|dc.description.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.||