Seed cone production enhanced by injecting 38-year-old Larix occidentalis Nutt. with GA(4/7)

The influence of injecting 38-year-old Larix occidentalis with gibberellin A(4/7) (GA(4/7)) on seed and pollen cone production was studied in western Montana, U.S.A. Two natural stands thinned to several spacings in 1961 were chosen. The two widest spacings were used. In 1991, 60 trees selected for study at each site were randomly divided into two groups of similar DBH, ha lf as controls and half injected in June 1991 with a solution of GA(4/7) in ethyl alcohol. The volume injected was adjusted to the DBH of each tree (6 0 mg per 5 cm diameter). In June 1994, half the trees treated with GA(4/7) in 1991 and half the untreated trees were injected with GA(4/7) in the same manner as before. In 1992 and 1995, seed cone production increased on GA(4 /7)-treated trees compared to the controls. Pollen cone production was sign ificantly increased by GA(4/7) treatment but only at one site. Delayed effe cts of GA(4/7) on seed cone production was not evident in subsequent years after treatment. Foliar and shoot damage on treated trees was attributed to GA(4/7) treatment but most trees recovered completely the following year. Finally, GA(4/7) treatment did not affect cone length, potential seed per c one or filled seed per cone.