A research trial was established in 1986 to study the effect of glyphosate applied at 3 L/ha (1.07 kg ai/ha), glyphosate applied at 6 L/ha (2.14 kg ai/ha), and manual cutting on release of 4-year-old planted Engelmann spruce seedlings and concurrent suppression of the Willow Complex in the southern interior of British Columbia. Engelmann spruce seedlings and two target species (willow and fireweed) were assessed for 3 years following treatment, and then again in the ninth year.
Treatment efficacy was poor in this trial. Manual cutting significantly reduced willow height for 1 year, but had no effect on cover, and neither glyphosate treatment had any effect on height or cover of willow. Whereas the quick recovery of willow following manual cutting is typical of other research trials, the lack of glyphosate injury contrasts with other studies that show that willow can be severely damaged. Fireweed height was significantly reduced by both levels of glyphosate for 3 years following treatment, but actually changed little in comparison to the control. Glyphosate efficacy may have been reduced by rainfall soon after application, and by the presence of the willow leaf rust, Melampsora epitea Thuem., which may have reduced uptake of the herbicide.
None of the three treatments has significant effects on height or stem diameter of Engelmann spruce seedlings. Survival of Engelmann spruce seedlings was good throughout the trial, and at about 10-11 years of age they naturally outgrew the willow canopy.
FRDA Research Report 258 (1993 KB)
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Updated July 24, 2015