Abstract: CONFER is a potent plant growth regulator containing the active ingredient paclobutrazol. When applied to containerized conifer seedlings, CONFER provided short term control of height without affecting stem caliper growth. Treated seedlings exhibited a better balance between height and stem diameter than untreated seedlings. Seedlings treated with paclobutrazol became dormant and hardy faster than untreated seedlings and did not require blackout or other cultural treatments to induce dormancy. At effective rates of application, paclobutrazol resulted in a shift to root growth from shoot growth especially after outplanting. Seedlings treated with CONFER had higher levels of starch than untreated seedlings.

Introduction

CONFER is a plant growth regulator for use on conifer seedlings. It contains paclobutrazol, a potent plant growth regulator. CONFER was recently registered for use under the pest control products act (Reg. # 24199). Registered uses include use on white and black spruce and jack and lodgepole pine for control of shoot growth and induction of dormancy.

CONFER has been the subject of numerous laboratory, greenhouse and field experiments since 1987. From 1987 to 1990 physiological studies were the major focus of the research conducted. During this period CONFER was shown to dramatically improve the tolerance of conifer seedlings to stress caused by a variety of factors including drought, heat and high UV light. Researchers working in this area include Dr. Robert VanDenDriesshe, Dr. Dutch Dumbroff, John Marshall, Dr. Fred Beall, Dr. Gary Hogan and Dr. Helmut Krause.

From 1991 to present morphological studies have been the major focus of research with CONFER. In excess of 75 studies have been conducted by government, industry and University researchers across Canada on a range of conifer species.

Technical Profile

CONFER contains the active ingredient paclobutrazol which belongs to a group of chemicals called triazoles. Triazoles are a group of chemicals which include fungicides and plant growth regulators. CONFER is formulated as a suspension concentrate (SC) containing 250 g/l of the active ingredient paclobutrazol.

CONFER is of low toxicity to mammals both dermally and orally and does not accumulate in tissues. It is also of low environmental toxicity (birds, bees, earthworms, fish, micro-organisms...).

Uptake of CONFER is passive primarily by roots with some passive uptake through green plant parts. There is uptake by foliage however there is no movement from leaves to other plant parts. The active ingredient is xylem mobile from roots to actively growing plant parts. It is important to maintain treated plants under optimum growing conditions for 2-3 weeks to allow maximum uptake and translocation.

CONFER inhibits gibberelin biosynthesis in actively growing tissue by blocking the oxidation of kaurene to kaurenoic acid, a precursor of gibberelic acid.. Gibberelin is responsible for cell elongation an thus one result of treatment is reduced shoot growth. The growth inhibiting effects of CONFER can be reversed by the application of gibberelic acid.

The cytochrome P450 enzyme that CONFER affects is part of the Isopreniod pathway which is also responsible for the production of other related plant hormones. Other effects from treatment with CONFER include the stimulation of IAA production, increased levels of chlorophyll, starch, a cell wall protein and increased cuticular wax. The mode of action in these areas is not fully understood.

Documented effects of CONFER treatment include reduced height growth, improved height:diameter ratio, stimulated root growth (especially after outplanting), increase in starch reserves in shoots and roots, increased protein levels, increased free nitrogen, increased chlorophyll content, increased photosynthesis, reduced transpiration rate (especially when stressed) and reduced disease susceptibility.

Greenhouse Test Results

Greenhouse trials conducted in B.C. in 1994 and 1995 have demonstrated control of height growth with CONFER at rates of 1.0 to 5.0 kg a.i./1000 m2 (Figures 1&2). While height growth control has been obtained, stem caliper growth has continued resulting in improved height to stem diameter ratios (Figure 3). The result is a better balanced seedling compared to conventional growing techniques.

Figure 1: Effect of CONFER treatment on white spruce growth in 1994.	Figure 2: Effect of CONFER treatment on white spruce growth in 1995.
Figure 3: Effect of CONFER treatment on height : stem diameter ratio in white spruce.	Figure 4: Effect of CONFER treatment on Shoot:Root dry weights of white spruce seedlings.
While shoot growth is controlled root growth continues resulting in improved shoot:root dry weights (Figure 4). Root growth potential tests have demonstrated that seedlings treated with CONFER have greater root growth potential than untreated or conventionally produced seedlings (Figure 5).
Figure 5: Effect of CONFER treatment on root growth potential of white spruce seedlings.	Figure 6: Effect of CONFER on lodgepole pine height and stem diameter growth
CONFER is also effective in controlling height growth of lodgepole pine seedlings while allowing continued stem caliper growth (Figure 6). As was the case with white spruce, root egress is improved in CONFER treated lodgepole pine seedlings with significant increases in the number of white roots produced compared to untreated seedlings (Figure 7).
Figure 7: Effect of CONFER on lodgepole pine root egress at 8 weeks after treatment.	Figure 8: Effect of CONFER on water use of jack pine seedlings.
Transpiration rates of treated seedlings are reduced within several weeks of treatment. Tests with jack pine seedlings have demonstrated this effect (Figure 8). Treated seedlings should be watered as needed only with care taken to avoid overwatering. Independent laboratory analysis has also demonstrated that black spruce seedlings treated with CONFER have increased levels of starch in both roots and shoots (Figure 9).
Figure 9: Effect of CONFER on starch content in roots and shoots of black spruce seedlings.	Figure 10: Effect of CONFER on height and stem diameter growth of coastal fir seedlings.
CONFER has been evaluated on several species of conifers which are currently not on the registered label. Results on these species including coastal fir and western red cedar are similar to those observed on spruce and pine (Figures 10&11). Height to stem diameter ratios of coastal fir were improved at rates of 2.5 to 5.0 kg a.i./1000 m2 compared to the operational control treatment and bud set was improved at all rates evaluated except 0.25 kg a.i./1000 m2.
Figure 11: Effect of CONFER on bud set of coastal fir.	Figure 12: Effect of CONFER on western red cedar height and stem diameter growth.
CONFER provided control of height growth in western red cedar at all rates tested while allowing stem diameter growth (Figure 12). Height : diameter ratios were improved with the best response observed at 1.0 kg a.i./1000 m2. Outplanting Results Height and diameter growth of outplanted lodgepole pine at 66 weeks after treatment was not affected by CONFER applied at 1.0 to 2.5 kg a.i./1000 m2 (Figure 13). Both height and diameter growth of seedlings treated with CONFER at 5.0 kg a.i./1000 m2 was slightly reduced at 66 weeks after treatment. Height growth of white spruce treated with CONFER was slightly increased at 0.5 kg a.i./1000 m2 and reduced at higher rates while stem diameter growth was increased at 68 weeks after application (Figure 14). A negative dose response was observed with both height and stem caliper growth.
Figure 13: Outplanting performance of Lodgepole Pine.	Figure 14: Outplanting performance of white spruce treated with CONFER.
Shoot weight of white spruce after one year in an outplanting was increased at 0.5 to 1.0 kg a.i./1000 m2 while and decreased at higher rates while root weight was increased at all rates of CONFER tested. (Figure 15). The end result of CONFER treatment applied at 1.0 to 2.5 kg a.i./1000 m2 to white spruce was improved root growth parameters which should result in better establishment and improved long term performance.
Figure 15: Root dry weight of White Spruce seedlings treated with CONFER.

Conclusions

CONFER provided commercially acceptable control of height growth in both pine and spruce without the use of blackout or any other stress treatment. The effect of this treatment persisted for the remainder of the growing season. While shoot growth was controlled both stem caliper and root growth continued resulting in improved height to stem diameter ratios and improved shoot to root biomass ratios. A similar result was obtained with other species tested.

An improvement in seedling balance was the result of treatment with CONFER at rates of 1.0 to 5.0 kg a.i./1000 m2. Root growth potential tests demonstrated that CONFER treated seedlings had significantly better root growth potentials resulting in increased root biomass after outplanting. Optimum rates for improved root egress are at the lower end of the registered rate range of 1.0 to 5.0 kg a.i./1000 m2 while optimum height growth control was observed at the higher end of this rate range

Outplanting studies measured after one growing season demonstrated no effect on height and stem diameter growth of pine at rates of 1.0 to 2.5 kg a.i./1000 m2 while a slight reduction in both height and diameter were measured at the highest rate tested (5.0 kg a.i./1000 m2). Growth parameters of white spruce seedlings after one growing season were improved at rates of 1.0 to 2.5 kg a.i./1000 m2. CONFER provides a useful tool to the conifer seedling grower for controlling height growth and inducing dormancy while allowing shoot diameter and root growth. Seedlings should establish better at the planting site and reach free to grow status earlier than seedlings produced by conventional means.

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