have migrated from the unsprayed organic fields into tomato fields with disastrous results.
“Had California’s 2013 tomato crop not been hit so hard by the Beet curly top virus (BCTV) it could have been a banner year for growers.
Bob Gilbertson, plant pathologist with the University of California, Davis, estimates last year’s tomato crop was reduced by about a million tons because of BCTV, which is vectored by the Beet leafhopper.
Tomato plants with BCTV become stunted and develop curled leaves. Upon closer inspection of the undersides of tomato leaves the veins appear swollen and they turn purple, Gilbertson said. Plants also turn a dull green-to-yellow and the fruit is small and tends to ripen prematurely.
Disease transmission begins early in the season as leafhoppers migrate from the foothills to the agricultural valleys, but can also happen during the growing season.
Adult leafhoppers tend to overwinter in the foothills. In the spring the females lay eggs on the green plants in the foothills and acquire the virus during feeding. As new leafhoppers become adults they then migrate to the valley.
The California Department of Food and Agriculture has a curly top spray program where the state sprays the foothills for the Beet leafhopper.
Tomatoes with curly top symptoms began showing up in late March of last year. Losses were the highest in Fresno, Kern and Kings Counties. Yield losses appeared far beyond the western foothills, and even into San Joaquin County.
Why was it so bad?
Gilbertson suspects a combination of favorable conditions for the leafhopper and hosts for the virus in the foothills.
There are limitations on the spray program, which could have helped leafhopper populations thrive.
“The spray program is being constrained now by certain farmers who want to do organic production in the foothills,” he said.”
Author: Fitchette, T.
Title: Virus slams 2013 California tomato yields.
Source: Western Farm Press. 2014-02-12. Available: http://westernfarmpress.com/vegetables/virus-slams-2013-california-tomato-yields?page=4