Glyphosate herbicide for the control of aspen in a white spruce plantation in Manitoba

Abstract

Three experimental herbicide trials were established within a white spruce plantation located in the Porcupine Provincial Forest of the Mixedwood Section (B.18a) (Rowe 1972) of western Manitoba. The trials were as follows: 1) the aerial application of glyphosate at three rates, 2) the ground application of glyphosate at three rates at three periods of time during the growing season, and 3) the evaluation of the resuckering potential of aspen from the ground spray trial. The results of these trials indicates that the optimum time to apply glyphosate for white spruce release in Manitoba occurs in mid-late August after the buds have set and during the time when there is relatively little shoot growth. Glyphosate applied at 1.0 kg.ha-1 provided the best silvicultural and herbicidal efficacy. In areas where complete control of aspen is not desirable, lower rates of application should be considered. Such areas may include frost pockets or areas of high aesthetic value. The percent kill and the resuckering potential of aspen was influenced by both the rate and the time of glyphosate application. Rate was more critical than the time of application for both percent kill and regrowth potential. Regrowth potential of aspen on areas treated with 0.5 kg.ha-1 was relatively high compared to aspen from areas treated with 1.0 kg.ha-1. The full effect of glyphosate on trembling aspen competition did not become apparent until the second year after application. White spruce showed a positive growth response within two growing seasons after the application of glyphosate in both the aerial and the ground spray trials. Although small gains in height increment were realized, the greatest gains were from diameter and volume increment.