Calcium hydroxide sprays for the control of black spot on apples -- treatment effects on fruit quality.

摘要

To reduce the number of fungicide sprays for the control of black spot Venturia inaequalis, a novel approach has been developed by the Tasmanian Department of Primary Industry and Fisheries, Tasmania, Australia. This involves the modification of theleaf surface pH, by the use of calcium hydroxide, to a level which inhibits the germination of fungal spores. Unfortunately, the foliar residue from the calcium hydroxide may reduce photosynthesis and hence, affect potential yield and fruit quality. Forthis reason, four field trials were established in two orchards (Grove and Cradoc) in Tasmania, Australia during 1995-96. The three treatments tested were an unsprayed control, four sprays of calcium hydroxide at 4 kg/100 litres during the first spray and 2 kg/100 litres on subsequent sprays, and calcium hydroxide at the same concentrations with addition of copper hydroxide at the final 2 application dates. At commercial maturity, fruits were harvested and assessed for quality. Fruit parameters measured varied between cultivars (Golden Delicious, Fuji and Red Delicious) and included yield, colour, skin strength, incidence of russet, weight, shape, firmness, ethylene production, sugars, starch, water core and alcohol insoluble solids. Calcium hydroxidealone did not affect any of the fruit quality parameters measured whilst the calcium plus copper spray increased fruit firmness by 11.6% and fruit alcohol insoluble solids by 11% in some trials. For Golden Delicious, the combined spray mixture increasedthe incidence of fruit russet by 4-fold, which is an unacceptable level. The commercial significance of these findings is that apple trees treated with calcium hydroxide for the control of black spot have similar yields and fruit quality to unsprayed trees. These findings demonstrate the crop safety of this treatment for the control of black spot on apples. The addition of copper hydroxide had some positive effects on fruit quality, however, the increase of russet limits the commercial application of this treatment.