Field Note: Alternative Leader Growth Control for Fraser Fir and Korean Fir Christmas Trees

Excessive leader growth is a challenge for Christmas tree growers who are seeking about 30–35 cm (12–14 in.) shoot elongation for good balance between height and lateral growth. Current cultivation practices include manually pruning leaders to 30–35 cm. In this studywe investigated the use of a growth regulator Ethyl-naphthaleneacetate acid (NAA) and a girdling process using a five-bladed plier (Top-Stop Nipper, Monterey Lawn and Gardens Products, Inc., Fresno, CA) as alternative methods to slow leader growth in Fraser fir (Abies fraseri [Pursh]Poir.), and Korean fir (Abies koreana Wils). NAA applications at rates of 40–160 ml/L reduced the height growth in both Fraser fir and Korean fir. However, in Fraser fir, other morphological parameters such as the leader straightness and bud density were generally adversely affected.The highest rates of 250 and 500 ml/l caused unacceptable reduction in growth and in many cases leader death. NAA applications on Korean fir resulted in significant reduction of leader growth and significantly increased the bud density without negative impact on leader straightness. Partialgirdling of stems was not effective at reducing the leader height in both Fraser fir and Korean fir.