The Real Christmas Tree Board

Early cone production is a major concern for Christmas tree growers that produce Fraser fir. Trees often produce heavy amounts of cones that must be removed by hand, resulting in significant labor costs. In this project, we hypothesized that plant growth regulators that inhibit GA synthesis or translocation would reduce cone formation in Fraser fir. In a series of trials at four farms in Michigan, we applied paclobutrazol as a one-time soil injection (Tradename: Cambistat®) and as an annual foliar spray (Tradename: Trimtect®). We evaluated coning for 3 years (4 years on 2 sites) and found that the high rate of soil injected paclobutrazol reduced coning across all site by approximately one-third, and reduced coning by up 67%. Paclobutrazol also reduced leader growth by up to 8 cm. Effects of soil application of paclobutrazol persisted three to four years. In a second series of trials we evaluated four different GA-inhibitors (Citadel®, Concise®, Dazide®, and Trimtect®), which were applied annually as foliar sprays. Responses varied among sites, but paclobutrazol reduced coning by up to 70% on one site. The results indicate that GA inhibitors can disrupt cone formation in Fraser fir. Depending on the level of coning on a given farm, the cost of application could compare favorably with manual cone removal. Work is on-going and additional trials will compare the potential of additive effect of combining soil and foliar applications.