Grower Voices - A Featured Guest Post by Ted Hall

Grower Voices shares perspectives from growers across Napa Valley. Some of the best insight on farming here comes from the people doing the work. This month, Ted Hall, who has walked Napa vineyard rows for about 35 years, looks at red blotch virus: how it spreads, what it costs, and why it may be the valley's most serious vineyard health threat since phylloxera. We're grateful he let us share it here. This article originally appeared on Ted's Substack on September 27, 2026. You can find more of his writing at Tell the Truth and Do the Right Thing. 

The Virus We Planted
Napa Valley's Next Phylloxera Crisis?

Ted Hall, Sep 27, 2026

I have walked vineyard rows in October for the better part of thirty-five years, reading the turn of the leaves the way every grower does: for color, for stress, for trouble. I could not tell you with certainty whether grapevine red blotch virus, a viral infection that quietly keeps an otherwise healthy-looking vine from ripening its fruit, is in a vineyard right now. That is not a comfortable thing for a grower to admit.

And not every red leaf means red blotch. Leafroll, nutrient deficiencies, trunk or root damage, and other stresses can produce similar symptoms.
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Red blotch can sit in a vine for two or three seasons before a single leaf shows reddish to reddish-purple blotches and the telltale redness in its veins, which means the honest answer for most growers in this valley is less a confident no than an unconfirmed not yet. Nobody would know without testing for it, and until recently, almost nobody did.

First recognized in Napa Valley in 2008, red blotch has since been confirmed in vineyards across the United States and internationally. Brix measures the sugar building up in a grape as it ripens, and the virus can cut that number by five or six degrees, while suppressing the anthocyanins that give red wine its color and altering the tannins and other phenolics that affect its structure. The mechanism is reasonably well understood: the virus disrupts the hormonal signals that trigger ripening, so the vine never receives the full instruction to finish the job it started in the spring.

A National Academies review commissioned by the California Department of Food and Agriculture in 2025 described grapevine red blotch and its sister disease, leafroll, as threats to a wine and wine grape sector that contributes $73 billion a year to the state’s economy, made harder to manage by how long it takes winemaking itself to reveal the damage.

Agricultural economists have modeled the lifetime cost of a heavily infected vineyard running into the tens of thousands of dollars an acre. That number is large enough to ask, carefully, whether this is the most consequential vineyard health threat Napa Valley has faced since the phylloxera crisis of the 1980s and 1990s forced growers across Napa and Sonoma to replant most of their vineyards at enormous cost.

Marc Fuchs, the Cornell plant pathologist who has spent over a decade tracking a single Cabernet Franc vineyard in Rutherford, watched its infection rate climb from 3.9% in 2014 to 36.4% in 2023. That vineyard sits in Rutherford, widely described as the center of Napa’s outbreak; nobody has done the valley-wide survey that would show how far the pattern actually extends beyond it.

He originally suspected red blotch was moving in from a nearby riparian corridor, the strip of wild vegetation that lines a creek or stream, which would mean many separate introductions, each carrying its own distinct genetic signature. The genetic evidence did not support that theory: the virus in his vineyard was too uniform for that many independent arrivals.

What he found instead were two distinct epidemics running in the same vineyard at the same time: a slow, randomly scattered spread of about 1% a year in one section, and a fast, radiating spread of about 6% a year in another, a difference he traces to how densely the vector, the insect that carries the virus from vine to vine, had already established itself in each part of the vineyard block.

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