Effectiveness of Low Dose PGR Application On Acer x freemanii 'Autumn Blaze'

With increasing labor cost and plant growth regulator (PGR) cost, it is becoming increasingly difficult for growers to maintain plant (canopy) size in situations where in-ground or large container shade trees must be held over due to a lack of sale(s). This study was initiated at the request of GA growers to investigate if low-dose PGR applications could be effective in holding growth rates down in plant material that needs to be held over past its intended sale date; principally due to slow sales seen in the last 24-36 months. PGR treatments combinations in this study were based on three factors: (1) application dates (a) at dormancy as sap-rise started (March 24, 2010), (b) at bud swell but prior to bud break (April 4, 2010), and (c) at 48h post bud break  (April 7, 2010); (2) the PGR chemical including (a) Cutlass G (flurprimidol), (b) TopFlor (flurprimidol), and (c) Embark (mefluidide); (3) the application rate including (a) 10% label rate, (b) 50% label rate, (c) 100% label rate and (d) control without PGR application. Results indicated that based on the growth rate of the control treatment, Cutlass and Embark failed to significantly control growth rate of Acer x freemanii 'Autumn Blaze' regardless of application rate or application timing. TopFlor, applied as a soil drench at 10% label rate, significantly reduced season-long growth rate of Acer x freemanii 'Autumn Blaze' when applied between sap rise and bud swell. Once bud swell initiated, the 10% TopFlor rate no longer exhibited season-long reduction in growth rate. However, both 50% and 100% label rate of TopFlor showed significant control of Acer x freemanii 'Autumn Blaze' growth rate regardless of application date. These results are promising for growers that may now have a new tool in controlling growth rate in this genera at a much lower cost per unit.