Promotion of cone production on white spruce grafts by Gibberellin A4/7 application

White spruce [Picea glauca (Moench) Voss] grafts growing in a seed orchard were sprayed with gibberellin A_4/7 (GA_4/7), either at different periods of time during the growing season or in different concentrations, for a 3-year period. Whole-tree spraying in May through July 1983 significantly increased cone production in 1984, while spraying in June through August of the same year was not effective. The best treatment in branch spraying was at the highest concentration (800 mg/L GA_4/7). The spray was effective in a good, but not a poor, crop year. Vegetative budburst occurred in the first half of May and shoot elongation ended in late June. Needle primordia in a newly formed bud were not discernible until the end of June. Application of GA_4/7 during the period of bud scale initiation and shoot elongation, and before needle primordial initiation, could have influenced the course of bud differentiation to increase the formation of reproductive buds.