A strategy for reducing russet in Red Fuji apples while maintaining control of black spot (Venturia inaequalis)

Abstract

A trial at the Grove Research Station in southern Tasmania examined methods of protection against black spot and the effect of these treatments on russeting of Red Fuji apples. An untreated control was compared with sprays of cupric hydroxide (wettable powder and dry flowable forms, 2.5 g/L) and copper oxychloride (4.0 g/L), and with dithianon (wettable powder 5 g/L, or suspension concentrate 5.0 or 7.5 gL). All sprays were applied at greentip, and dithianon was also applied at 10-day intervals for 5 sprays (spring program). Copper treatments were followed, or not, by a spring program of thiram, and all treatments were with or without a following summer program of thiram. Control of black spot (95% fruit with no spot) was not achieved with copper sprays at greentip alone, although control was better than on the unsprayed treatment. All dithianon programs, and cupric hydroxide sprays followed by thiram, controlled black spot. No difference was found between formulations for either cupric hydroxide or dithianon. Copper oxychloride increased the incidence of severe russet to >50% compared with the unsprayed control (28.5%). All other treatments were satisfactory, with similar incidence of russet to the control treatment, and could be used in commercial practices.