Chemical Growth Retardant Application to Tuberous-rooted Dahlias

Abstract

were fertilized at each watering (mgliter -1 ) with 201 N, 46 P, and 200 K. Greenhouse day/ night set points were 24/18C. The plants were grown under natural daylength. Eight plant growth retardant (PGR) media drench treat- ments (mg a.i./pot) were applied 11 days after potting at 118 ml per pot: ancymidol, 1.5 and 2.0; paclobutrazol, 0.24, 0.47, 0.95, and 1.9; uniconazole, 0.24 and 0.47; plus a nontreated control. A completely randomized design of 10 single-plant replications was used. When the first inflorescence opened, the number of days from potting until flowering was re- corded. When 90% of the plants had an open inflorescence (16 May for 'Red Pigmy' and 2 June for 'Golden Emblem'), leaf canopy height measured from the pot rim to the top of the foliage, inflorescence height above the foli- In adapting tuberous-rooted dahlia (Dahlia variabilis Willd.) plants for greenhouse con- tainer production, they are generally dispro- portionately large relative to the container, making them less attractive to consumers. DeHertogh and Blakely (1976) recommended applying soil drenches of α-cyclopropyl-α- (4-methoxyphenyl)-5-pyrimidinemethanol (ancymidol) at 0.25 to 2.0 mg a.i./pot, 10 to 14 days after potting the tubers for height control. Soil drenches of chlormequat (270 and 540 mg a.i.) and foliar sprays of butanedioic acid mono(2,2-dimethylhydrazide) (daminozide) (2500 and 5000 mgliter -1 ) were not effective in controlling dahlia height (DeHertogh and Blakely, 1976). Foliar sprays of chlormequat at 1000, 2000, and 3000 mgliter -1 had the greatest effect on plant height for dahlias grown in the field for cut flowers, with a final height of 66% of the control (Gowda et al., 1991). Foliar sprays (10 to 80 mgliter -1 ) or drenches