Recent testing of material distributed from the Foundation Plant Services Classic Foundation Vineyard at the University of California, Davis, detected zero cases of grapevine red blotch and grapevine leafroll associated virus-3 infections, after one positive result during annual testing last fall.

“At this time there is no concern but we cannot get complacent,” Director Maher Al Rwahnih said of the results. “We will continue testing all individual vines every year and reconfirm that orders of Foundation Plant Services source vines are negative.” 

Foundation Plant Services, or FPS, annually tests grapevines at its Classic Foundation Vineyard for grapevine red blotch virus, grapevine leafroll associated virus-3 and other economically important viruses. In October 2024, one vine out of 4,881 tested positive for grapevine leafroll associated virus-3, an infection last seen in the vineyard in 1994. 

That vine was removed and surrounding vines were re-tested to ensure they were negative as well. The infected vine was also inspected for mealybug, which can transmit the virus, and none were found. 

FPS recently conducted additional tests on all plant material distributed this year — and those vines that had been near the infected vine last year — and did not detect any virus. Monitoring of the surrounding vines will continue through the summer. 

A source for industry

FPS provides high-quality, virus-tested grapevine material to the grapevine industry in the United States and serves as the primary source for plant materials sent to nurseries under the California Department of Agriculture’s Grapevine Registration and Certification Program. 

The Classic Vineyard is home to more than 2,450 wine, table, raisin and rootstock grape selections. In 2024, Foundation Plant Services opened a new greenhouse to protect and propagate those plants in an environment safe from insects. 

The grapevine leafroll associated virus-3 detection underscores the need to safeguard the vineyard’s clean grapevine collection, Al Rwahnih said. Foundation Plant Services is fundraising for a new screenhouse to further protect and make room for up to 2,000 more grape selections. The estimated cost is $3.6 million. 

“Leafroll virus-3 is a severe virus,” Al Rwahnih said. “There is zero tolerance for it, red blotch or other economically important viruses. We cannot have them present.”