The Effect of Leaf Shredding on Apple Scab in South African Orchards

Abstract

The South African apple industry currently relies entirely on chemical fungicides to control apple scab (Venturia inaequalis). In this study, the effectiveness of sanitation strategies in reducing scab incidence and severity in South African orchards was evaluated. Over three seasons, leaf shredding with no fungicide sprays was tested against a nonsprayed, nonshredded negative control, a positive control that followed a commercial fungicide program, and a combined treatment of a commercial fungicide program with leaf shredding. Two treatment replicates were applied in a randomized block design in each of two orchards. Scab incidence and severity on fruit and leaves were assessed weekly from green-tip until fruit-set in the following spring. Pooled data from the 3 years revealed that fruit scab incidence and severity and leaf scab severity (51, 55, and 39%, respectively, P < 0.05) and leaf scab incidence (33%, P < 0.1) were significantly lower in the leaf-shredding treatment than in the negative control. This is the first study to evaluate the effect of leaf shredding in reducing scab in South African orchards. Results indicate that this treatment is highly effective and should be integrated into scab management strategies in future, but should be customized to suit South African orchard conditions.