SALENTO, Italy—There is only one certainty in what has fast become a Dantesque drama to save world-renowned olive groves in Puglia from the deadly Xylella fastidiosa bacterium: olive trees, the very symbol of this southern Italian region, are dying en masse. Hundreds of acres of once-vibrant, postcard-perfect groves that have prospered for centuries are now cemeteries where twisted, dead tree trunks protrude like arboreal zombies from fertile soil in which grass and flowers easily grow.

Almost every other aspect of the drama, especially the science of how the bacterium spreads and how to stop it, is far less clear. No one even knows how many trees have perished so far, although reports by Italy’s farm cooperative Coldiretti estimate that more than one million of Puglia’s 60 million olive trees are infected by the bacterium, either dying on their own or cut down and burned by authorities, under pressure to do something from national and European leaders who fear the bacteria could wipe out olive groves across the continent and infect almond and cherry trees, too. As I stand among the sawed-off stumps and charred remains of a small grove here, officials have just painted more of the ancient tree trunks with red X marks to signify eventual destruction. Angry owners protest defiantly, calling the men with chainsaws assassins. Activists shout insults at agronomists inspecting the groves.

But no one can tell me exactly how this bacterium sickens the trees, how it moves from tree to tree or whether burning can ever work unless it destroys the entire industry. Puglia produces more than 40 percent of Italy’s olive oil, and the oil is considered among the world’s finest. The outbreak could cost the region more than $225 million in olive oil production losses this year alone, and could threaten olive trees across Italy and all of Europe, substantially raising the price of oil worldwide. The stunning, centuries-old trees are more than agricultural champions, too; they are cultural monuments that are as vital to the “heel” region of Italy’s “boot” as its conical-roofed stone trullo houses and its many castles.

Nor can anyone say with certainty whether all of those dead trees actually succumbed to X. fastidiosa. Although current wisdom, based on random samples, holds that they did die from the bacterium, hardly a tiny fraction of the dead trees has been tested. Yet like conducting autopsies in a war zone, officials seem to have little impetus to confirm what is assumed as fact.

tree with red X
A red X marks trees destined to be destroyed. Credit: Pier Paolo Cito

Less certain still is just how the deadly bacterium was introduced to the area. The most likely explanation, supported by the scientific community, is that it was inadvertently brought in with a shipment of ornamental plants from Costa Rica, where the same strain of bacterium has been well documented. But local people here have their own theories, which range from the intentional killing of the trees by everyone from British land developers who want to clear the land to build fancy resorts and golf courses to the so-called ecomafia that apparently intends to repurpose the land as a toxic chemical dump.

Residents tell tales of dark-colored Mercedes and Jaguar cars apparently dumping chemicals on tree roots. Others whisper that the U.S. biotech firm Monsanto released a genetically modified strain of the bacterium they bought from a Brazilian company called Allelyx so it could sweep in with a cure. Still others claim that officials who support a proposal to build the Trans Adriatic Pipeline from Turkey to Europe via Puglia need to clear the land now occupied by olive groves to secure the lucrative deal.

Putting aside for the moment just how the bacterium came to Puglia, a far more pressing issue is how to keep it from spreading up the Italian boot and into Europe. Xylella is carried by infectious, meadow spittle bugs that feed on the trees’ xylem—tissue that supports the plant and conducts water. The bugs harbor the bacterium in their throats, moving among the trees, injecting the bacterium when they puncture trees to feed. As I look at several of the dead bugs floating in ammonia in petri dishes at the National Research Council of Italy (CNR) laboratory in Bari, it seems unfathomable that such small creatures could wreak such havoc. But even the bugs’ life is unclear; some scientists tell me the bugs can only travel 100 meters but others say the insects can travel for kilometers. That complicates the leading theory that in order to prevent the bugs from spreading the deadly bacterium, the infected trees must be destroyed before they die on their own, no matter how old or culturally important they are to the region.

Alarmed, the European Union has mandated the creation of a buffer zone just north of the Pugliese town of Lecce, essentially writing off everything south of a line that extends between the Ionian and Adriatic seas as a dead zone. Testing is more vigorous in and above the buffer zone. Infected trees are marked with a red X and destroyed. Eventually, every tree within 100 meters of any infected tree will also be cut down. Farmers are understandably defiant. “There is no such thing as Xylella,” says Pasquale Spina, a farmer whose trees are in the buffer zone. As he talks to me he stands next to the sawed off remains of an ancient tree that tested positive for the bacterium, stroking the new growth sprouting from the top of the supposedly infected, dead stump (see the video below). “Does this tree look sick to you?” he asks? “Xylella only exists in the head!”

One of the heads he is referring to is that of Donato Boscia, a virologist who is the research director of the CNR’s Institute for Sustainable Plant Protection. He found the first confirmed case of X. fastiodosa in his father-in-law’s olive grove in 2013 when he was there with his wife’s family. “I knew right away we had something big here,” he told Scientific American in his greenhouse laboratory in Bari. Boscia, whose cell phone shows an olive tree from his father-in-law’s grove as its screen saver, is leading an epic battle against a mountain of bureaucracy and funding cuts to institute an open-air research center to study the disease and eventually find a way to stop it. Although he advocates tree cutting and burning, he also knows it is the equivalent of taking an aspirin to fight cancer. “Eradication is not a utopia,” he says. “We need to work on containment. We have to adopt good practices to live with Xylella because stopping it is not going to be easy.”

Boscia is also at the center of a criminal investigation being conducted by the regional court in Lecce into the potential culpability of scientists for either introducing the virus or succumbing to pressure or financial persuasion not to stop it. Boscia is unfazed—at least on the surface— shrugging off the allegations and vowing to continue to find enough proof to implement what is necessary to stop the bacteria. “We can’t get distracted,” he says. “To beat this we need to stay focused.”

But science does not always play well in a land where adherence to tradition is rivaled only by suspicion of authority. Boscia’s job in convincing the public that the E.U. plan is the best they’ve got is complicated by the lack of proper funding and the blatant lack of an infrastructure that makes transparency nearly impossible. If an olive grower notices a suspect patch of drying leaves on a tree limb, he is more likely to cut the tree down and burn it himself than to wait for authorities to potentially come in and destroy the entire grove. There is not a single publicized help line or outreach program in the area to guide olive growers through the crisis, which means they have to take care of it on their own.

The delay in establishing an aggressive research and treatment strategy only makes matters worse because hard statistics are scarce and often contradictory. “The problem is that at the moment it is all speculation,” Boscia says. “We are fighting a number of fronts without any artillery—from the vectors that carry the bacterium to the accurate testing of the trees. [The bacterium] lives in the xylem, so an infected tree could have a healthy limb, and if we test the wrong one, we may allow the tree to live and continue to be a host. That’s not comforting to the growers.”

Few experts are as versed in the X. fastidiosa bacterium as Alexander Purcell, a professor emeritus at the University of California, Berkeley, who has written some of the most extensive research on the effects of Xylella on agricultural crops. “The ancient iconic symbolism and cultural impact of the olive tree in Europe and the Mediterranean gives this disease an impact I haven’t experienced with grapes, citrus and other crops that were hit suddenly with Xylella,” he told Scientific American on Skype. “But until the majority of people are willing to cooperate and take action in the local community, nothing is going to slow down.”

If there can be any good news for Puglia’s legendary olive growers it is the fact that the bacterium has no impact on the fruit and oil the healthy trees produce, says Boscia, precisely because infected trees do not produce olives. The only danger to people who consume the unique Pugliese oil is that there won’t be enough to go around. The bad news, of course, is that as the trees are dying, so is a culture that has prevailed for millennia.