Glyphosate-resistant (GR) cropping systems are popular and used extensivelyby producers. However, the long-term impacts of heavy reliance of thistechnology on weed community structure are not known. Five fully phasedfield experiments (two no-tillage and three conventional tillage) wereestablished at four locations in southwestern Ontario where the effects ofherbicide system (glyphosate or conventional) in corn and soybean and croprotation (corn–soybean or corn–soybean–winter wheat) on midseason weedcommunities were examined. Multivariate analysis on data over the last 3 yrof the 6-yr experiment showed that weed communities were distinctlydifferent among the treatments within each experiment. At several locations,midseason weed communities were more similar in corn and soybean treatedwith glyphosate compared to the same crops treated with conventionalherbicides, reflecting the continuous application of the same selectionpressure in both crops. Analysis of trait-densities revealed an increase inspecies with late initiation of seedling recruitment at the expense of weedspecies with medium time of initiation of seedling recruitment rather thanearly recruiting species. Increases in perennial species, species with ashort interval between recruitment and anthesis, and wind-dispersed specieswere also observed. Trait-density–based analysis of the weed community wasan effective method for reducing the complexity of divergent weedcommunities that enabled direct quantitative comparison of theherbicide-induced effects on these weed communities.