Olive trees infected by the Xylella bacterium must be felled to prevent the pathogen’s spread.Credit: : ROPI/Alamy

Thousands of olive growers and their supporters — including scientists — in the Italian region of Puglia have staged a demonstration calling for evidence-based action to combat a devastating olive-tree disease.

The protest, which took place in the small town of Monopoli on 13 January, is one of the first manifestations of increasing public support for science since the outbreak was identified. It follows several disputes over the destruction of trees in the region.

For the past five years, the southern region of Puglia has struggled to contain the spread of the bacterium Xylella fastidiosa — which causes incurable disease, called olive quick decline syndrome — in part, because of anti-science sentiment. The disease has run rampant in olive groves since it was identified in Puglia in 2013.

Tree felling

The outbreak is subject to European Union containment regulations. But efforts to control Xylella’s spread by destroying infected trees and the vegetation around them have been repeatedly hampered by environmentalists and farmers who want to prevent old, beloved olive trees from being cut down. The bacterium is spread by insects called spittlebugs.

Some activists have denied the scientific evidence that the bacterium causes the disease, and some local judges have imposed injunctions on the felling of particular infected trees.

Monopoli is at the northernmost edge of European Commission’s designated infected zone, and until recently the town had remained unaffected.

But in December, regular monitoring revealed an infected tree just beyond the infected-zone border. The zone must now be extended in a 10-kilometre radius around the tree.

On 12 January,﻿ a public prosecutor placed an injunction on the tree’s destruction. Three p﻿arliamentarians from the Five Star Movement — which is one of the two coalition partners in the Italian government — immediately claimed that the action was prompted by their own complaints that felling of the tree was unnecessary.

But two days later, the prosecutors said that they they had delayed destroying the tree because they instead wanted more time to investigate the possibility that the infection had been intentionally — and illegally — spread to the tree. The tree is 25 kilometres from any other infected tree, which is too far for normal insect-borne transmission, and surrounding vegetation doesn’t seem to be infected.

In the same week, Lello Ciampolillo — one of the three Five Star parliamentarians — declared on Facebook that he had lost his battle to save another infected olive tree in Cisternino, south of Monopoli in the infected zone. Ciampolillo said on his Facebook page that, last October, the owner of the tree and the patch of land it stood on ceded the area to Ciampolillo, who then declared it his parliamentary residence — which he claimed meant that no authority could enter it without his permission.

But on the evening of 14 January police protected plant-﻿health authorities as they destroyed the tree.