The Olive Trees of Puglia: How Xylella Fastidiosa Redefined a Landscape

In southern Italy’s Puglia region, centuries-old olive trees once shaped both the economy and the identity of the land. But over the past decade, vast areas of these groves have turned silent and skeletal, the trees stripped of life by a microscopic invader: Xylella fastidiosa (Xf).

Xf was known to be endemic in the Americas, where it causes severe impacts for coffee and grape producers [1]. It probably spread to Europe for the first time in 2008, with olive growers noting symptoms in 2010, but Xf was not identified as the culprit until 2013 [2]. The spread of the bacterium to olives brought a new disease named Olive quick decline syndrome. Affected trees quickly see their branches dry out, their leaves yellow, and die [1].

Since the outbreak in Puglia began, yields have collapsed. Older olive groves—particularly those left without intensive management—have been hardest hit: they face yield losses estimated to be between 26 to 91% [2].

The economic costs have been staggering. Between 2016 and 2018 alone, olive yield losses in Puglia were equal to 10% of Italy’s olive production, costing nearly 390 million euros [2]. And beyond economics, the outbreak has had devastating cultural consequences: ‘Cutting down … olive trees means destroying the physical embodiment of [Apulians’] families and history. Here, the disease is killing irreplaceable trees, including those planted to mark the births of family members for generations. The harm to Apulian culture and society is perhaps beyond quantification.’ [3]

Containing Xf has proven difficult. It spreads via insects which feed on the tree’s sap. There is no cure once a tree is infected. Management depends on removing infected trees, controlling insect populations, and replanting with more tolerant olive varieties. But these measures are most effective if applied early, and the five-year delay in recognising the threat gave the disease a crucial head start in Puglia.

Today, the pathogen has now been detected in parts of France, Spain, and Portugal. Experts worry about the potential for this bacterium to devastate not only olive trees across the Mediterranean, but also almond, citrus and grape production [2]. Early warning systems and coordinated responses will be key to preventing this crisis from spreading further.