Effect of 2,4,5-trichlorophenoxypropionic acid on setting and cropping of Packham's Triumph pear under Goulburn Valley conditions

Abstract

The effects of 2,4,5-trichlorophenoxypropionic (2,4,5-TP) acid sprays on Packham's Triumph pear fruit set and cropping were investigated. There were no favourable effects on fruit set from 2,4,5-TP at 10 p.p.m. when spray was applied at the beginning of bloom. When applied at 50 per cent bloom, sprays of 10 p.p.m. did not increase set in seasons with high natural set, but they did cause very large increases in set in seasons with low to moderate natural set. However, due to the heavy fruit load, a great proportion of the fruit remained small, so that commercial yield of the fruit from treated trees was not significantly better than from untreated controls. The beneficial effects on setting and cropping from autumn applications were obtained only with repeated sprays of 5 + 5 p.p.m. applied in March and April, but not with a single application of 5 p.p.m. in March. Fruit fertilization (seed number) was substantially reduced in some seasons and situations but not in others. Also, in years with heavy set increases some damage to blossom clusters and spurs occurred and leaf area on spurs, but not on laterals, was reduced.