Warmer temperatures put European vineyards on alert for Pierce’s disease.

European wine regions are increasing their watch for Pierce’s disease as warmer temperatures raise concern that the bacterial threat could move further across the continent and put vineyards at greater risk.

The disease is caused by Xylella fastidiosa, a bacterium that attacks many plant species and can trigger different illnesses depending on the host. In grapevines, some strains cause Pierce’s disease by blocking the plant’s water transport system. Once that happens, vines can weaken quickly and die within a few years. Growers often see scorched-looking leaves, stunted growth and signs of dehydration as the disease advances.

The concern in Europe remains limited but real. Pierce’s disease is being contained in Portugal and on Mallorca, the Balearic island in Spain, according to the source report. Cases on the European mainland are still considered low, in part because cooler average temperatures have historically helped suppress the bacterium. But that climate advantage may weaken as temperatures rise.

The warning is shaped in part by what happened in California, where Pierce’s disease has long been a major concern in warmer growing areas. The disease was first identified near Anaheim in 1892 by Newton B. Pierce, the scientist whose name it carries. More than a century later, a new wave of damage hit Southern California after the glassy-winged sharpshooter, an insect that carries the bacterium, helped spread infections through vineyards.

In the late 1990s, Temecula Valley was enjoying strong wine sales and rapid optimism. That momentum was disrupted when growers began seeing vines decline for reasons they did not yet understand. Blocks of Barbera, Chardonnay and Riesling were badly affected. University researchers and the U.S. Department of Agriculture later identified Xylella fastidiosa as the cause. In the years that followed, the disease reshaped vineyards in Southern California and cost growers more than $48 million a year, according to the report.

That experience is now being studied in Europe as a warning of what can happen when the bacterium reaches a favorable climate and an efficient insect vector. California’s lesson was not only about losses. It also showed the importance of early detection, coordinated research and fast action when infected vines are found.

Xylella fastidiosa first drew major attention in Europe after it was detected in olive trees in Italy in 2013. Pierce’s disease was later found in grapevines on Mallorca in 2016. The first known detection in a grapevine on continental Europe came in 2023, when authorities found a single infected vine in Portugal. The case was managed quickly, but it intensified questions about whether the disease could spread into other mainland wine regions if temperatures keep rising and conditions become more favorable.

The economic stakes are high. Europe is facing an estimated potential damage bill of €5.5 billion if Pierce’s disease spreads more broadly, the report said. That risk matters directly to the beverage sector because vineyards are the base of a large share of the continent’s wine production. Any wider outbreak could increase costs for growers, reduce grape supply and put added pressure on wineries already dealing with climate stress, labor costs and volatile harvests. The impact would not be limited to vineyard owners. It could also reach cooperatives, exporters, tourism businesses and regions whose local economies depend heavily on wine.

The bacterium’s sensitivity to temperature is central to the current concern. Cold conditions can limit or suppress Xylella fastidiosa, while hotter conditions speed damage in infected vines. That pattern helps explain why Pierce’s disease remained largely confined to warmer wine regions for much of its history. It also explains why climate change has turned what was once seen as a regional problem into a broader agricultural threat.

For European producers, the question is no longer whether Pierce’s disease exists in the region, but whether today’s isolated cases can remain isolated. The disease has not yet taken hold across continental wine country, and the known grapevine detections remain limited. Even so, the appearance of the bacterium in olives, then in vines on Mallorca, and later in mainland Portugal has created a timeline that many growers are treating as an early warning.

That is why researchers and winegrowers in Europe are paying close attention to the methods developed in California, where officials and producers spent years learning how to monitor infections, contain vectors and manage losses. The aim is to avoid a repeat of the disruption that struck Southern California’s vineyards when the disease spread before the industry fully understood what it was facing.

For now, Europe’s response is focused on vigilance and containment. The threat is still uneven and local rather than widespread. But the combination of rising temperatures, the presence of Xylella fastidiosa in parts of Europe and the memory of California’s losses has made Pierce’s disease one of the clearest examples of how plant health, climate pressure and the future of wine production are becoming more closely linked.