Incidence ofVenturia inaequalison apple fruit during the second half of the season under different fungicide and weather regimes

Abstract

The incidence of apple scab (Venturia inaequalis) on apple fruit was estimated from December to March in orchards with different levels of leaf and fruit scab and under different fungicide programs. Twenty orchards were monitored at Batlow, NSW, Australia from 1990 to 1993. Moderate levels of primary infection in the 1990/91 season resulted in levels of leaf scab in December/ January, which varied from 0 to 6.2% (mean 0.8%), and fruit scab in December from 0 to 7.1% (mean 0.9%). Fruit scab incidence measured in March was 0.4% (after the normal practice of removal of fruit to increase remaining fruit size). A mean of 1.6 fungicide sprays were applied from January to March, with a range of 0-7 sprays. It is likely that infection criteria would have been met on three occasions during December-March. No significant increase of scab occurred in seven orchards where no fungicides were applied over this period. In the 1991/92 season, a dry spring resulted in five infection periods, four of which were low severity. No leaf scab was detected in December. A mean of 0.02% fruit infection (range 0-0.2%) was detected in December. The mean level of fruit infection was H94012