Effects of pruning and plant growth regulators on branching and growth of azalea

Abstract

Many woody plants do not branch well during nursery container production. Various plant growth regulators (PGRs) have been used to promote branching. The objective of this study was to evaluate the effects of dikegulac sodium (Atrimmec) and cyclanalide (Tiberon 2.8SC) in combination with or without pruning on branching and growth of two cultivars of azalea (Rhododendron sp.). For azalea 'Midnight Flare', Atrimmec at 3100 mg L-1 applied twice and Tiberon 2.8SC at 100 mg L-1 applied twice or 200 mg L-1 applied once significantly increased branching in 8 weeks after the initial treatment (WAIT), regardless of pruning treatment. However, by 20 and 30 WAIT, there were no significant differences on the number of shoots per plant among all the treatments. For azalea 'Katherine Alison', at 8 and 20 WAIT, plants which received pruning and were treated with two applications of Atrimmec at 3100 mg L-1 had significantly more shoots than plants that did not receive pruning but were treated with one application of Atrimmec at 3100 mg L-1. By 30 WAIT, there were no significant differences between the number of shoots per plant among all the treatments. No phytotoxicity was observed. For both azalea cultivars, at 8 WAIT, plants which received pruning had a significantly lower plant growth index (PGI) than plants that did not receive pruning. At 20 and 30 WAIT, pruning generally did not have a significant effect on PGI.