Improving fruit set on young red ‘Delicious’ apple trees using autumn sprays of paclobutrazol and ethephon

SummaryYoung, vigorous red ‘Delicious’ apple trees were treated in the autumn of their second year with sprays of paclobutrazol and ethephon. Sprays of paclobutrazol were applied in mid-February, mid-March and mid-April 1989 at 0, 50, 100 or 200 mg l-1. Other trees were sprayed with ethephon in mid-March at 200 mg l-1 with paclobutrazol at 0, 50, 100 or 200 mg I“1. Blossoming in the spring of 1989 showed no consistent effects of autumn plant growth regulator (PGR) treatments. However, PGRs did affect fruit set in these trees. Although no significant differences occurred between any of the paclobutrazol concentrations, or timing treatments, treated trees all yielded more than the control ones. Where ethephon was used with paclobutrazol, fruit set was similar to that after paclobutrazol alone, except when paclobutrazol was used at 100 mg l-1, where the highest fruit set was achieved. Ethephon alone, while promoting better set than the control was not as effective as when combined with paclobutrazol.