All grapevines in the Classic Foundation Vineyard are individually tested each fall to screen for presence of grapevine red blotch virus (GRBV) and grapevine leafroll associated virus-3 (GLRaV-3). Both viruses are prohibited by the CDFA Grapevine Registration & Certification Program and are of great concern because they are vectored by insects and can quickly spread in a vineyard.
GRBV was first discovered in both the Russell Ranch and Classic vineyards in 2017. While the virus spread through Russell Ranch, resulting in its abandonment as a source of clean material, the GRBV infection rate at the Classic Foundation Vineyard has remained relatively low (0% to 0.02%).
The 2024 fall testing has been completed, with GRBV detected in 0 vines, and GLRaV-3 detected in one vine. GLRaV-3 infection had not been detected in the Classic Foundation Vineyard since 1994. The GLRaV-3 positive vine was quickly removed, and the surrounding vines re-tested to confirm their virus-negative status. The vine was asymptomatic, and infection was only discovered because of RT-qPCR testing. The infected vine was carefully inspected for mealybug (insect vector of GLRaV-3), and none were found. Infection occurred despite FPS’s strict program for insect pest management, including both systemic and contact insecticides, but so far appears limited.
Dormant vines distributed in winter 2025 will be tested a second time for GRBV and GLRaV-3 to verify they are virus free.
We hope the GLRaV-3 detection at Classic is not a precursor of wider infection in the vineyard but have been preparing for a reality where clean foundation vines can no longer be maintained outdoors. This 2024 GLRaV-3 detection underscores the urgent need to protect material in the indoor collection. The first greenhouse to protect the foundation collection was completed in March 2024, and now houses potted vines representing a portion of the Classic Foundation Vineyard. Fortunately, material from the infected selection was collected and propagated in January 2024, before infection, and the propagates have been confirmed GLRaV-3 negative. The greenhouse collection is an important vault of grapevine material secured against the threat of insect-vectored pathogens.
FPS is working closely with the UC Davis College of Agriculture and Environmental Sciences Dean's Office and industry to plan and fund a phase 2 screenhouse. The additional screenhouse will double the indoor collection capacity so each vine can be maintained at a large enough size to produce quantities of budwood useful to the industry and the collection can continue to expand.
