Naphthaleneacetic Acid Reduces Leader Growth of Fraser Fir Christmas Trees

Abstract. Two methods of application, the Danish Easy Roller and the German Sprü hsystem, 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 mLÁL -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 mLÁL Derby, 2004a, 2004b) to produce dense trees for American consumers. Traditional shearing removes the apical bud cluster from the leader (distal end of the primary axis) and most lateral branches. Leaders are usually shortened to 20 to 50 cm, often half the original length, depending on the tree's potential for growth, its age, and consumer preferences The Christmas tree industry is driven by consumer preference. Tree shape is an important factor to consumers (NCDA&CS, 2002); %53% of American consumers favor a full tree, and 43% favor a more open tree Sucker-Stopper RTU (SS-RTU) [1.15% ethyl 1-naphthalene acetic acid (NAA); Lawn and Garden Products, Inc., Fresno, CA] is used to reduce or prevent the growth of sprouts and suckers on various woody plants. Naturally occurring auxins such as indoleacetic acid are involved in shoot elongation, cell division, flower formation, and inhibition of root growth Materials and Methods Two methods of application were used. The Easy Roller (Easy Roller; Lars B. Madsen, Langmosevej 6, 8620 Kjellerup, Denmark) has two rollers mounted parallel on the end of two metal extensions The research was conducted in the mountains of western North Carolina during Spring and Summer 2006. The three test sites-typical of fraser fir Christmas tree plantations-were 920 to 1200 m above sea level. A total of 1500 sheared trees was used (height, 1.2 to 1.5 m). Most trees had been in the field for 5 to 6 years and were likely 5 years from seed when planted. Trees shorter than 1.2 m or taller than 1.5 m as well as trees with noticeable disease or insect damage were not used. The completely randomized block design consisted of three sites with 50 blocks per site and 10 trees per block. Each tree was randomly assigned one of the 10 treatment combinations. Before the experiment, total tree height (growth through 2005) and the sheared height up to the previous year's whorl (growth through 2004) were recorded. Leader length for the 2005 growing season was calculated by difference. The length and the width of each tree's apical bud were measured using digital calipers. The two bud widths were averaged and multiplied by the apical bud length to derive a bud volume index. These measurements were taken to determine if there were significant relationships between the pretreatment measurements and final leader length