Four statements questioning the EU control strategy against Xylella fastidiosa

Abstract

This opinion addresses questions concerning the EU control strategy against Xylella fastidiosa: i) factors affecting symptom expression and spread of X. fastidiosa; ii) the aetiology of the CoDiRO (Complesso del Disseccamento Rapido dell’Olivo) disease; iii) host plant removal as an option for containment or eradication; and iv) secondary effects of pesticides. Xylella fastidiosa subsp. pauca was shown to be the causal agent of the CoDiRO disease of olives by recent biological assays fulfilling Koch’s postulates. Symptoms in X. fastidiosa infected plants develop because of wilting from water stress induced by bacteria clogging the xylem vessels. Therefore, interventions supporting vigorous growth and development of the plant may improve its health status, its resilience, prolong its productive phase and extend the symptomless phase of the disease. The Panel considers removal of infected plants, in a system-based approach, as the only option to prevent further spread of the pathogen to new areas. In the outer strip of the containment area bordering the buffer zone, removal of infected plants and stringent monitoring can be effective in preventing pathogen spread into the buffer zone. In areas of recent introduction, such as new outbreaks in the buffer zone, the stringent removal of both infected plants and all host plants irrespective of their health status within a radius, as described in current EU legislation, can be effective in reducing pathogen spread, when rigorously administered and new infections are detected in time. Finally, the reduction of vector populations by application of chemical or biological means, mechanical treatments, or other sustainable methods, can have effects in slowing down the pathogen spread. Concerning the use of pesticides, there is currently no evidence of negative effects of such treatments on the interaction of X. fastidiosa with infected olive trees, the severity of symptoms and the outcome of the infection.