Naphthaleneacetic acid reduces leader growth of fraser fir Christmas trees.

Two methods of application, the Danish Easy Roller and the German Spruhsystem, were tested to evaluate the effectiveness of naphthaleneacetic acid (NAA) at reducing leader growth (tips of primary axes) of fraser fir [Abies fraseri (Pursh) Poir.] Christmas trees. A commercial product, Sucker-Stopper RTU (1.15% ethyl 1-NAA), was applied to leaders at concentrations of 0 to 500 mL.L-1 when leaders were 8 to 15 cm long. As the concentration increased, leader elongation decreased. The Easy Roller reduced leader growth the most, but leader mortality was unacceptable at concentrations 20 mL.L-1 or greater. Although less effective than the Easy Roller, the Spruhsystem caused negligible mortality, of leaders. Applying 40 mL.L-1 with the Easy Roller yielded approximate to 50% of leaders with target lengths of 20 to 36 cm with little mortality. The Spruhsystem gave similar results at 250 mL.L-1. NAA might be useful for producing dense trees with minimal shearing or for producing more natural, open trees during shorter rotations.