The impact of herbicide-resistant canola systems on the weed community dynamics in the Canadian Prairies

Abstract

Increased adoption of no-till and extensive cultivation of herbicide-resistant (HR) crops in low diversity rotations are some transformations that occurred during the 1970s–2000s in western Canada. Historical data analysis of weed survey data (Saskatchewan, Manitoba, and Alberta) in canola crops and a canola rotation field experiment were used to understand how tillage, herbicide-resistant cropping systems, and the temporal frequency of canola in the rotation can impact weed abundance, composition, and diversity in the Canadian prairies. Weed survey data revealed that the spatial frequency of many weed species declined in years after 1995 compared with before 1995, the year HR cultivars were introduced. False cleavers ( Galeum spurium L .) and volunteer wheat ( Triticum aestivum L.) were the only species showing a continuous increase in frequency throughout the surveyed years. Species richness showed no trajectories but varied depending on climatic conditions. Roundup-Ready (RR) systems were associated with green foxtail ( Setaria viridis L.) irrespective of their frequency in the rotation. Continuous canola systems had an obvious association with chickweed ( Stellaria media L.) regardless of herbicide systems. Wild oats ( Avena fatua L.) were predominant in the longer rotations with glufosinate and imidazolinone-resistant canola. In the field study, weeds associated before in crop herbicide application were relatively controlled after herbicides were applied, except for foxtail barley ( Hordeum Jubatum L.), which was not controlled in most HR systems. Overall, both weed survey data and field experiment data revealed greater control of most weed species due to the adoption of HR canola cultivars and the associated cultural practices.