Elimination of summer fungicide sprays for apple scab (Venturia inaequalis) management in Uruguay

Apple scab caused by Venturia inaequalis is the most important disease of apple in Uruguay. Under conventional management an average of 14-16 fungicide sprays are used each season to control this disease. In this work, the elimination of fungicide sprays for apple scab control after mid-December was evaluated during two seasons in three commercial apple orchards planted with cultivars of Red Delicious, the main apple produced in Uruguay. This finding was based on the ontogenic resistance which implies that the susceptibility to apple scab of leaves and fruits decreases with the ageing of the tissues. Increments of scabbed leaves happened during the summer and fall in all orchards evaluated, but this increase happened in both treatments, with or without fungicide applications during the summer. Instead, none of the orchards evaluated showed increases of apple scab lesions on fruit after December 15th. This finding suggests that it is feasible to reduce up to 30% of fungicide sprays to control apple scab in apple fruit that are harvested from January (like cultivars of Gala) to March (like cultivars of Red Delicious) in Uruguay.