EFFECT OF PACLOBUTRAZOL ON DOUGLAS-FIR AND LOBLOLLY-PINE

Paclobutrazol significantly reduced the growth of Douglas fir (Pseudotsuga menziesii) and loblolly pine (Pinus taeda) seedlings when applied as a soil drench to newly germinated, container-grown trees. Shoot growth, in general, was inhibited more than root growth. Older trees (three and nine years old) were not affected appreciably by soil drench or stem injection of the growth regulator. Dose response varied significantly among half-sib families for nearly all growth traits. The utility of paclobutrazol as a growth regulating agent in conifer seed orchards appears to be limited, although the chemical may find use in container-grown conifer nurseries.