Xylella Fastidiosa Containment Protocol Proves Effective in Puglia

Seven years after deploy­ing a pro­to­col com­bin­ing organic treat­ments with a series of other agri­cul­tural prac­tices, treated olive groves demon­strate resilience to Xylella fas­tidiosa.

In Puglia, Italy’s largest olive oil-pro­duc­ing region, which has been ground zero for the coun­try’s dev­as­tat­ing Xylella fas­tidiosa epi­demic, dozens of groves remain as pro­duc­tive as ever. 

The trees are healthy and pro­duce award-win­ning extra vir­gin olive oil. One farmer involved in the pro­to­col earned Gold Awards at the 2020 and 2021 edi­tions of the NYIOOC World Olive Oil Competition.

The results of the pro­to­col’s deploy­ment were pre­sented at the 14^th International Conference on Plant Pathogenic Bacteria in Assisi by the researchers who study the spread of the deadly olive tree bac­te­ria, which causes olive quick decline syn­drome.

“The pro­to­col is work­ing. When cor­rectly deployed, it pro­vides safe pre­ven­tion, a shield against the effects of Xylella,” Marco Scortichini, the lead researcher for olives and fruit crops at the Italian Council for Agricultural Research and Economics, told Olive Oil Times.

Scortichini and other researchers pub­lished two stud­ies in the Phytopathologia Mediterranea and Pathogens sci­en­tific jour­nals in 2018 and 2021, demon­strat­ing the results of the con­trol strat­egy adopted in Salento, the Apulian ter­ri­tory most severely impacted by Xylella fas­tidiosa.

During the con­fer­ence, Scortichini said the con­cen­tra­tion of Xylella fas­tidiosa bac­te­ria in infected and treated trees sig­nif­i­cantly dimin­ished over time, up to 50 per­cent less than in infected and untreated trees.

The pro­to­col requires farm­ers to remove veg­e­ta­tion that pro­vides shel­ter to the known dis­ease vec­tors, such as the meadow spit­tle­bug. 

They are also asked to peri­od­i­cally prune and spray their trees with an organic antibac­te­r­ial treat­ment that has effec­tively cur­tailed the spread of Xylella fas­tidiosa. 

In a region where olive grow­ing is as much a fam­ily tra­di­tion as an eco­nomic activ­ity, not all small farm­ers are ready to fol­low a sys­tem­atic approach to which larger farms and com­pa­nies can more eas­ily adapt.

“Whereas the pro­to­col does not work, fail­ure is always asso­ci­ated with an inef­fi­cient approach, where com­pli­ance is lost,” Scortichini said. ​“We need to change their men­tal­ity, improve pro­fes­sion­al­ism and be con­sis­tent.”

The antibac­te­r­ial agent stems the spread of the dis­ease in the infected tree. However, it does not elim­i­nate the infec­tion. Researchers are still study­ing to what degree a treated olive tree, kept healthy and pro­duc­tive by the pro­to­col, might become a source of fur­ther infec­tion. 

“With this pro­to­col, Xylella becomes for the olive tree what downy mildew is for vines,” Scortichini said. ​“For the con­tain­ment to work, you need to deploy the treat­ment every year and every month between March and September.” 

“By devel­op­ing the pro­to­col, the goal was not to erad­i­cate Xylella, as it is an unfea­si­ble goal, but to con­trol it sim­i­larly to other plant dis­eases,” he added.

Treated groves stand out in the Xylella-hit region; their trees boast a green and healthy crown, often sur­rounded by the remains of orchards rav­aged by Xylella fas­tidiosa.

“Beating Xylella does not come at a low cost, though,” Francesco Paolo D’Urso, owner of Masseria Curtimaggi, a two-time NYIOOC award win­ner, told Olive Oil Times.

D’Urso’s farm cov­ers 250 hectares, where he grows approx­i­mately 40,000 olive trees. The farm started apply­ing the pro­to­col in 2016, two years after the first dis­cov­ery of Xylella in the region.

“Every year since then, I have to pro­ceed to treat my trees sev­eral times, and the organic prod­uct by itself costs me between €35,000 and €40,000 – €150 to €160 per hectare – which means it con­sid­er­ably reduces our final income,” he said.

The treat­ment price varies between €10 and €15 per liter, which D’Urso believes may have dis­suaded some small farm­ers from imple­ment­ing it each year. 

However, he added that the sight of his olive trees infected with Xylella is too painful to bear, which is why he read­ily pays for the treat­ment.

“By explor­ing dozens of cases where the pro­to­col has been applied, we have deter­mined that its suc­cess comes from the con­sis­tency of the treat­ments, prun­ing and cur­tail­ing of the vec­tor insects between February and May,” Scortichini said.

“From the own­ers of small and medium farms and pas­sion­ate part-time grow­ers to pro­fes­sional con­texts, such as a 10-hectares farm in Nardò or the D’Urso com­pany, those who fol­low the pro­to­col har­vest an aver­age of 30 to 40 quin­tals [300 to 400 kilo­grams] per hectare,” he added.

In a region where Xylella fas­tidiosa has killed hun­dreds of thou­sands of trees in less than a decade, farm­ers who are actively apply­ing the pro­to­col cover an over­all sur­face of 200,000 hectares. 

“They grow the tra­di­tional local cul­ti­vars; noth­ing has changed, such as Cellina di Nardò or Ogliarola,” D’Urso said. ​“Thanks to such an exten­sive treat­ment area, we can now see the pro­to­col’s results.”

“When we began to deploy the pro­to­col, Xylella was mak­ing the head­lines,” he added. ​“There had been a few cases not far from us, and there were meet­ings with farm­ers and experts to explore the sit­u­a­tion.” 

“Since then, around us, there have been so many dead trees, so many orchards have seen their pro­duc­tiv­ity fall, and their trees get sick because of Xylella,” D’Urso con­tin­ued.

One of the chal­lenges test­ing the resilience of local farm­ers has been deal­ing with aban­doned or semi-aban­doned olive groves, where these treat­ments are not being applied.

“Many large landown­ers did not main­tain their prop­er­ties, and that made it eas­ier for the vec­tor insect to mul­ti­ply,” D’Urso said. ​“At the begin­ning, many opposed the idea to remove the infected plants.” 

Regional and national laws and reg­u­la­tions now require landown­ers to fol­low these prac­tices. 

According to D’Urso, among the advan­tages of the pro­to­col is its effi­cacy in com­bat­ing another sig­nif­i­cant pest, the olive fruit fly.

“We have seen that apply­ing that pro­to­col and adding a few other organic solu­tions, we can dras­ti­cally curb the repro­duc­tion of the olive fruit fly,” he said.

Researchers at the University of Padova have also con­firmed his obser­va­tions. 

“By work­ing in lab con­di­tions to cur­tail the olive fruit fly, they deployed a series of sus­tain­able solu­tions and con­ven­tional prod­ucts,” Scortichini said. ​“They found the Xylella antibac­te­r­ial prod­uct is almost as effi­cient as the long-used chem­i­cals.”

“The rea­son is the antibac­te­r­ial charge of the prod­uct, which kills bac­te­ria whose pro­teins feed the fruit fly lar­vae,” he added. 

The antibac­te­r­ial treat­ment has also proven effec­tive against the brown mar­morated stink bug, which is respon­si­ble for dam­ag­ing olive groves in south­ern Europe and sev­eral other crops. 

According to Scortichini and D’Urso, the Xylella treat­ment pro­to­col should con­tinue to be explored to pre­vent fur­ther dam­age. 

“It might not be the defin­i­tive solu­tion, but it can be part of a broader effort,” D’Urso said. ​“Two of our trees were recently found to be poten­tially infected by new aer­ial detec­tion sys­tems that can quickly scan hun­dreds of trees to reveal poten­tially infected ones.” 

“After the scan, experts came to our fields to take sam­ples, and we are now wait­ing to know the result of their analy­sis, to know if Xylella was found,” he added.

The most sig­nif­i­cant chal­lenges for local grow­ers are the rel­a­tively low extra vir­gin olive oil prices com­pared to the his­toric highs between 2016 and 2018 and the rules applied in the Xylella-affected areas that do not take the indi­vid­ual pre­ven­tion meth­ods deployed by farm­ers into account. 

“The local author­i­ties are now ask­ing farm­ers to apply a prod­uct based on pyrethrum which can cost up to €70 per liter,” D’Urso con­cluded. ​“A manda­tory treat­ment whose ratio­nale is unin­tel­li­gi­ble for a farm like ours, where Xylella has been actively and effi­ciently con­tained for sev­eral years now.”