Training system and tree-age affect leaf spot epidemics and tree defoliation on commercial sweet cherry cultivars

Abstract

In two 3-year studies, the effect of two training systems (free spindle versus super spindle) and two tree-age periods (4–6 versus 13–15 years) were evaluated on cherry leaf spot (CLS) epidemics and tree defoliation for 12 sweet cherry cultivars in an integrated orchard. Then, relationships among CLS infection periods, CLS incidences and percent defoliation were determined for the training systems and tree-age periods. In addition, cultivars were classified into three CLS susceptibility and three defoliation categories (low, moderate, and high). Annual CLS and defoliation incidences of individual cultivars were lower, by 0.05–10.8% and by 0.1–9.1%, respectively, on trees pruned to super spindle compared to trees pruned to free spindle, except for defoliation incidences on cultivars ‘Biggareau burlat’ and ‘Müncheberger’, where training system had no effect. The three-year means of CLS and defoliation incidences ranged from 18.0 to 70.5% and from 14.1 to 47.9%, respectively, on the 4–6 years old trees; and from 8.7 to 34.7% and 5.4–25.5%, respectively, on the 13–15 years old trees. Leaf spot infection period, CLS incidence and defoliation incidence showed strong relationship in both training systems in those years when annual CLS incidences were high. Cherry leaf spot and defoliation classification categories of some cultivars were different for the two training systems and/or for the two three-year periods. Our study demonstrated that both training system and tree-age can impact the severity of leaf spot epidemics and tree defoliation for sweet cherry genotypes showing moderate susceptibility to leaf spot.