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New Zealand Plant Protection 63 (2010): 279

Calcium chloride against black spot on apples

K.S.H. Boyd-Wilson, R.C. Butler and M. Walter

ABSTRACT

Calcium chloride, which is classified as "generally recognised as safe" (GRAS) under the Agricultural Compounds and Veterinary Medicines Regulations 2001, has potential for use in an organic apple production system against black spot (Venturia inaequalis). The effectiveness of calcium chloride on control of black spot was evaluated in a field trial over the 2007/2008 growing season. Calcium chloride was applied 10 times over the season at the commercially-recommended rate of 0.33 kg product/100 litres or at 2 kg/100 litres (the latter treatment was halved after two applications due to foliar damage). At harvest, fruit treated with the high rate of calcium chloride had a lower disease incidence of 41% than the water control, which had 97% incidence (P<0.001). The number of lesions on fruit treated with the high rate of calcium chloride was 10% of that of the water-treated fruit (P<0.05). The incidence of black spot on leaves was assessed three times during the season. The incidence was lower (P<0.001) for the high rate calcium chloride treatment at all three assessments.

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