Europe's Olive Trees Face a Pandemic of Their Own

CC BY 4.0. Wikimedia Commons

Nutrient-depleting bacteria are decimating olive groves throughout the Mediterranean, with devastating consequences.

Olive trees in Europe are facing a health crisis not unlike the one we humans are currently fighting. Since 2013, a deadly pathogen called Xylella fastidiosa, also known as olive leprosy, has been creeping through Mediterranean olive groves, transmitted by spittle bugs and other sap-sucking insects. It blocks a tree's ability to move nutrients water through its trunk, slows growth, withers the fruit, eventually killing the tree.

The BBC reports that Italy has seen a 60 percent decline in olive yields since the bacterium's discovery, with 17 percent of its olive-growing regions currently infected. One million trees have already died and economic losses could be as high as €5 billion over the next 50 years unless Italy manages to halt its spread. In Spain, it could cost as much as €17 billion, and in Greece just under €2 billion.

New research has come out this month about the severity of the disease and measures that should be taken by olive growers and governments of affected regions in order to minimize damage. Published in the journal Proceedings of the National Academy of Sciences (PNAS), researchers from Wageningen University in the Netherlands modelled various scenarios, from the worst case – if all olive production ceased due to tree deaths – to a better-case projection – if all trees were replaced with resistant varieties.

The researchers are concerned about the fact that, combined, Spain, Italy, and Greece account for 95 percent of Europe's olive oil production, and all of these places have optimal climates for the bacteria to thrive. (It has also been found in France and Portugal.) The Guardian reports, "Between 85 percent and 99 percent of all producing areas susceptible. The spread of the disease is currently 5km a year, but could be reduced to a little over 1km a year with appropriate measures."

Those measures, however, are not pleasant. They require the destruction of infected trees, which is not only an enormous undertaking, but also psychologically taxing on growers who may have inherited their families' olive groves from hundreds of years ago. The researchers said they were unable to calculate this cultural heritage, saying it's impossible to "put an economic number on the loss of something like this." Seemingly healthy trees must be destroyed sometimes, too, because they could be vectors for the bacteria. The implementation of a 'cordon sanitaire', or boundary that divides infected areas from healthy ones, was found to result in "great societal unrest in the affected region," presumably because people were distressed by the loss of the trees.

Some scientists and growers are investigating solutions closer to the trees, such as "mechanical intervention to remove weeds in spring, [which] is one of the most efficacious applications to reduce the populations of the insect," as well as "insect repelling clays, vegetative barriers and genetic analysis to determine why some plants are more susceptible to the infection than others."

Unless the infection is brought under control, global consumers could find the cost of olive oil increasing as a result of shortages. In the meantime: "Seeking resistant cultivars or immune species is one of the most promising, and environmentally sustainable, long-term control strategies to which the European scientific community is devoting relevant research efforts."

And, as most studies conclude, more research is needed.