Evaluation of growth retardants for controlling height of Geraldton Wax flowers ( Chamelaucium uncinatum Schauer.)

Abstract

Several experiments were conducted to investigate the response of Geraldton Wax ( Chamelaucium uncinatum Schauer.) to the growth regulators ancymidol, chlormequat, daminozide, dikegulac sodium and paclobutrazol, and also to determine the effect of potting media on the efficacy of chlormequat and paclobutrazol. Ancymidol applied as a compost drench was effective in controlling the height of a hybrid cultivar of C. uncinatum for 6 weeks, but did not reduce the height of a species cultivar. Daminozide applied as a foliar spray did not affect the height of either cultivar. Chlormequat and paclobutrazol applied as compost drenches were effective in controlling the height of both cultivars. Chlormequat maintained height control for 5 weeks, after which the mean daily height increment exceeded that of plants treated with paclobutrazol. Dikegulac sodium, as a foliar spray applied simultaneously with a compost drench of paclobutrazol, severely burned the foliage and delayed regrowth. Chlormequat was less effective in controlling the height of plants grown in media containing pinebark and sand or pinebark, hardwood sawdust and sand compared with media containing peat and sand or peat, rice hulls and sand. The efficacy of paclobutrazol was diminished only in the medium containing both pinebark and sawdust. Chlormequat and paclobutrazol increased the number of flowers per plant by 40 and 25%, respectively, compared with controls.