In the late 1990s, Temecula Valley was riding a wave of strong sales and even stronger optimism. But a persistent and then unknown disease would bring the region, along with most of California’s winegrowing industry, to a halt.
J.D. Harkey, the director of operations at Drake Enterprises, recalls the scene: “These vines looked like they were torched—stunted growth, yellowing of the leaves, burned edges of the leaves—and nobody had any idea what it was. Large blocks of Barbera, Chardonnay, and Riesling were just dying.”
Over time, university researchers, alongside the USDA, identified the cause: Xylella fastidiosa, a bacterium that causes Pierce’s disease carried, in this case, by the glassy-winged sharpshooter.
In the years that followed, the disease would reshape Southern California vineyards, costing growers more than $48 million a year. More significantly, it would offer an ongoing lesson in how to fight a pathogen that seemed untouchable.
Understanding Pierce’s Disease
Xylella fastidiosa is a bacterium that attacks many plant species and can cause different diseases depending on the host. In grapevines, certain strains can cause Pierce’s disease by blocking their water transport, causing them to die within a matter of years. Vines appear torched or burned; it’s because the plants can no longer absorb water, causing them to die of dehydration.
This particular disease, discovered by Newton B. Pierce, first surfaced near Anaheim, California, in 1892. Cold climates can suppress the bacterium, but hot climates only accelerate the damage. This temperature sensitivity explains why the disease has remained confined to warmer wine regions for over a century, and why a warming climate means new regions are now facing threats from Pierce’s disease.
Cases of Pierce’s disease in continental Europe are still considered low, particularly because of the average lower temperatures, but Pierce’s disease is actively being contained in Portugal, as well as on the Balearic island of Mallorca in Spain. With an estimated potential economic damage of €5.5 billion, Europe is keeping a watchful eye on the disease, and California winegrowers and researchers are sharing what they’ve learned to help Europe avoid the same mistakes.
The current landscape of Pierce’s Disease in Europe
Xylella fastidiosa was first detected in Europe on olive trees in Italy in 2013, and later, Pierce’s disease was found in grapevines on the island of Mallorca in 2016. But it wasn’t detected on grapevines in continental Europe until 2023, when a single infected grapevine was detected in Portugal. While swiftly managed, that case raised questions over the possibility of spreading to other parts of mainland Europe.
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