Ten-year growth and survival of Douglas-fir seedlings treated with plant growth regulating substances at transplant

Commercially available plant growth regulators (PGRs) or moisture retention gels, applied to the roots of Douglas-fir (Pseudotsuga menziesii (Mirb.) F ranco) before planting, can modify indole-3-acetic acid (IAA) levels in roo ts, root growth responses, and tree survival. We treated two different 1+0 stock types (PSB313B and PSB323) of Douglas-fir with indole-butyric acid (I BA), ethephon (Ethrel(R)), alginate, or a combination of IBA and alginate. New root growth and IAA levels in roots were measured 2 weeks after plantin g, and aboveground growth and tree survival were monitored over 10 growing seasons after planting. Treatment with IBA or the combination of IBA and al ginate increased IAA conjugate and free IAA levels in roots, root growth, a nd tree survival. Alginate treatment alone increased new root growth and tr ee survival, but did not increase free IAA levels in roots. Ethrel(R) treat ment increased free IAA levels and root growth, but had no effect on IAA co njugates or tree survival. A cost analysis suggests that use of certain PGR s or alginate decreases the cost required to attain target stocking and inc reased tree size. Our results suggest that application of PGRs or other roo t-promoting materials to the roots of Douglas-fir before planting has the p otential to be a cost-beneficial method for increasing root growth and tree survival.