Growth Retardation Activity of Paclobutrazol on Chrysanthemum

Abstract Height of potted chrysanthemums ( Chrysanthemum × morifolium Ramat.) was effectively controlled by soil drench applications of paclobutrazol [ICI-PP-333 = (2RS, 3RS)-l-(4-chlorophenyl)-4,4-dimethyl-2-l,2,4-triazol-l-yl-pentan-3-ol]. While response to the chemical depended on normal flowering height of each cultivar, rates of 0.125–0.750 mg ai/15-cm pot were effective on the tall- and medium-height cultivars tested. Aqueous foliar sprays were ineffective in controlling plant height. Foliar sprays of paclobutrazol mixed in 15% ethanol caused significant height reduction of chrysanthemum. Foliar sprays were not as effective as soil drench applications for controlling growth.