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Mackay River herbicide trial: conifer response 9 years post-treatment

Author(s) or contact(s): G.J. Harper, B.S. Biring, and J.L. Heineman
Source: Research Branch
Subject: Vegetation Management
Series: Research Report
Other details:  Published 1997. Hardcopy is available.


In 1986, glyphosate, 2,4-d amine, 2,4-d ester, and manual brushing treatments were applied to a 4-year-old fireweed/shrub community in the ESSFwk1 biogeoclimatic subzone, for the purpose of releasing Picea glauca engelmannii (hybrid spruce) seedlings. Competing vegetation was heavily affected for at least 1 year following application of glyphosate at a rate of 2.1 kg ai/ha. Spruce seedlings were also damaged by the herbicide, resulting in a net reduction in growth rates for 1986-1987. Manual brushing and 2,4-d amine treatments reduced vegetation cover less than glyphosate, while 2,4-d ester had little effect.

The trial was remeasured in 1995, 9 years post-treatment, to determine whether there were any long-lasting effects of treatment on growth and condition of planted spruce seedlings. Spruce seedlings in plots treated with glyphosate were significantly larger overall than seedlings located in the other treatments. Statistical analysis showed significant differences in spruce seedling root collar diameter, crown diameter, and height. Analysis of spruce height growth increments suggested that from 1989 to 1995 the glyphosate-treated seedlings were out performing seedlings from all other treatments.

Of the original target species (fireweed, black twinberry, Sitka alder, elderberry) of 1986, only fireweed continued to have significant cover within all treatments in 1995. Prominent vegetation species in 1995 were fireweed, thimbleberry, lady fern, and oak fern.

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Updated October 24, 2008