EFFECT OF PACLOBUTRAZOL ON FLOWER-BUD PRODUCTION AND VEGETATIVE GROWTH IN 2 SPECIES OF EUCALYPTUS

A series of experiments on field-grown seed-derived trees between 2 an d 17 years old demonstrated that the growth regulator paclobutrazol co uld be used to reduce vegetative growth and enhance flower-bud product ion in Eucalyptus globulus Labill. and Eucalyptus nitens (Dean & Maid. ) ex Maid. Responses to high levels of trunk injection and collar dren ching persisted for up to six growing seasons, yielding both increases in frequency of flowering and heaviness of bud crop. Growth responses were expressed in the immediate growing season, but flowering respons es were not evident for another year. Foliar spray treatments reduced vegetative growth in young trees of both species for one growing seaso n, but only the E. globulus showed an associated flowering response. A ssessment of seed yield per capsule and subsequent germination tests s howed no deleterious effects on seed development or quality. Choice of application method will vary with objective and size of tree. Collar drenching shows the most promise for treating large numbers of seed or chard trees because application time is substantially independent of t ree size and weather conditions.