Fruit and Hormones Influence Flowering of Apple. II. Effects of Hormones

Combination postbloom sprays of BA at 50 mg·liter -1 and daminozide at 2000 mg·liter -1 were made to limbs of `Early McIntosh' apple (Malus domestics Borkh.) where all of the flowers were either removed before full bloom or allowed to remain. BA and fruit removal increased return bloom, whereas daminozide bad no effect. No treatment had a consistent effect on spur leaf area. Repeat sprays of GA 4+7 to `Delicious' apple trees at full bloom (FB) +5, FB + 14, and FB +22 days reduced appendage development and flower bud formation on spurs. One spray of GA d+7 at 150 mg·liter -1 at FB +42 days reduced appendage formation and the percentage of flowering spurs but not as effectively as earlier repeat sprays of GA 4+7 at 50 mg·liter -1 When BA at 150 mg·liter -1 was combined with the GA at FB +42 days, appendage formation was increased but the reduction in flowering was not reversed. One BA spray at 50 mg·liter -1 at FB +22 days to `McIntosh' trees increased the number of appendages formed in spurs, but return bloom was not influenced. Chemical names used: (N -phenylmethyl) -1 H -purine-6-amine (BA); butanedioic acid mono (2, 2-dimethylhydrazide) (daminozide); gibberellins A 4 and A 7 (GA 4+7 ).