INFLUENCE OF PINE BARK ON THE EFFICACY OF DIFFERENT GROWTH-RETARDANTSAPPLIED AS A DRENCH

Dendranthema xgrandiflorum (Ramat.) were grown in either a peat-based or pine bark-based medium and drenched with growth retardants at a ran ge of concentrations to generate dose : response curves. The effect of ancymidol, paclobutrazol, and uniconazole on stem elongation was less in the pine bark-based than in the peat-based medium. Generally, the concentrations required to achieve the same response were 3- to 4-fold as high in the pine bark-based medium as in the peat-based medium. Ho wever, chlormequat was slightly more active in the pine bark-based med ium than in the peat-based medium. Chemical names used: (4-methoxyphen yl)-5-pyrimidinemehtanol(ancymidol); ]-alpha-(1,1-dimethyl)-1H-1,2,4-t riazole-1-ethanol (paclobutrazol); -dimethyl-,2-(1H-1,2,4-triazol-1-yl )pent-1-en-3-ol (uniconazole); 2-chloroethyltrimethglammonium chloride (chlormequat).