Chemical Growth Retardants for Height Control of Pot Asters

Abstract

, then averaged), height (pot rim to the top of the plant), and days from potting to flowering were recorded. Data were tested using analy- sis of variance by general linear model proce- dures (SAS Institute, Cary, N.C.). Signifi- cantly different means were separated by least significant differences at P ≤ 0.05. Foliar applications of daminozide at 5000 mgliter -1 had the greatest effect on plant height for both cultivars, with plant height 29% and 24% shorter, respectively, than the nontreated plants (Table 1). With paclobutrazol at 160 mgliter -1 , plants also were 22% and 14% shorter than nontreated plants for 'Butterfly Blue' and 'Purple Monarch', respectively. The effectiveness of uniconazole varied by culti- var, with a rate of ≥10 mgliter -1 controlling plant height of 'Purple Monarch' by ≥10%. Asters (Aster novi-belgii L.) are hardy pe- rennials that can reach ≈140 cm tall (Bailey and Bailey, 1976) and bloom naturally in the late summer and fall. For greenhouse- produced pot asters, plants receive long days for 3 to 4 weeks after potting to promote vegetative development and increase plant size. During the vegetative phase, the plants may become elongated and disproportional to pot size, making them less attractive to the consumer. The only recommendation avail- able to growers to control plant height is to apply several foliar sprays of butanedioic acid mono (2,2-dimethylhydrazide) (daminozide) at 1000 to 5000 mgliter -1