Weed communities associated with arable Saskatchewan farm management systems

The objective of this study was to determine the impact of a range of manag ement systems on weed communities in cropped fields on farms in Saskatchewa n. Farms (n = 28) with management systems defined by a combination of diffe rent cropping histories and chemical input levels were selected. Fields wer e surveyed on each farm in 1995, 1996, and 1997 after any post-emergent wee d control to ensure that their weed communities reflected the impact of all agronomic management practices typical of the management system. Canonical correspondence analysis was used to determine whether weed communities wer e significantly correlated with management system after removal of variance due to ecoregion and year. The largest difference in weed communities attr ibutable to fanning system was between the systems with annual cropping his tories and those that included perennials in the cropping history. Thus, th e life history of the weeds reflected the life history of the crops. Herbic ide use was correlated with the next largest difference between systems. A significant association between weed communities and different management s ystems indicates that weed species are being selected for by these systems. If such selection pressure continues, these species may become a threat to the system's sustainability.