EFFECTS OF PLOUGHING IN AND REMOVING LITTER LEAVES FROM THE GROUND ON THE DEVELOPMENT OF SCAB EPIDEMICS IN AN ORGANIC APPLE ORCHARD

Summary

Ascospores produced on scabbed leaves in the leaf litter are the main source of scab primary inoculum, causing scab infections in apple orchards. The purpose of this experiment, carried out during two years in a commercial organic orchard, was to assess the effect of combining leaf removal from the alleys and leaf ploughing in within the row, on scab primary inoculum and therefore on scab epidemics. Scab lesions were monitored on leaves and fruits by assessing scab incidence and scab severity. In 2003, scab severity was monitored at different distances from the unremoved leaf area, in order to estimate ascospore spreading. At fruit harvest, along two years with low (2003) and high (2004) levels of scab development, the leaf litter ploughing in / removal method reduced fruit scab incidence by 82% and 54% respectively, and fruit scab severity by 74% and 68%. Measures of ascospore spreading indicated that the spreading was not important beyond 20 meters from the unremoved leaf area.