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Phylloxera In Napa Valley: Then and Now

An insect infestation born in America hitchhiked to Europe and nearly destroyed European vineyards in the 1800s. More than 100 years later, that same insect came devastatingly close to destroying the Napa wine industry before it even got off the ground. 

This parasitic insect, phylloxera, had a monumental effect on the U.S. wine industry. In the latter half of the 20th century, it infiltrated Napa’s vineyards and changed how viticulturists in America’s most prominent wine region approach agriculture. 

The Roots of Phylloxera: Where It Came From and How It Spread 

Phylloxera made its first appearance in California in the 1860s, after being born and bred on the East Coast of the United States.  

The pests likely “came with the westward expansion from the East,” says Dr. Andrew Walker, geneticist and endowed viticulture chair at University of California, Davis

It also made its way to Europe around the same time, via imported nursery or plant materials or other organic matter from the U.S.  

Phylloxera only affects vinifera varieties, not the American rootstock species Vitis rupestrisriparia or labrusca, which are mostly phylloxera resistant.  

As a result, the pest aggressively attacked Mission grape vines, a European Vitis vinifera variety that was popular throughout California at the time. The precipitous decline of these vinifera vines tipped winemakers and viticulturists off about a possible infestation. 

There’s an unspoken “Rule of 15” when it comes to phylloxera. It takes about 15 years before vineyard managers or winemakers detect phylloxera, since it burrows into vines and creates open wounds in the root system. Few pests actually kill vines, though. In the case of phylloxera, the wounds create the “entry point for soil-borne and pathogenic fungi,” says Walker. 

“That was hard for people to understand, since the vines were dying so quickly,” says Walker. 

Grape phylloxera (Daktulosphaira vitifoliae) on the vine leaves / Getty

In the 1870s, European rootstocks were brought to California to see which ones would work best in the region. Many tests and trials were done, and rootstock AxR1, a hybrid of Vitis vinifera and Vitis rupestris, seemed like the most appropriate choice because it was disease-resistant and easy to graft. But part of its parentage was still vinifera, so eventually those vines died off, as they were not immune to the pest’s damage. 

Napa’s Newest Phylloxera Infestation

Unfortunately, in the 1980s and ’90s, another phylloxera outbreak reached Napa. The first signs came in 1982, but winemakers and vineyard managers were in denial. The vines were still producing, they reasoned, and they also thought they had learned so much after the 19th century infestations.  

By 1992, nearly 1,600 acres of vines had to be removed entirely. 

“Its reproductive properties are incredible,” says Walker. “It has a 20-day egg cycle and can hatch up to 200 eggs during their short lives.” 

As with most everything in wine, climate is a factor, and in this case, it determines the insect’s reproductive capacity. In warmer climates like California, it can reproduce more quickly than in a cooler climate like, say, Washington, which had a recent phylloxera outbreak in 2019.  

(Washington’s vines were susceptible due to the fact that some are planted on their own rootstocks, rather than ones that are phylloxera-resistant).  

Around 70% of vines in Napa and Sonoma were planted to AxR1. About that same percentage of vines died in Napa. In total, between 50,000–70,000 acres were affected.  

The vines that survived were planted on St. George rootstock. It has high tolerance for viruses and is resistant to phylloxera.  

The loss of revenue due to the infestation was estimated at up to $1.25 billion, according to California Agriculture.  

Antique illustration: Grape phylloxera (Daktulosphaira vitifoliae) / Getty

What’s Being Done About Phylloxera Today? 

Unsurprisingly, phylloxera remains a threat to vineyards both in Napa and around the world. In California in particular, there’s a new strain that can live on leaves of the vine. If your eyes are good, you might be able to pick them out by their faint, golden glow.  

While sandy soils can limit damage caused by phylloxera, they can still exist in it, but when they move to finer-grained soils, they can cause much more damage. Once established, there’s practically no way to eliminate them. 

“They’re very easy to kill,” says Walker. “All you have to do is submerge them in water, and they die.” In Napa, however, “there were so many of them you weren’t making much of a dent.” 

Both arsenic and carbon bisulfide have been used to kill phylloxera in vineyards, but their use is restricted. Resistant root systems, like grafting vinifera vines onto American rootstock, are the best way to control them. And even then, those systems would only reach about 95% resistance. 

“Rootstocks solve the problem,” says Walker, “But we keep discovering new strains, while we figure out how to deal with the old ones.”  

The climate crisis also plays a role in determining how to fight future infestations in Napa, according to Walker. 

“People are suddenly realizing the a-ha moment of climate change, and we can address the climate problem without issue if we use new varieties,” says Walker. “The 10 or so kings and queens of varieties are not appropriate for hot climates [such as California], so we have to breed and grow new varieties.” 

Walker suggests winemakers and viticulturists use aerial photography to identify healthy and weak vines by their color and reflection from the air. 

Fortunately, there are many rootstock alternatives; in California, about 10 of these are generally used.  

Did Anything Good Come from the Phylloxera Infestation? 

This infestation catalyzed an industry-wide overhaul of viticultural practices. About 100 years after the initial French vineyard blight, there was a “much-needed revolution to shake up vineyards,” says Walker. Thought was given to the type of trellising, spacing, canopy management and even clonal selection that vineyards would use moving forward. 

“It gave people a chance to think about what could be done to optimize vineyard quality [in California],” says Walker.