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Developing Strategies for Leader Length Control

A promising new leader control option involves the use of Plant Growth Regulators (PGR’s). This is a common practice in Europe with Nordmann and Turkish fir. Essentially the growth regulator slows or stops the extension of the leader and, in turn, increases the density of buds along the shortened leader. In this project, ProTone, an abscisic acid product was tested on four species. The product does not currently have a label for Christmas tree use. This trial showed promise. Applied at the correct rate and appropriate leader extension, leader length could be controlled within a few inches. In these trails, leader length control, with minimal damage, was effective on noble and Turkish firs at selective dosages. PGR applications on Fraser and Korean fir were less effective and will require further testing. Yet, even if the product is registered for use, cultural leader control techniques likely will remain the prevailing leader control method for the foreseeable future. Nordmann/Turkish fir (the two species are lumped together as many growers have both and they are hard to distinguish) respond differently to leader trimming than noble. Typically, noble leaders are often cut at the same time as the trees are sheared (August). This same strategy is often employed with Nordmann/Turkish with disappointing results. Alternative timing for trimming Nordmann/Turkish fir tested in this trial were, at budbreak and 30 days following budbreak. Results indicate that leader trimming at budbreak shows more consistent results than waiting 30 or so days to start trimming. By trimming Nordmann/Turkish fir leaders at budbreak growers should produce a higher % of straight tops, often multiple tops, than at other trimming times. Unlike noble fir, selecting specific buds or isolating individual buds is not effective with Nordmann/Turkish fir.