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Home → Publications → Tree Planters' Notes → Tree Planters' Notes Volume 58, Number 2 (2015) → Using Plant Growth Regulators on Red Alder and Douglas-Fir Plugs

Using Plant Growth Regulators on Red Alder and Douglas-Fir Plugs

Treatments of 50 ppm, 50 ppm (two applications), 100 ppm, and 200 ppm and also 5 and 10 ppm drench applications of the plant growth regulator (PGR) Bonzi® (paclobutrazol) significantly reduced height growth while maintaining stem diameter growth in red alder (Alnus rubra Bong.) container seedlings, resulting in a sturdy, compact seedling at transplant. Although the use of PGR facilitated the midseason transplanting process, end-of-season height, stem diameter, and packout totals of field-transplanted seedlings were not significantly different than the control group. In a second trial, Bonzi and Sumagic® (uniconazole-P) PGRs were applied to coastal Douglas-fir (Pseudotsuga menziesii [Mirb.] Franco) container seedlings to help stimulate shutdown. Treatments of 10, 20, and 40 ppm Sumagic® significantly reduced height growth compared with control seedlings, but stem diameter growth was significantly reduced as well. Bonzi® treatments of 50, 100, and 200 ppm did not significantly reduce height growth, while stem diameter growth was slightly lower than controls. Only the 10 ppm Sumagic® treatment produced sturdier (lower height-to-stem diameter ratio) seedlings compared with control seedlings. Used in conjunction with other cultural techniques, PGRs may offer the grower another tool to manipulate seedling growth. At this time, PGRs show more promise in red alder than Douglas-fir seedling production. This paper was presented at a joint meeting of the Western Forest and Conservation Nursery Association, the Intermountain Container Seedling Growers Association, and the Intertribal Nursery Council (Boise, ID, September 9–11, 2014).


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Author(s): Nabil Khadduri

Publication: Tree Planters' Notes - Volume 58, Number 2 (2015)

Event: Joint Meeting of the Western Forest and Conservation Nursery Association, the Intermountain Container Seedling Growers Association, and the Intertribal Nursery Council
2014 - Boise, Idaho

Volume: 58

Number: 2