Can Xylella Be Stopped?

Five years into the Xylella fastidiosa tragedy, scientists fear its continued spread may be inevitable.

Gennaro Santoro (Photos: Cain Burdeau for Olive Oil Times)
May. 4, 2018
By Cain Burdeau
Gennaro Santoro (Photos: Cain Burdeau for Olive Oil Times)

Recent News

The set­ting is a mellow fall day in the vine­yards of the Santoro Tenuta in the Valle d’Itria, an agri­cul­tural won­der­land now the epi­cen­ter of efforts to stop the spread of Xylella fas­tidiosa, a lethal plant bac­terium killing thou­sands of olive trees here in Puglia, the boot-heel of Italy.

This is a stun­ning epi­demic, and it must be dif­fi­cult if not impos­si­ble to over­come the grief over the loss of cul­tural icons that have endured for cen­turies.- Rodrigo Almeida, University of California at Berkeley

Gennaro Santoro, a 75-year-old vint­ner, was clip­ping away at grapes left dan­gling after the har­vest. His vine­yard is sur­rounded by olive orchards and he tends to olives around the tenu­ta’s winery.

I knew Gennaro from pre­vi­ous visits to the Valle d’Itria, and stopped in to hear his thoughts on Xylella, an omi­nous plant dis­ease spread­ing in Europe from the New World that is the sub­ject of an Olive Oil Times series.

Scientists com­pare what is hap­pen­ing today among olive orchards to what hap­pened in the late 1800s in Europe with wine grapes. An aphid-like insect, the grape Phylloxera, was brought to England from the New World and wreaked death in Europe’s vine­yards.

Gennaro Santoro’s own vine­yard dates to that period when Phylloxera invaded France and spread to the rest of Europe. For sev­eral decades Puglia was untouched by Phylloxera and became wealthy sup­ply­ing wine-starved Europe.


Gennaro Santoro (Photos: Cain Burdeau for Olive Oil Times)

“Yes, I will talk about that, about Xylella” Gennaro said ami­ably. “But let me show you first the autochtho­nous vines we’ve planted!” He’s a learned farmer of Swiss-Italian ori­gins whose family goes back gen­er­a­tions in this con­trada, an Italian word for a small rural com­mu­nity or vil­lage.

With a back­ground in biol­ogy and some­one steeped in local his­tory, his tour lasted an exhil­a­rat­ing hour.

He strolled the rows of vines, waved his prun­ing clip­pers in the air, and all the while recounted of feudal estates, the masserie founded by ex-Roman sol­diers, and sub­se­quent peas­ant revolts; and how even­tu­ally the brac­cianti, the peas­ants, came into pos­ses­sion of the valley.


Looking at the green hills run­ning with rock walls, he offered ever more his­tory.

“This was where Byzantine monks once stopped to give water to their herds, during the tran­shu­mance. You see, a foggia is a long ditch they dug to carry rain­wa­ter into the Murgia, where there’s no river, and no wells. There was a foggia here, and it was called Sauro.”


We got back to my vehi­cle in the small park­ing lot behind his fam­i­ly’s winery, where a few olive trees grow. The sun was set­ting and dinner time approached.

“But what about Xylella?” I asked him again.

He winced. “It’s all wrong. You can’t cut down all the olive trees. We must seek to live with the dis­ease, as farm­ers have always done.”

He was opti­mistic, though, and cer­tainly didn’t think the olive trees dot­ting his piece of coun­try­side would fall vic­tims to Xylella and die.

“We aren’t wor­ried about our trees dying because we are organic,” he said con­fi­dently. “No one uses her­bi­cides around us because it is out­lawed.” Before bid­ding farewell, he added: “You can’t com­mand nature. But you can adapt.”

His sen­ti­ments about Xylella go to the heart of a raging sci­en­tific and agro­nomic debate grip­ping Puglia, Italy’s most pro­duc­tive olive region.

The last five years have been riven with Xylella head­lines, protests, polit­i­cal intrigue and a razed-earth strat­egy that has seen the clear-cut­ting of thou­sands of olive trees in Salento, a flat olive-rich area of south­ern Puglia.


“This is a stun­ning epi­demic, and it must be dif­fi­cult if not impos­si­ble to over­come the grief over the loss of cul­tural icons that have endured for cen­turies,” said Rodrigo Almeida, a Xylella expert at the University of California at Berkeley.

Now, five years into the tragedy, it’s becom­ing ever more omi­nous that the battle to erad­i­cate Xylella may have been lost and sci­en­tists fear its spread may now be unstop­pable and poten­tially even spread faster.

Scientists analyze olive samples for Xylella fastidiosa

Alexander Purcell, another Xylella expert at the UC-Berkeley, said that the dis­ease is “so preva­lent in most of Salento that erad­i­ca­tion of Xylella is no longer con­sid­ered pos­si­ble.”

In December, Vytenis Andriukaitis, the European Commissioner-des­ig­nate respon­si­ble for Health and Food Safety, warned that Xylella had become “the biggest phy­tosan­i­tary crisis con­fronting the EU for many years.” He made his com­ments in Paris.

What to do then? Cut or not cut sick olive trees and their neigh­bors? It’s here that sci­en­tists are divided.

For now, the strat­egy remains to cut down and erad­i­cate sick trees in areas where author­i­ties are seek­ing to stem the dis­ease’s spread, an area where Gennaro Santoro’s vine­yard and olive trees are.

The dis­ease appeared in the region about five years ago when farm­ers and sci­en­tists started inves­ti­gat­ing the sudden brown­ing of olive leaves on trees near the port of Gallipoli in Salento.

The iconic olive tree is an ever­green – so any brown­ing is cause for alarm.

Since Xylella fas­tidiosa was declared the cul­prit in 2013, the EU has demanded Italy under­take a rad­i­cal erad­i­ca­tion pro­gram to stop the spread.

Whether it’s lack of action by Italy or the sheer nature of the bac­terium, erad­i­ca­tion efforts have failed. And Xylella is on the march.

So far this year, hun­dreds of new trees are being cut down in areas not far from the Santoro vine­yards.

The number of infected trees has quadru­pled in one year in the crit­i­cal con­tain­ment zone, accord­ing to ANSA, the Italian news agency.

Another omi­nous devel­op­ment is taking place across the Mediterranean: Olive trees in main­land Spain are begin­ning to die due to Xylella, accord­ing to Spanish author­i­ties and news reports. Spain is the world’s largest olive oil pro­ducer.

So far, though, Puglia is where death has been fiercest.

Tens of thou­sands of trees have been infected and thou­sands either cut down to pre­vent the spread of the dis­ease or are dying due to infes­ta­tion.

“The only way to fight it is the com­plete erad­i­ca­tion of infected trees and their sur­round­ings as so far no treat­ment exists for the bac­te­ria,” Andriukaitis, the EU Commissioner, said in an email to Olive Oil Times.

He added that the dis­ease could worsen due to cli­mate change and glob­al­iza­tion of trade.

“Since pests respect no bor­ders every­one must play their part to keep plants healthy across the EU and to avoid seri­ous con­se­quences for our agri­cul­ture, our econ­omy and our local com­mu­ni­ties,” he said.

In Puglia’s areas where the bac­terium has already wreaked havoc and where sci­en­tists say it can no longer be erad­i­cated, farm­ers are left having to cope with the bac­terium.

“Co-exis­tence with this sick­ness is a goal the whole sector wants to get to,” said Marco Scortichini, a plant bac­te­ri­ol­o­gist at the Council for Agricultural Research and the Analysis of Agricultural Economics, an Italian research arm that spe­cial­izes in olive cul­ti­va­tion.

“Reduction of bac­terium inci­dence will not be impos­si­ble,” he said in a tele­phone inter­view. “Co-exis­tence is some­thing that can be achieved.”

“I don’t doubt it’s Xylella (killing trees),” said Christos Xiloyannis, a plant phys­i­ol­o­gist at the University of Basilicata, in a tele­phone inter­view. “It’s a ques­tion about how to inter­vene.”

Funds have poured into under­stand­ing and com­bat­ing the dis­ease and sci­en­tific stud­ies have been pub­lished look­ing at Xylella from nearly every angle: How does it spread? How does it stran­gle plant tis­sues? What vari­eties are resis­tant? How best to spray against the bac­terium? How to graft infected trees? How to mon­i­tor the infes­ta­tion?

Science has answers to a lot of these press­ing ques­tions and impor­tant break­throughs have been made. Perhaps the most impor­tant dis­cov­ery has been that some vari­eties of olives are nat­u­rally resis­tant to Xylella — a fact giving hope to many farm­ers who are now replant­ing with a resis­tant Leccino vari­ety.

But there are other projects under­way too. For exam­ple, some farm­ers are seek­ing to replen­ish their orchards by graft­ing Xylella-resis­tant stocks onto old trunks.

Measures to combat the vector, a common spit­tle­bug, have been imple­mented too. Landowners now face hefty fines for not till­ing or cut­ting the grass in their fields to kill the spit­tle­bugs that grow in weeds.

An experiment to artificially infect a tree with Xf, part of efforts to find resistant olive varieties

Among the promis­ing field­work is one Scortichini is work­ing on in Salento. His latest study, which appeared in April in the sci­ence jour­nal Phytopathologia Mediterranea, showed that a copper-based spray was show­ing pos­i­tive results in com­bat­ing the bac­terium. Other sci­en­tists have ques­tioned the study’s find­ings as far from con­clu­sive.

“When it comes to trees, forests, you can’t cut them all down,” Scortichini said.

This is a common state­ment among agron­o­mists, sci­en­tists and farm­ers. They say olive trees are unlike other infected crops – whether animal or plant.

Why? Because they are unique ever­green fruit trees that can sur­vive cen­turies. In this sense, this olive sick­ness is at a dif­fer­ent scale than Mad Cow Disease in Great Britain and even the Phylloxera out­break. Under this view, cut­ting down trees is not the solu­tion and it’s not viable.

“Our advice is to return to the coun­try­side and spend time cul­ti­vat­ing,” Xiloyannis said. “We’ve never been able to erad­i­cate dis­eases that have appeared in the last 30 – 40 years.”

He said it was very likely that Xylella broke out in Salento because olive orchards had become aban­doned and poorly man­aged, making them sus­cep­ti­ble to pathogens.

In part, the European Union is to blame for this, he said, because it was encour­ag­ing farm­ers to cul­ti­vate in this manner.

Xiloyannis said he is work­ing with farm­ers to improve their land prac­tices to fend off the dis­ease – an echo of what Gennaro Santoro, the vint­ner, said about his con­fi­dence in his trees. As of April, the trees on the Santoro vine­yard had not been infected, his son, Marco Emilio Santoro, told Olive Oil Times.

Xiloyannis said cut­ting and replant­ing new olives is simply not fea­si­ble in many areas of Puglia and there is no guar­an­tee that cut­ting old trees and replac­ing them with a resis­tant-vari­ety will work in tough ter­rains.

Still, plant­ing the Leccino and pos­si­bly other bac­terium-resis­tant vari­eties, for now, appears to be the only way of com­bat­ing Xylella, some sci­en­tists say.

“At present, the only pos­si­ble thing which seems to work, albeit data are still pre­lim­i­nary, seems to be plant­ing resis­tant olive vari­eties,” said Enrico Bucci, a sys­tems biol­ogy researcher at Temple University, in an email.

Xylella Marches On: Lethal Olive Disease Discovered in Central Spain

Xylella fas­tidiosa, a plant bac­terium native to Central America that causes seri­ous, often lethal, plant dis­eases con­tin­ues to kill tens of thou­sands of olive trees in south Italy’s Puglia region and it is also on track to widen its deadly clasp across the Mediterranean basin. New reports this spring from Italy and Spain are grim.

This is the focus of Donato Boscia, a lead­ing researcher into the Xylella out­break at the Institute for Sustainable Plant Protection in Bari.

“There is no cure for Xylella at this point,” he said in a tele­phone inter­view.

For now, he is work­ing in Salento to find olive cul­ti­vars resis­tant to the bac­terium. He said research has shown the Leccino and Favolosa vari­eties are resis­tant and he is opti­mistic many more may be too.

The prospect of this remedy eerily hear­kens back to Phylloxera.

Both pests are native to the Americas. Both cause leaves to brown and die, stran­gling and killing its host plant, and both move on to find the next victim.

In the end, Europe learned to live with Phylloxera, but only after nearly every vine­yard was replanted with wild American root­stocks that are resis­tant to the root-destroy­ing bugs.