Juanita Popenoe

Branch induction on apple nursery trees: Effects of growth regulators and defoliation

Abstract One‐year‐old apple (Malus domestica Borkh.) nursery trees of several cultivars on MM 106 and M 9a rootstock were sprayed once in early summer with benzyladenine (B A) followed by one, two, or three applications of gibberellin (GA4+7) either in 1989 or in 1990. In both years GA4+7applied at the same time or 2 weeks after a B A spray produced more branches and more total growth than controls. In 1990, but not 1989, GA4+7 applied 2 weeks after BA stimulated more branches and more total branch length than when these chemicals were applied together. In 1990 multiple applications of GA4+7 beginning 18 days after B A sprays induced the longest branches, most total branch growth, and greatest branch crotch angles than applications involving a single GA4+7 plus B A spray. In addition in 1989, immature leaves were removed immediately beneath the growing tip on the main stem (LR) once in early summer and sprayed with or without GA4+72 weeks later. Leaf removal treatments did not affect branching.