The legendary olive trees of Puglia produce some of the finest oil in the world. Thousands of farm families have pressed the fruits for generations. The trees' twisted trunks—some radiocarbon-dated at more than 2,500 years old—are as fundamental to the landscape here as the castles and the sea. They have persisted through centuries of invasions, wars, droughts and depressions. No matter how bad things have ever gotten, the orchards have always provided promise for the future. That's why the spontaneous death of these trees, presumably by a foreign bacterium called Xylella fastidiosa, feels like a black plague. Carried by insects, the bacterium has swept through grove after grove.

Authorities have reacted with extreme measures. On July 7, Giuseppe Silletti, head of the Puglia division of the State Forestry Corps and special commissioner in charge of eradicating Xylella, ordered two dozen of his men to sweep into an area with several small groves near Oria at 5 A.M. to cut down more than 40 olive-laden trees. They arrived, chain saws blaring, without warning any of the owners or the local mayor, Cosimo Ferretti. More than 30 special armed police, generally dispatched to control riots, arrived with them to hold back the farmers and their families and neighbors. The owners watched in horror while the uniformed men massacred the ancient trees and yanked the gnarled roots from the ground, as if to symbolize the destruction of the region's deep-rooted heritage. Angry residents raised their fists and screamed, “Murderers!” Two women in their 50s—third-generation growers who were infuriated that their orchards were among those being razed—began to hit the police and were escorted away.

Such raids take place regularly now. In just two years since Xylella was first identified in the “heel” of Italy's “boot,” known as the Salento, more than one million olive trees are dead, either withered by Xylella or killed by authorities trying to contain the disease's spread. But farmers and activists claim that the eradication is a farce because authorities offer no proof that the trees they destroy have the disease.

Science has an uneasy place in Italy. After all, this is the country where a court of law convicted six scientists and a government official of involuntary manslaughter for not predicting a 2009 earthquake that struck L'Aquila. The scientists' convictions were eventually overturned by a higher court, but general mistrust of science is as Italian as olive oil itself. This past spring police raided offices at the main research center for Xylella in Bari, carrying out computers and boxes of files, apparently looking for a money trail or something else to prove that the presence of the bacterium is no accident. The tense relationship makes scientists reticent when they do not have ironclad data, which feeds a vicious cycle of suspicion.

It does not help that of the estimated 60 million olive trees in Puglia, only 30,000 are under surveillance for the disease by local researchers, yet hundreds of thousands are at risk of eradication. Trust is also missing because even the most learned experts, in Italy and around the world, do not know exactly how Xylella would kill an olive tree, which leaves open the troubling question of whether the bacterium is causing the scourge. It is present in many dead trees, but so far no one in authority has been able to connect events with a clear line.

Some research suggests Xylella stops water from flowing from the roots to the leaves, causing a tree to dry up. Other factors may contribute to actual death, however, such as common parasites and fungi, but scientists have yet to confirm or deny their roles. Part of the challenge is that when Xylella occurs in other plant species, it behaves differently, and its carriers can be more easily contained. Puglia is the first place Xylella has attacked olive trees, so there is no historical research. Some experts think it was introduced when a local garden center imported infected oleander plants from Costa Rica, where the same strain has been documented (there are three different strains).

Understanding if and how Xylella may have crossed over to olive trees would be a research triumph. But authorities are not waiting to find out. They do not test most dead trees because of lack of funding, as well as an overwhelming sense that they have to take action, now, to stop any further spread. The big fear is that the disease will advance northward, attacking the heart of Puglia's lucrative olive industry, which produces more olive oil than any other part of Italy. Neighboring countries also fear the scourge will move up through the continent, perhaps even crossing over to grapes, almonds and cherries. Agriculture officials say Puglia will lose more than $225 million in olive oil production this year alone, but if the heart of the region succumbs to the bacterium, that figure could easily quadruple, driving up the price of oil worldwide.

One issue the scientific community agrees on is that even though Xylella is almost certainly carried by the meadow spittlebug, the widespread use of pesticides to stop the insect would cause serious collateral damage, poisoning the current olive crop and making the fruit and oil unfit for consumption for up to a decade. The chemicals would also kill surrounding plant life. Agronomists say, at best, pesticides could only be used, carefully, in underbrush during spittlebug nesting. That is why the scientific and agricultural communities in the European Union maintain that the only way to stop the disease is to create a buffer zone—to kill all the trees in a wide west-to-east swath between the dead and dying trees south of Lecce and those yet uninfected to the north. If Xylella is found on a single tree anywhere near the buffer zone, every tree within 100 meters (328 feet) is spray-painted with a red X that drips like blood down the thick, craggy bark, to signify that it must also be destroyed. Then, without notice, the forestry corps agents arrive with their chain saws.

The farmers, who know the groves best, insist that many of the marked trees are healthy and do not need to be sacrificed. Scientists on testing trips around Puglia are scrambling to improve the data. But the men with chain saws are one step ahead of them.

Death to insects and trees

Donato Boscia, a virologist in charge of the Bari unit at the National Research Council of Italy's Institute for Sustainable Plant Protection, is the leading scientist on the front line of the ill-informed battle. He maintains an awkward balance between directing research and placating a population that views almost everything he does with skepticism or contempt. He is also the man who first identified the bacterium in 2013, in olive groves owned by his father-in-law south of Lecce. “I knew this was something big,” he told me at his greenhouse laboratory in Bari, as he recalled how his father-in-law summoned him to his groves to show him “something wrong.” “What I didn't know then was that by now, almost two years later, we still wouldn't have a cure or that we would have faced so many obstacles and lost so much valuable time trying to contain the spread.”

Boscia is referring to what has become a frustrating game of resistance to even the most basic prevention suggestions. He is one of several scientists under judicial investigation for potential wrongdoing in handling the aftermath of the outbreak. Yet he chooses to forge ahead, playing tug-of-war between what should be done to save the trees and what will be achievable in reality.

For instance, because the widespread use of pesticides to obliterate the spittlebugs is not a viable option, he says that good farming practices are crucial to reducing the bug population, including clearing the underbrush of weeds where bugs nest and very controlled spot spraying of insecticides when the spittlebugs are on the canopy of trees. But many farmers refuse to even try spot spraying, he says, out of fear they won't be able to use their oil. “There is no one weapon to fight this bacterium, so we need to implement an integrated plan aimed to control the [spread],” he says, referring to both better farming practices to thin out the bugs and cutting trees in the buffer zone to stop the bugs from advancing geographically. “But even that won't work unless everyone follows it.”

One of the few certainties in this drama is that insects infected with Xylella transmit the bacterium as they move from tree to tree and puncture the trees' xylem to feed (the xylem is plant tissue that carries nutrients). The presumed enemy, the meadow spittlebug, is abundant in the region. But cicadas, whose grinding love songs are almost deafening throughout Puglia's olive groves, may also spread the bacterium. At the time of this writing, however, cicadas had not been systematically examined, because they are nearly impossible to catch in great enough numbers for clinical analysis.

Even though testing shows Xylella is present in many dead trees, local farmers and activists are angered because so many trees go untested. They want all the groves under surveillance. According to a report sent to the E.U. by Italy's agricultural ministry in July, just 33,600 inspections out of more than 60 million trees have been conducted across Italy since the initial outbreak. Hundreds of agents from Italy's National Research Council and the State Forestry Corps have monitored more than 152,000 acres of olive groves, but so much more area is involved that no one can yet say whether the disease is endemic to the region.

Technicians take samples to one of two labs for testing. Most of the samples from the Salento go to the agricultural research center CRFSA “Basile-Caramia” in Locorotondo, run by Vito Nicola Savino. He told SCIENTIFIC AMERICAN that his small staff has had to delay other projects to concentrate on testing and research dedicated to Xylella. His hope is that the global scientific community will soon start to study the dying trees in situ, in a proposed open-air lab, to better understand the disease's devastating effects. That project was green-lighted by the region's previous governor but then largely forgotten when he lost his job in an election this past spring. “We have the opportunity here to be a world leader in the study of this phenomenon,” Savino says. “We have a new occurrence of Xylella affecting a species in a way that is completely unexpected.”

He also believes that eradication is fundamental because trying to stop the spread by insects (called vectors) is proving impossible without widespread pesticide use. In many ways, the scientists, backed by the E.U., have come up with a prescription of extensive cutting without knowing all the facts. Authorities are going on faith that if they get rid of trees in the buffer zone, the spittlebugs will have nowhere to feed and potentially die off, or at least they will stay contained in the infected area. Savino has signed on. “We have to get rid of the infected plants before we can possibly hope to destroy the vectors,” he maintains. “There is no other way to win this battle.”

Conspiracy theories

Because the eradication area is where the bulk of the region's monumental trees have thrived for centuries, farmers strongly oppose the plan, believing that authorities are unnecessarily panicking and that there must surely be a better way. How, they wonder, could trees that have survived so long be wiped out entirely? Why, if Xylella has been contained without drastic eradication in other parts of the world when it attacked different plant species such as grapes in California, can it not be effectively contained in olive groves in Puglia? When the bacterium caused Pierce's disease in grapes in California, Florida and Texas, pesticides, radical pruning and crop replacement with Xylella-resistant varieties successfully contained the disease. Although it might take a decade or more to establish productive, Xylella-resistant olive trees, the growers note that that is almost overnight in an industry that has flourished for two millennia.

Because scientists cannot answer such basic questions, the gap between the opposing sides widens. Hard data are scarce, so the scientists and local authorities tend to stay silent, which many growers interpret as a cover-up for ulterior motives. Ask anyone in Puglia what they think of Xylella, and you get a range of conspiracy theories: that the American firm Monsanto introduced a genetically modified strain of the bacterium in Puglia so it could sweep in with a cure; that a British land developer with dreams of turning Puglia into a golf Mecca has used sinister means to clear the land so he can buy it cheap. None of this can be proved, but neither can the prevailing scientific theory that Xylella was introduced in a shipment of exotic plants from Costa Rica.

The lack of cooperation worries the rest of the continent. This past January the European Food Safety Authority issued an apocalyptic warning: “X. fastidiosa may affect several crops in Europe, such as citrus, grapevine and stone fruits (almond, peach, plum), but also several tree and ornamental plants, for example, oak, sycamore and oleander.... The probability of establishment, following an entry of X. fastidiosa, is rated as very likely.” The agency supports the plans for a buffer zone but calls into question the effectiveness of eradication without mandating proper farming practices, including spot pesticide use.

Some steps are starting to happen—ironically, in areas south of Lecce, which Boscia describes as “hit by an ecological bomb.” The farmers there have been left to decide how to protect the few trees that remain healthy among the stumps that stand like remains of deceased soldiers in a battlefield, hoping that those ghosts will miraculously come back to life.

The farmers there are experimenting with organic treatments, coupled with age-old traditions, including grafting limbs of healthy trees onto those that are sick. It is too early to know if they might succeed. This is also the place where Savino would have implemented his ambitious plan to build an open-air lab to study the effects of the disease. In a brief moment of optimism this past spring, the local government pledged €2 million to build an international research center for it, but the elections changed that.

Distrust in science

North of the affected area, in the buffer zone, talk is more defiant. Standing in his grove, farmer Pasquale Spina tells me in angry tones that the disease is a figment of the scientists' imagination, as he strokes new green stalks sprouting from a stump cut under the eradication plan. “History tells you how difficult it is to kill an olive tree,” he says, pointing to ancient trees nearby that are scarred from lightning strikes and parasites. “The trees are sick maybe, yes, but they are sick for other reasons, not Xylella. You don't have to kill these trees that have survived everything that came at them. Why now, when we have such scientific advancements, do 1,000-year-old trees have to die like this?”

That, of course, is the billion-dollar question. There is perhaps no one more versed in Xylella than Alexander Purcell, a professor emeritus at the University of California, Berkeley, who has published extensive research on the impact of the bacterium on agricultural crops. He believes Xylella is responsible for the death of the trees south of Lecce, having visited the area after the outbreak was first confirmed. He recalls the moment when a spittlebug landed on the windshield of a car he was riding in and stayed there for miles, proving how easy it is for potentially infected vectors to move. Hence, he is not a fan of the full-eradication plan. The best approach, he insists, is a combination of limited pesticide use and good farming practices in addition to culling infected groves. “There are a lot of things about Xylella that we don't understand,” he says. “But it is going to take a cascade of control efforts to beat this. No single silver bullet is going to do it.”

Purcell says the Italian scientific community has a great responsibility to study the effects of Xylella on a new crop, but he admits that unless there is more transparency and trust, the effects on groves—as well as the lost opportunities for research—could be devastating. “If diseased tree removal is such a difficult obstacle to overcome—maybe impossible in rural Italy—how hard will it be to overlay area-wide insecticide use?” he asks. “Only the combination might have any effect.” He adds that experts would know if the approach works only after trying it for several years. “Do you think that the Italian citizenry will support this?” he asks.

Maybe not, but Purcell believes the experts should try. The economic fallout of this new epidemic could be striking, he notes. And the cultural importance of the olive tree in the Mediterranean “gives this disease an impact I haven't experienced with grapes, citrus and other crops that were hit suddenly with Xylella. Many ancient trees along the Mediterranean have survived centuries with little care,” Purcell adds.

Purcell does not have a concrete answer for the larger issue, either: the disease's sudden appearance and devastating effects. “Why in Europe now, when the pathogen has been living in a huge diversity of plants in the Americas for so long?” he wonders.

Doubt stalls a cure

The tree owners wonder, too. Scientists will have to overcome their reluctance to talk and conquer the prevalence of conspiracy theories to gain trust and guide tree owners out of the crisis. Open dissemination of reliable information, even if it is not conclusive, is key. But clarity can be difficult to find. Francesca Mandese, a reporter for the newspaper Corriere del Mezzogiorno has been following the spread of Xylella since the first olive leaves showed symptoms. She says her biggest challenge is finding the balance between the scientific community's lack of transparency and the activists' zeal. “It leaves me perplexed that no one seems to be certain about anything,” she says. “Instead it is always ‘maybe’ and ‘probably.’ In the end, you can't just destroy thousands of trees without being certain.”

That doubt also causes knee-jerk reactions by some farmers. Out of fear that their trees will be culled, many growers now try to hide symptoms of the drying effects of Xylella. When they see so much as a dead branch on their trees, they immediately prune the limb or, in some cases, burn the tree entirely before anyone can alert inspectors.

Purcell suggests that the best hope for growers in Puglia is to harness recent advancements in genetic engineering and start over with new olive tree varieties that are Xylella-resistant. It has taken 10 years or more for that approach to produce decent grapevines in California, and he says success could take twice as long in Puglia. “The cost in time and money will be enormous. But it is still better to start now instead of later. The economic and ecological payoffs in breeding are always manyfold greater than their costs.”

Purcell's words may not inspire the people of Puglia. What they know for certain is that Xylella has not affected olive oil whatsoever, simply because the sick trees do not produce olives. Angela Amico is a proprietor of the well-known Cibus restaurant here. She and her husband produce olive oil for their customers from trees that may soon be painted in red for eradication, even though she says her trees are more fruitful now than they have been for a decade. She has faith that the trees can survive on their own, just like they have done for millennia. “My olives have never looked better,” she says. “What more proof do I need that my trees are healthy?”