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Seeking answers to Tomato Spotted Wilt Virus

New UCCE Fresno County farm advisor and plant pathologist Tom Turini has moved from Imperial County to the West Side of the San Joaquin Valley, with an early focus on helping processing tomato growers solve the tomato spotted wilt virus (TSWV) problem in their fields.

The thrips vectored virus struck many SJV processing tomato fields last year, in some cases decimating entire blocks of tomatoes. The virus was confirmed in several Central valley locations, but seemed especially severe in the area from Huron south.

Turini has joined a cooperative UCCE partnership to learn more about where the virus comes from, how it is transmitted, how to control the vector, and ways to minimize the impact of the virus on processing tomato crops once fields become infected.

There are some 900 known host plants for TSWV, including malva, some thistles and other weeds, providing a potential reservoir for infection in tomato fields. The disease is vectored from one plant to another by thrips.

Turini has been studying host plants, along with the biology of the virus, thrips vector and the potential use of plant activators to help improve understanding and management of the virus.

Plant activators, such as Messenger or Actigard, have shown promise for increasing yields in plants infected by similar viruses in other areas, Turini said. Trials on northwest onions, for instance, showed an increase in bulb size in the presence of similar viruses through the application of plant activators.

Monitoring in the San Joaquin Valley started in February, using highly susceptible indicator plants in the greenhouse and field, along with sticky cards to detect presence of the virus or thrips in the field. By mid-May the virus already had been detected on the southern part of the West Side, though incidence was still relatively low, Turini said.

Surveying has become a critical component in the overall project to help researchers increase awareness about where the virus is and how it is transmitted.

Tomato spotted wilt virus symptoms initially appear as bronzing at the early stages on younger leaves that develop into dead spots. Later, infected plants appear stunted, followed by severe leaf death and failure to produce fruit. Fruit is sometimes distorted at the early stage and as it starts to color, yellow circular spots begin to appear.

“If PCAs believe they have it in the field it would be a great service if they could contact us directly,” Turini said. “We need to get a clearer sense of what’s going on out there and PCAs are an excellent resource for projects like this.”

He encourages growers and PCAs to call him at (559)-375-3147 to report suspected virus so the incidence can be confirmed through quick tests in the field or lab.

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