Influence of growth retardants on growth and flower bud formation in rhododendron and azalea

Plants of ‘Catawbiense Boursault’ and ‘Eskimo’ rhododendrons or ‘Cannon’s Double’ and ‘Kilian’ azalea grown in 4 l containers were treated twice with chlormequat (2000, 4000 and 8000 mg · dm-3), trinexapac-ethyl (50, 100, 200, 400 mg · dm-3), daminozide (2500, 5000, 7500 mg · dm-3), proxeadione calcium (75, 150, 300 mg · dm-1) and once with paclobutrazol (50, 100, 200, 400 mg · dm-3). Shoot length of the subsequent growth flush following the treatments decreased with increasing rates of the growth retardants. The number of flower buds per plant increased with increasing rates of pacloburazol, chlormequat and daminozide. Prohexadione calcium was less effective in flower bud initiation and the worst results were obtained with trinexapac-ethyl.