Effect of growth regulators, girdling, and mulching on flowering of young European and Japanese larches under field conditions

Abstract

Two experiments were undertaken in 1977 and 1979 to promote flowering of 5- and 7-ycar-old field-grown seedlings of Larixleptolepis Gord. and L. decidua Mill. A gibbcrellin A4/7 mixture (GA4/7) was applied alone or in combination with GA3 and naphthalene acetic acid (NAA) to both girdled and nongirdled trees or branches by two methods, perfusion into the xylem and spraying with an aqueous cationic surfactant solution. Perfusion was most effective, especially on girdled branches, although spraying was reasonably effective for male flowering in L. decidua. Only GA4/7 alone significantly increased flowering. Male flowering was doubled and female flowering increased eightfold by GA4/7 in the best treatments, over all application dates. Generally, male flowering doubled and female flowering increased eightfold by GA4/7. Even more flowering was obtained at optimal application dates. May and June applications were best, especially for treatments associated with girdling. However, some flowering occurred with applications as late as August and September. More strobili of both sexes develop in the upper crown. However GA4/7 treatment induced seed cone buds to appear in the lower crown, an abnormal location. An unusual effect occurred in that a positive flowering response of the 1977 experiment occurred only in 1979, whereas the 1979 experiment yielded enhanced flowering in 1980. Soil mulching with a plastic film, with or without hormone treatment, was a very effective adjunct treatment for both male and female flowering.