An Integrated Approach for Reducing Fungicide Sprays Against Scab in Organic Apple Orchards

Abstract: The aim of this study was to evaluate scab control efficacy in integrated approaches of i) three sanitation treatments (fallen leaf removal combined with winter pruning and non-sanitized control), ii) three onsets of first fungicide sprays (dormant bud, early tight cluster and pink bud stage), and iii) three final dates for finishing fungicide programs (mid-July, mid-August and mid-September) in an organic apple orchard on a moderately scab susceptible cultivar, Jonathan. A delay in the onset of first spray until pink bud stage resulted in higher scab incidences on both leaves (16-21%) and fruits (13-15%) compared with the non-delayed spray treatments (5-8% and 6-9%, respectively). Final leaf and fruit scab incidences increased significantly when sprays were omitted after mid-July compared to spray treatments finished at mid-August or mid-September. A combination of leaf removal with pruning resulted in lower scab incidence (5-12%) compared with the non-sanitized plots (7-15%) when spray treatments were finished at mid-August or mid-September. Results on cv. Jonathan suggested that scab sprays could only be omitted before early tight cluster and after mid-August if leaf removal and pruning was applied.