Ethephon concentration and timing effects on thinning Winter Cole pears

Ethephon was tested as a thinner for mature Winter Cole pear trees in a trial conducted at Nubeena in south-eastem Tasmania during the 1988-89 season. Trees were treated with ethephon (0, 50, 100, 200 or 400 mg/L) at full bloom or 11 days after full bloom, or at both times. Models were fitted to the response variables of numbers of fruit per cm2 limb cross-sectional area and per 100 blossom clusters. The full bloom sprays removed significantly (P<0.05) more fruit than the later sprays. Spraying at both times gave an unexpected intermediate result between the full bloom and the later sprays. Although most treatments produced more thinning than the control, only the higher concentrations of ethephon applied at full bloom or at both times were close to achieving the required thinning results. It was concluded that although ethephon applied at full bloom is a feasible thinner for pears, further work is needed before accurate recommendations on concentration or time of application can be made. © 1991 CSIRO.