Orchard sanitation as a management approach to control apple scab in South African apple orchards

Abstract: South African apple producers use 6-15 fungicide sprays per season to control applescab, caused by Venturia inaequalis (Cke.) Wint. However, despite the availability and use ofeffective fungicides, severe losses to scab are regularly sustained in South African appleorchards. The global trend towards integrated management of scab and reducing reliance onagricultural chemicals, as well as the urgent need for expertise on scab in South Africa, promptedthe initiation of this project. The aim of this project is to compare the efficacy of sanitationstrategies with conventional chemical strategies in reducing scab incidence and severity in SouthAfrican apple orchards. This is the first commercial-scale study on the use of orchard sanitationto control scab in South Africa. Using a randomized block design, six treatments were replicatedthree times, with three orchards each acting as a block. The treatments were: leaf removal; leafshredding; postharvest urea sprays at 70% and 100% leaf drop, an integrated treatment thatcombined leaf-shredding and urea; a non-sanitized/non-sprayed negative control, and a nonsanitizedpositive control sprayed according to guidelines in a standard scab fungicideprogramme. Treatment effect on fruit and leaf incidence and severity were not statisticallydifferent from controls, with the exception of leaf shredding, which was 15% lower than in thenegative control in November 2010. Why treatments were not more effective in reducing scabincidence and severity is discussed.