Alterations of growth and shikimic acid levels by sublethal glyphosate applications on pin cherry and trembling aspen

Field experiments were conducted to evaluate the effect of low doses of glyphosate (0.04–0.5 kg/ha) on pin cherry (Prunuspensylvanica L.f.) and trembling aspen (Populustremuloides Michx.) trees in conifer plantations. Applications were repeated twice over a 2-year period, with treatments applied in late July and growth assessments made 1 and 2 years later. Growth and vigour of these species, measured as percent mortality, visual injury, and leaf and stem lengths, continued to be affected 2 years after treatment even with the lowest rate of glyphosate. Shikimic acid levels were substantially increased within 2 days after herbicide application and could be used to assess glyphosate damage in the field before visual symptoms become apparent.