Sources of Botrytis cinerea inoculum for flower infection in blackcurrants in New Zealand

Botrytis cinerea is a major disease of blackcurrants causing premature flower and fruit drop in New Zealand. Because of the risk of fungicide residue from conventional methods, there is a need for the development of non-chemical control strategies as part of a sustainable disease control programme. Potential sources of Botrytis cinerea inoculum for infection of blackcurrant flowers were sampled in five blackcurrant properties in the South Island of New Zealand during dormancy and spring of 2006 and 2007. Tissues investigated were necrotic debris immediately beneath the plant, necrotic growing tips of 1-year-old canes, dead cane of previous seasons growth still attached to the base of the plant, canes damaged by harvesting or pruning, and canes damaged by currant clearwing (Synanthedon tipuliformis). The mean number of each tissue type within a plant varied considerably, both within a property and between different properties. Necrotic debris immediately beneath the plant and necrotic cane tips were shown to be the main sources of inoculum. Knowledge of the main sources of inoculum is an important first step towards the development of new, non-chemical control strategies, which are discussed in this context.