New Treatment for Xylella-Infected Trees Is Working, Researchers Say

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The appli­ca­tion of an organic treat­ment, com­bined with good farm­ing prac­tices, can allow the olive trees to return to full pro­duc­tion after suf­fer­ing from an out­break of Xylella fas­tidiosa, accord­ing to new research from the Council for Agricultural Research and Agricultural Economics Analysis (CREA).

“We exper­i­mented with a com­pound based on zinc, cop­per, and cit­ric acid – pro­tected by an inter­na­tional patent – that can be used in organic agri­cul­ture and is poten­tially capa­ble of reach­ing the bac­terium in the olive tree xylem,” Marco Scortichini, the research direc­tor of the Olive, Fruit Trees and Citrus Center at CREA, told Olive Oil Times.

“According to stud­ies car­ried out in the United States, zinc and cop­per ions show the great­est con­tain­ment capac­ity of the bac­terium, which can be also curbed by the proper man­age­ment of micronu­tri­ents in the plant,” he added.

Based on the European reg­u­la­tions for the man­age­ment of quar­an­tine pathogens, such as Xylella fas­tidiosa, the erad­i­ca­tion of the bac­terium is the first solu­tion pro­posed as a means of restor­ing infected areas.

“We have to con­sider that the suc­cess­ful elim­i­na­tion of phy­topath­o­genic organ­isms from a ter­ri­tory should be based on well-defined premises includ­ing the imme­di­ate iden­ti­fi­ca­tion of the dis­ease agent, an infected area of reduced dimen­sions and favor­able bio­log­i­cal char­ac­ter­is­tics,” Scortichini said. ​“In my opin­ion, at the time of the dis­cov­ery of the dis­ease, none of these cri­te­ria was man­age­able in a deci­sive man­ner.”

Xylella fas­tidiosa lives not only in the olive tree, but also in sev­eral cul­ti­vated and wild plants. It is trans­mit­ted by a very pro­lific and wide­spread insect car­rier, Philaenus spumar­ius.

Previous attempts to elim­i­nate the bac­terium from all the infected ter­ri­tory, which includes arable land, uncul­ti­vated areas, parks and gar­dens, appeared tech­ni­cally imprac­ti­ca­ble to the researchers and des­tined not to resolve the sit­u­a­tion.

Then they began exper­i­ment­ing with the afore­men­tioned organic com­pound, com­bined with appro­pri­ate farm­ing prac­tices. These include remov­ing weeds and other vec­tors for the spit­tle­bug that may be grow­ing in the groves and prun­ing the olive trees in order to allow bet­ter absorp­tion of the com­pound.

After three years of tri­als and fol­low-ups, the research group con­cluded that the prod­uct is an effec­tive bac­te­ri­cide and remark­ably sys­tem­atic, lead­ing to a sig­nif­i­cant reduc­tion of symp­toms and bac­te­ria pop­u­la­tions inside the trees.

The tri­als also con­firm that the com­pound is not phy­to­toxic to olive trees and no residue from the com­pound could be detected in the oil pro­duced from the olives of the trees.

Over time, sev­eral farms started to adopt the pro­to­col and have been con­stantly mon­i­tored by the research group.

“We started to imple­ment this treat­ment and, pretty fast, we had good results vis­i­ble with the naked eye, there­fore we con­tin­ued,” Francesca Minosi, of the Lanciano Elisa farm in the province of Lecce, said.

“Our expe­ri­ence began about four years ago, when some of our olive trees showed symp­toms of des­ic­ca­tion,” Minosi, who man­ages olive groves com­posed of Ogliarola salentina and Cellina di Nardò vari­eties, said.

“While look­ing for solu­tions to this new dis­ease and dis­cussing them with other olive grow­ers and peo­ple in the sec­tor, we found this set of prac­tices which we first decided to apply to 200 trees,” she added.

After a year of treat­ment, Minosi met the researchers and agreed to allow them to mon­i­tor and col­lect data from her orchards.

“The symp­toms of des­ic­ca­tion prac­ti­cally dis­ap­peared, shortly after we started,” she said.

Over the years, espe­cially in late spring or early sum­mer, Minosi had observed spo­radic episodes of des­ic­ca­tion in her groves. However, she stopped notic­ing them after the appli­ca­tion of the organic com­pound.

“Our olive trees have man­aged to recover well, and we have always remained in pro­duc­tion with good fig­ures, in terms of both quan­tity and qual­ity,” she added.

Since the ini­tial trial, she has extended the pro­to­col to all her groves – a total of 1,200 trees.

“We did not want to explant our cen­te­nary trees because, at the time, nobody was cer­tain of what would hap­pen,” Minosi said. ​“Eradicating and implant­ing them seemed too haz­ardous. We felt this was the most appro­pri­ate way to han­dle the emer­gency.”

The researchers point out that the use of the com­pound is aimed at grow­ers with medium and small oper­a­tions who, for var­i­ous rea­sons such as tra­di­tional har­vest­ing or logis­ti­cal dif­fi­cul­ties, can­not man­age replace­ment oper­a­tions in their olive groves.

In the provinces of Lecce and Taranto, there are two dis­tinct groups of olive farm­ers test­ing out the researchers’ com­pound: a group of farm­ers enter­ing their fourth and fifth year of the appli­ca­tion and another group enter­ing their third year.

“They all reached an aver­age annual pro­duc­tion, depend­ing on the har­vest, between four and six tons per hectare (1.6 to 2.4 tons per acre), meet­ing nor­mal pro­duc­tion stan­dards,” Scortichini said. ​“Moreover, all these farm­ers are pre­serv­ing the his­tor­i­cal, cul­tural, and land­scape her­itage, as well as the unique germplasm of Salento.”

As Southern Italy enters the full throes of spring, farm­ers are mow­ing the grass in their groves in accor­dance with the low-envi­ron­men­tal-impact agro­nomic and physi­atric phy­tosan­i­tary mea­sures rec­om­mended by the Puglia regional gov­ern­ment.

“The most effec­tive tool to com­bat the spread of Xylella on the regional ter­ri­tory is to pre­vent its spread over short and medium dis­tances, and to do this, it is very impor­tant to elim­i­nate vec­tors,” the regional author­ity said. ​“April is the most strate­gic month for the fight against vec­tors, since the insect is still in its juve­nile stage, sta­tic and vul­ner­a­ble, and eas­ily local­ized on wild plants.”

“In this month, it is essen­tial to elim­i­nate the spon­ta­neous flora on which the nymphs live, with plow­ing or shred­ding, to sig­nif­i­cantly reduce the juve­nile pop­u­la­tion of the vec­tors present in the fields and in par­tic­u­lar in the olive groves,” the author­ity added.

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