Comparison of weed communities in Manitoba ecoregions and crops

In 1997, a weed survey was conducted during July and August in fields of wh eat, barley, oat, canola and flax in Manitoba. Field selection was based on a stratified-random sampling methodology using ecodistricts as strata. Spe cies in the Poaceae family were most commonly observed in the survey, follo wed by species in the Polygonaceae, Asteraceae and Brassicaceae families. T he six most abundant weed species were green foxtail [Setaria viridis (L.) Beauv.], wild oats (Avena fatua L.), wild buckwheat (Polygonum convolvulus L.), Canada thistle (Cirsium arvense L.), red-root pigweed (Amaranthus retr oflexus L.) and wild mustard (Sinapis arvensis L.). The survey highlighted significant differences between ecoregions and between crops in residual we ed infestations. The weed community in the Boreal Transition ecoregion was dominated by seven species, whereas fields in the Aspen Parkland and Lake M anitoba Plain ecoregions were dominated by two species and the Interlake Pl ain ecoregion was dominated by only one species. Although significant diffe rences were found between the weed communities in crops, they were not as g reat as differences between ecoregions. The Manitoba residual weed communit y in 1997 was very similar to that reported for 1978-1981 and 1986, suggest ing that the same species should remain a focus for weed management.