Chemical and mechanical methods to reduce leader growth in fraser fir

by 1982- Aspinwall, Martha Elizabeth

ASPINWALL, MARTHA ELIZABETH. Chemical and Mechanical Methods to Reduce Leader Growth in Fraser fir. (Under the direction of Drs. John Frampton and Gary Blank) The purpose of this research was to provide American Christmas tree growers with alternative methods of reducing leader growth compared to the traditional cultural practice of shearing. Separate experiments involving the use of a mechanical tool, the Top-Stop Nipper (TSN), and the application of naphthaleneacetic acid (NAA) were conducted in Avery County, North Carolina on Fraser fir [Abies fraseri (Pursh) Poir.] during the spring and summer of 2005 and 2006. The Top-Stop Nipper, a four-bladed hand-held tool, placed incisions (nips) on the previous year’s leader to reduce the amount of photosynthate being transported to the developing leader. The treatments for the 2005 experiment consisted of a control (0 nips, nonsheared), one, two, three, or four nips at each of three stages of leader elongation [pre-budbreak, 2-3 cm, and 6-9 cm]. For the 2006 experiment, a regression model, based on an apical bud volume index from the 2005 experiment, was used to predict the number of nips to apply to each leader to yield a target length of 25 to 36 cm. The treatments included control trees (0 nips, nonsheared) and one to seven nips per leader. Treatments were applied in early May as buds began to swell and elongate. In 2005, a chemical experiment was conducted to evaluate the effectiveness of the potassium salt form of 1-naphthalene acetic acid (NAA) at reducing leader growth in Fraser fir. NAA was dissolved in water and applied using the Danish- made Easy Roller. Treatments were applied to leaders at concentrations of 0 to 70 ppm in 10 ppm increments at three stages of leader elongation (6-9 cm, 12-18 cm, and 24-36 cm). In 2006, two methods of application, the Danish Easy Roller and the German Sprühsystem, were tested to evaluate the effectiveness of ethyl 1- naphthaleneacetic acid (NAA) at reducing leader growth of Fraser fir Christmas trees. A commercial product, Sucker-Stopper RTU (SS-RTU), which contains 1.15% ethyl 1-naphthaleneacetic acid was applied to leaders at concentrations of 0 to 500 ml/L commencing when leaders were 8 to 15 cm long. Results for the 2005 TSN experiment included a significant reduction in leader elongation; the percentage of leaders that were within the target range of 20 to 36 cm increased from 18% for the control (no nips) to 46% with four nips. In 2006, when the number of nips increased with increasing bud volume, leader growth was about the same among all TSN treatments. Bud density on the 2006 leader increased with the number of nips applied to the 2005 leader. The TSN might be a useful alternative to standard shearing for growers who intend to produce dense trees with minimal shearing or for growers who leave longer leaders to produce a more open “European-style” tree during a shorter rotation time. In 2005, the application of the potassium salt form of NAA had no effect on leader elongation, which may be due to the form of NAA used in the experiment. In 2006, as the concentration increased, leader elongation decreased. The Easy Roller more effectively reduced leader growth, but leader mortality was unacceptable at concentrations ?120 ml/L. Although less effective than the Easy Roller in reducing leader growth, the Sprühsystem caused negligible mortality of leaders. Applying 40 ml/L with the Easy Roller yielded about 50% of leaders with target lengths of 20 to 36 cm, with little mortality. The Sprühsystem gave similar results at 250 ml/L. NAA might be useful for producing dense trees with minimal shearing, or for producing more natural, open trees with shorter rotations. Chemical and Mechanical Methods to Reduce Leader Growth in Fraser Fir by Martha Elizabeth Aspinwall A thesis submitted to the Graduate Faculty of North Carolina State University in partial fulfillment of the requirements for the Degree of Master of Science Natural Resources Raleigh, NC 2007