Response of woody eastern Canadian forest weeds to fall foliar treatments of glyphosate and triclopyr herbicides

Abstract

Second-season post-treatment efficacy data are presented for a New Brunswick field study comparing three formulations of glyphosate (VISION®, MON14420, and TOUCHDOWN®) and a single formulation of triclopyr (RELEASE®). Five rates of each herbicide were broadcast applied to a 2-year-old clearcut in early September. Two growing seasons after treatment, percent control values (based on total woody crown area) ranged from 21% at glyphosate rates < 0.25 × label maximum to more than 80% at rates ≥ 0.75 × label maximum. Coefficients of variation for percent control values decreased from 104% at the lower glyphosate rates to 9% at the higher rates. Total woody control provided by triclopyr was generally equivalent to that of glyphosate at rates < 0.5 × label maximum. Beyond this rate, percent control values for triclopyr averaged only 59% and coefficients of variation remained high (40%). At the individual-species level, the three glyphosate formulations provided greater crown volume reduction than triclopyr for white ash (Fraxinusamericana L.), beech (Fagusgrandifolia Ehrh.), hazel (Coryluscornuta Marsh.), and sugar maple (Acersaccharum Marsh.). Control of mountain maple (Acerspicatum Lam.) by TOUCHDOWN® was found to be slightly inferior to that of the other two glyphosate formulations. Control of elderberry (Sambucuspubens Michx.) by MON14420 was inferior to that of the other three herbicides. Nonlinear regression curves relating second-season control and herbicide dose are presented as a guide for silvicultural use.