MODELING THE EFFECTS OF TIMING AND RATES OF APPLICATION OF BENZYLADENINE AS A SECONDARY THINNER OF FUJI APPLE AFTER ETHEPHON

A trial on 'Fuji' apples at the Grove Research Station in southern Tasmania during the 1991/92 season studied the thinning effect and interactions between ethephon and benzyladenine (BA) when BA was applied as a secondary thinner after a full bloom (FB) application of ethephon. The spray treatments were a factorial combination of eight application times of BA (11, 13,15,17,19,21,23 or 25 days after full bloom (AFB)) with ten concentrations (20, 40, 60, 80, 100, 120, 140, 160, 180 or 200 mg l-1). An unsprayed control and an ethephon control were included. Target thinning results were achieved 19-23 d AFB with concentrations of 140-160 mg l-1. A corollary of this successful thinning was an increase in fruit weight and size. Return bloom was improved significantly where thinning was successful. There was no effect on fruit firmness, soluble solids or lateral branching. Drawbacks were an increase in the incidence of russet and a reduction in pip number at the optimum thinning times and concentrations.