Cupric hydroxide mixed with sulphur gave good disease control but the fruit still showed russet. This is thought to be due to the copper in the mixture. Therefore, if fruit finish is an important consideration, slaked lime may be a better alternative. Slaked lime did not appear to affect fruit colour although it did produce a white chalky deposit on the apple surface. This deposit could potentially be wiped off at harvest or removed in the water dump at the packhouse.
Slaked lime degrades to calcium carbonate in the air and is considered environmentally safe.
Both these compounds are relatively in-expensive compared to a standard synthetic fungicides. In addition, a further set of treatments alternated a sulphur spray with each of the compounds to give ten fungicide applications during the primary infection season. After the 12 December, all plots received a standard programme of fortnightly cupric hydroxide and sulphur until harvest. On the 6 December, the levels of black spot and powdery mildew were assessed on the leaves, and black spot and russet were assessed on the fruit. The trials at Winchmore were to determine the effects of different concentrations of cupric hydroxide and slaked lime.