Effect of fungicidal treatments on severity and incidence of elsinoe leaf spot of apple

Abstract

The effectiveness of seven products suitable for organic pipfruit orchards on reducing incidence and severity of Elsinoe leaf spot was examined Novel products potassium carbonate and a saponincontaining Yucca schidigera extract were first tested at different concentrations in the laboratory using poison plates and poison slides Increasing concentrations of both products resulted in decreasing Elsinoe piri conidium germination on agar plates and glass slides as well as decreasing size of germination tubes Conidium germination was significantly reduced compared with controls when the concentration of potassium carbonate or the Y schidigera product was 01 or 25 respectively or higher In a glasshouse different rates of products were applied to potted Royal Gala trees prior to inoculation with conidia of E piri (210⁵ conidia/ml) Disease incidence and severity were significantly reduced when trees were treated with lime sulphur (1 and 2) a low concentration of products containing Y schidigera extract (25) copper hydroxide (0009 and 0019 copper) sulphur (016) or a low concentration of potassium carbonate (05) compared with the control However a different saponincontaining product and high concentrations of potassium carbonate (1) and a Y schidigeracontaining product (5) did not reduce disease incidence or severity In fact 1 potassium carbonate significantly increased disease severity compared with the control