Effect of paclobutrazol, uniconazole and flurprimidol applied as a substrate drench or by subirrigation on growth of Monarda didyma and Buddleia davidii

Scope and Method of Study: Plant growth regulator use in nursery production of Bee Balm (Monarda didyma 'Marshall's Delight') and Butterfly Bush (Buddleia davidii 'Pink Delight') was the focus of this study. paclobutrazol ((2RS,3RS)-1-(4-chlorophenyl)-4,-4dimethyl-2-(1,2,4-trizol-1-yl)pentin-3-ol), uniconazole ((E)-1-(4-chlorophenyl)-4,-4-dimethyl-2-(1,2,4-trizol-1-yl)pentin-3-ol), and flurprimidol ((alpha-(1-methylethyl)-alpha-[4-(trifluoromethoxy)phenyl]-5-pyrimidine-methanol)) were applied as a substrate drench applied or through subsurface irrigation applied in a saucer placed under each plant to control plant growth. Three trials were conducted.;Findings and Conclusions: The spring greenhouse Monarda didyma study showed height was the only measured variable that differed among treatments. The effectiveness of the PGRs in reducing plant growth was increased with subirrigation compared to plants that received no PGR during subirrigation. Plants that received no plant growth regulator were taller than those receiving any of the three plant growth regulators. The quality of the plants did not differ among control, paclobutrazol, and flurprimidol treatments. Plants treated with uniconazole had the poorest quality. The results of the spring trial showed paclobutrazol applied by subirrigation gave the best height and width control while preserving plant quality throughout production.;The summer outdoor and fall greenhouse Monarda didyma studies showed that among the three chemicals there was a gradual decrease among height and width of the plants as the rate of application increased for both substrate drench and subirrigation methods of application.;During the spring study the PGRs applied as a continuous treatment through substrate drench or by subirrigation were statistically significant by height for Buddleia davidii 'Pink Delight'.