Resistance-Breaking TSWV is ‘Spreading in Scope’ in Sutter County

Brian GermanDisease, Tomatoes

Instances of the resistance-breaking strain of tomato spotted wilt virus (RB-TSWV) are increasing in Sutter County. Vegetable Crops Advisor with UC Cooperative Extension in Colusa, Sutter, and Yuba counties, Amber Vinchesi-Vahl said that the strain of the virus is “spreading in scope” in the area. RB-TSWV has been particularly troublesome for growers in Fresno County for a number of years. The Sw5 gene that has been used to protect tomatoes is no longer offering the same level of protection to this particular strain of the virus.


“We expected to see it up north eventually and last year we found it in south Sutter County last tomato season. Then this year we’re seeing it pop up more and more in northern Sutter County and I’ve heard of possibly some instances of it in Colusa County as well,” said Vinchesi-Vahl. “We’re not seeing any economic damage so far, but we know that it’s here and so we’re watching it and making sure that the growers and PCAs are controlling for thrips now that we can’t just rely on the varieties anymore.”

Monitoring for thrips and managing populations is a critical component of limiting the spread of RB-TSWV. Vinchesi-Vahl explained that growers should be aware that the third peak of adults should be occurring soon in the area, making it an appropriate time to spray for thrips. Confirmation and documentation of outbreaks are also important aspects of managing further RB-TSWV infections.

“Monitoring for the appearance of spotted wilt is really important and if you have planted a resistant variety and you’re seeing spotted wilt pop up more than just a few random plants, you can give me a call or bring me samples,” said Vinchesi-Vahl. “I can take them to the Gilbertson Lab at UC Davis where he can then test them to find out if it is that resistance breaking strain. We want to confirm that it is resistance breaking.”

Growers who may have TSWV in a resistant variety can reach Amber Vinchesi-Vahl at or 530-458-0575. Samples can also be dropped off for testing at the UCCE Colusa office or the UCCE Sutter-Yuba office.