Control of Mal secco disease in lemon by drip irrigation with fungicide

Abstract

Mal secco disease of citrus is caused by the mitosporic ascomycete fungus Plenodomus tracheiphilus (formerly Phoma tracheiphila [Petri]). Mal secco is a highly destructive vascular disease of lemon and other citrus which is presently confined to the Mediterranean basin and has a marked economic impact on the citrus industry. The fungal pathogen infects the host tree by penetrating through wounds in the roots or canopy. Infection spreads quickly into the main branches and trunk and tree mortality usually ensues. The most typical symptoms are veinal chlorosis, leaf wilt, red discoloration of the xylem and dieback of twigs and branches. Current accepted control of the disease is mainly by sanitation of infected wood, and copper application during the winter to prevent germinating spores from infecting the plant. No effective chemical control for this disease has been reported. We present a drip-irrigation protocol to protect trees and control the disease in which we apply 250 g/ha of the triazole fungicide flutriafol five times a year. Progression of disease symptoms in the treated trees was inhibited by up to 81% compared to the untreated control, thereby significantly shortening the sanitation process and making it less costly than in untreated trees. Moreover, disease symptoms became less severe as the duration of treatment increased. We have treated orchards for 3 years, and present an effective commercial protocol for the growers which will help them control Mal secco disease.