The trees are succumbing to a bacterial outbreak that is sweeping across one of Italy’s most famous olive regions, as families that have manufactured olive oil for generations now fear ruin, even as officials in the rest of Europe fear a broader outbreak.

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RACALE, Italy — Across the stony heel of Italy, a peninsula ringed by the blue-green waters of the Mediterranean, olive trees have existed for centuries, shaping the landscape and producing some of the nation’s finest olive oils. Except now many of the trees are dying.

Sprinkled among the healthy trees are clusters of sick ones, denuded of leaves and standing like skeletons, their desiccated branches bereft of olives. The trees are succumbing to a bacterial outbreak that is sweeping across one of Italy’s most famous olive regions, as families that have manufactured olive oil for generations now fear ruin, even as officials in the rest of Europe fear a broader outbreak.

“It is devastating,” said Enzo Manni, director of ACLI-Racale, an olive cooperative in the heart of the outbreak area. “It is apocalyptic. I compare it to an earthquake.”

Today, scientists estimate that 1 million olive trees in the peninsula, known as the Salento, are infected with the bacterium Xylella fastidiosa, a figure that could rise rapidly.

For Italy, which annually produces 500 million tons of olive oil, trailing only Spain, the outbreak has forced a bitter bargain: To prevent the bacterium from spreading north, officials are trying to quarantine the outbreak in the lower half of the Salento, where most of the contaminated trees are, by carving a buffer zone that would serve as a sort of biological firebreak.

The Italian olive industry endured a terrible 2014 from bad weather and a nasty infestation of the olive fruit fly. But those are familiar problems. The bacterial outbreak — which is believed to have arrived with plants imported from Costa Rica and has destroyed citrus trees in Brazil and vineyards in California — poses a new danger for all of European agriculture.

In Brussels, the European Commission has backed off earlier proposals to cull millions of trees in the Salento and, instead, endorsed the Italian buffer zone as well as other surveillance ones north of the peninsula. The commission is also expected to soon finalize a policy that would demand swift culling in the case of any new outbreaks in other regions. And France has moved to protect its vineyards by banning the importation of certain species of plants from Puglia, the region of Italy that includes the Salento.

“The most important thing is that the disease doesn’t spread to the north,” Enrico Brivio, a European Commission spokesman, said, adding of olive growers in the Salento: “We sympathize with them. There are trees that have been there for hundreds of years. They are like monuments.”

Like a slow stroke

To drive through the southern half of the Salento is to realize that the hardest-hit areas surround the coastal town of Gallipoli and radiate southward, toward Racale and then down to the tip of Italy. The bacterium steadily restricts water flow from the roots of a tree to its branches and leaves. The olives are not affected but production gradually diminishes as a tree dies.

“It is like they have a slow stroke,” said Ettore, a local olive producer who would give only his first name because he did not want his company to be associated with the epidemic. “Slowly, it is as if the blood is no longer flowing, and the branches dry out and stop producing olives.”

Standing in the middle of a grove, Ettore, 32, and Manni, the co-op official, nodded toward a tree with a trunk easily 25 feet in circumference. It is called the Giant of Alliste, and local growers say it is 1,500 years old (a figure scientists say is unlikely). It appears healthy, except for one branch in which the leaves are reddened and curled, an early sign that the bacterium has struck.

Manni reached down into a patch of grass, picking through weeds until he pinched what appeared to be a glob of spit but was actually the protective casing for the nymph stage of the spittlebug. The spittlebugs will start flying this month and have served as a primary vector of the outbreak, chewing on the leaves of infected trees and then carrying the bacterium to other, healthy trees, like an unseen wildfire. Scientists say no one yet knows the extent of the outbreak because some infected trees may not yet be showing symptoms.

“There are many,” Manni said, pointing to a few globs in the grass. “Here, here.”

Italian officials, blamed by olive growers for reacting too slowly, have now divided the affected region into quarantine areas, with the buffer zone extending across the peninsula. Infected trees and plants were supposed to be cut down in one of the quarantine areas north of the buffer zone, while growers in the contaminated region south of the buffer zone were supposed to prune infected trees and cut surrounding grasses to better control insects.

But last week, an Italian administrative court suspended olive-tree culling in Puglia. Italy’s Agriculture Ministry has appealed the decision, and culling could resume soon.

Maurizio Martina, Italy’s agriculture minister, said that, at most, about 35,000 trees could be uprooted under the government plan — out of the estimated 11 million olive trees in the area. So far, the ministry said officials have cut down only six trees, with farmers culling an additional 100 or so. But the culling numbers could grow far higher assuming the new court ruling is overturned.

“This is a European emergency that we need to address with a uniform response,” Martina said in an emailed response to questions about the outbreak.

Scientists say that a buffer zone may be useful but warn that simply cutting down infected trees will not solve the problem in southern Salento. “The only feasible option is coexistence — and to create an open sky laboratory in that area,” said Donato Boscia, a scientist at Italy’s National Research Council.

Entrenched problem

To some degree, Europe is simply now facing a problem long entrenched in the Americas. One recent study estimated that Pierce’s disease — a strain of Xylella that affects grapes and vineyards — costs California about $104 million a year. Farmers in Brazil, which produces about 60 percent of the global juice supply, face similar problems.

“They have essentially learned to live with a very high prevalence of Xylella,” said Rodrigo Almeida, an associate professor of environmental science at University of California, Berkeley.

Almeida, who visited the Salento in November 2013, said the genetic testing of the Italian strain showed a perfect match with a strain in Costa Rica — prompting scientists to hypothesize that the outbreak originated several years ago with imported plants.

Almeida said the buffer zone was a “worthwhile idea” but warned that it was too soon to know how far north the bacterium had traveled. “It is difficult to know if it is going to work or not,” he said.

In southern Salento, growers are alarmed but determined to learn how to adapt to the presence of the bacterium. It takes seven years or longer for a new tree to begin producing olives, and farmers were initially furious at reports that the European Commission wanted to cut down 1 million or more trees, and possibly even healthy plants in proximity.

Growers note that about 10 percent of all olive trees in the southern part of the province are infected — meaning that about 10 million trees are still thought to be healthy.

“Our main goal is to save Salento from the bacteria,” said Giovanni Melcarne, a producer and head of a consortium of olive growers. “We need to coexist with it. Eradication is not a feasible goal.”

The other question is who will cover the economic losses for culled trees. Martina, the agriculture minister, recently said 11 million euros (about $12.3 million) would be made available to compensate growers. But the economic impact on Puglia could be much worse.

Most of all, olive growers fear that a way of life that has sustained generations could disappear. Already, production is dropping at many farms in the region.

“We are scared to go to the fields in the mornings,” said Pantaleo Piccinno, a major olive producer who is also president of the local branch of Coldiretti, one of the country’s largest farm associations.

“You leave in the afternoon and everything looks normal. Then you return in the morning, and you see the first symptoms,” he continued.

“It’s going to get much worse.”