All grapevines in the Classic Foundation Vineyard are individually tested each year 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 2025 testing has been completed, with GRBV detected in 1 vine and GLRaV-3 detected in one vine. This is the first occurrence of GRBV since 2019, and second year for GLRaV-3 detection. The positive vines were quickly removed and the surrounding vines will be re-tested to confirm their virus-negative status. Dormant vines distributed in winter 2026 will be tested a second time for GRBV and GLRaV-3 to verify they are virus free.
