The tree-killer is a bacterium called Xylella fastidiosa. Since 2013, it has killed millions of olive trees in Italy and is now threatening those in Spain and Greece. Together, these countries produce 95% of Europe’s olive oil.
A recent study projects that southern Europe, already crushed by the coronavirus pandemic, could lose at least $22 billion over the next 50 years, if Xylella spreads.
“There is no cure,” says Maria Saponari, a plant virologist at the Institute for Sustainable Plant Protection in Italy, “and the disease spreads quickly.”
Saponari compares Xylella to the coronavirus. Just as COVID-19 keeps oxygen from reaching our vital organs, she says, Xylella clogs the inside of olive trees so they can’t absorb water.
“On the outside, you see the leaves desiccate, you see the wood turn gray or brown, and the tree dies,” she says.
Saponari, who has studied Xylella for years, says the bacterium came to Italy from the Americas, where it ravaged citrus trees and vineyards. She says Italy likely imported ornamental coffee plants infected with Xylella. Because it flourishes in warm weather, “unfortunately it found a very suitable condition to establish here,” she says.
The pathogen is spread by sap-sucking insects like the spittlebug. Because there’s no cure, Saponari says farmers must focus on prevention, which includes keeping spittlebugs away from trees. One method involves weeding and tilling olive groves to kill insect larvae. Scientists have also suggested trying insect-repelling clays.