Articles
THE USE OF PLANT GROWTH REGULATORS TO PROMOTE BRANCHING AND TO RESTRICT SHOOT EXTENSION AND AXILLARY BUD DEVELOPMENT IN POT CHRYSANTHEMUMS (C. MORIFOLIUM RAMAT)
Bright Golden Anne when applied at 4000 or 8000 mg active ingredient/litre to the apical region of plants within a few days of planting.
The compound did not always prevent the development of the terminal bud, but reduced apical dominance sufficiently to permit the lateral shoots to develop normally.
Applied at this early stage UBI-P293 had no effect on lateral stem extension.
A single foliar spray of a new quaternary ammonium growth retardant, piproctanyl bromide, could adequately shorten stems when given only 2 days after manual ‘pinching’. Daminozide was more effective if sprayed later, when the lateral shoots were 2–3 cm long but, even so, one application did not sufficiently control the height of tall cultivars under summer conditions.
When sprayed at the latter stage of growth piproctanyl bromide causes 2–5 days more delay in flowering than daminozide for a similar degree of stem retardation, but the earlier application of the new chemical reduced this difference by 1–2 days.
Only daminozide caused a loss of flower colour in cv.
Regal Anne.
UBI-P293, at low concentrations, was also highly active as a retardant in a single application and, if the concentration was raised, it inhibited the further development of 50% or more of the axillary inflorescences.
However, in order to achieve both height control and a substantial ‘disbudding’ effect in one operation the concentration of the foliar spray and the timing of its application are fairly critical.
Thus, high concentrations or early applications not only produce unnecessarily short stems and leaf mottling but also severely retard the development of terminal inflorescences.