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 of the transformations that occurred during the 1970s-2000s in western Canada. How these transformations in canola-based crop rotations impacted weed communities are not comprehensively studied. 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 frequency of canola in the rotation can impact weed abundance, composition, and diversity in the Canadian prairies. Weed survey data revealed that the frequency of many weed species declined in years after 1995 compared with before 1995, the year HR cultivars were introduced. Gallium spurium (false cleavers) 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. Glyphosate-resistant (G.R.) systems were associated with green foxtail irrespective of their frequency in the rotation. Wild oat was predominant in the longer rotations with glufosinate and imidazolinone-resistant canola. In the field study, weeds associated with pre-herbicide weed control timing were relatively controlled when herbicides were applied (glyphosate and glufosinate), except for foxtail barley (Hordium 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 growing of HR canola cultivars.