Glyphosate-resistant (GR) giant ragweed, horseweed, and common ragweed wereconfirmed in southwestern Ontario, Canada in 2008, 2010, and 2011,respectively. In the western prairie provinces of Alberta and Saskatchewan,GR (plus acetolactate synthase inhibitor-resistant) kochia was discovered in2011. This symposium paper estimates the environmental impact (EI) of thetop herbicide treatments or programs used to manage these GR weed species inthe major field crops grown in each region. For each herbicide treatment, EI(per ha basis) was calculated as the environmental impact quotient (EIQ),which quantifies the relative potential risk of pesticide active ingredientson human and ecological health based on risk components to farm workers,consumers, and the environment, multiplied by the application rate (kg ai ha−1). Total EI is defined as EI (per ha basis) multiplied bythe application area (i.e., land area affected by a GR weed). It was assumedthat all herbicide treatments would supplement the continued usage ofglyphosate because of its broad spectrum weed control. For the control ofthese GR weeds, most treatments contain auxinic or protoporphyrinogenoxidase (PPO)-inhibiting herbicides. The majority of auxinic herbicidetreatments result in low (EI ≤ 10) to moderate (11 to 20) EI, whereas alltreatments of PPO inhibitors have low EI. Total EI of GR horseweed andkochia will generally be greater than that of giant or common ragweedbecause of rapid seed dispersal. For recommended herbicide treatments tocontrol GR weeds (and herbicide-resistant weeds in general), EI data shouldbe routinely included with cost and site of action in weed control extensionpublications and software, so that growers have the information needed toassess the EI of their actions.