RESPONSE OF WOODY EASTERN CANADIAN FOREST WEEDS TO FALL FOLIAR TREATMENTS OF GLYPHOSATE AND TRICLOPYR HERBICIDES

Second-season post-treatment efficacy data are presented for a New Bru nswick field study comparing three formulations of glyphosate (VISION( R), MON14420, and TOUCHDOWN(R)) and a single formulation of triclopyr (RELEASE(R)). Five rates of each herbicide were broadcast applied to a 2-year-old clearcut in early September. Two growing seasons after tre atment, percent control values (based on total woody crown area) range d from 21% at glyphosate rates <0.25 x label maximum to more than 80% at rates greater than or equal to 0.75 x label maximum. Coefficients o f variation for percent control values decreased from 104% at the lowe r glyphosate rates to 9% at the higher rates. Total woody control prov ided by triclopyr was generally equivalent to that of glyphosate at ra tes <0.5 x label maximum. Beyond this rate, percent control values for triclopyr averaged only 59% and coefficients of variation remained hi gh (40%). At the individual-species level, the three glyphosate formul ations provided greater crown volume reduction than triclopyr for whit e ash (Fraxinus americana L.), beech (Fagus grandifolia Ehrh.), hazel (Corylus cornuta Marsh.), and sugar maple (Acer saccharum Marsh.). Con trol of mountain maple (Acer spicatum Lam.) by TOUCHDOWN(R) was found to be slightly inferior to that of the other two glyphosate formulatio ns. Control of elderberry (Sambucus pubens Michx.) by MON14420 was inf erior to that of the other three herbicides. Nonlinear regression curv es relating second-season control and herbicide dose are presented as a guide for silvicultural use.