Weed surveys of annual crops have been regularly conducted in the Prairie Provinces since the 1970’s.  In the 1990’s, a herbicide resistance component was added to the provincial surveys.  The objectives of the project were to complete the sixth set of weed surveys in the Prairie Provinces and summarize previous weed survey information to help identify changes in weed populations. 

From 2019 to 2023, weeds were surveyed in 4098 fields of annual crops in the Prairie Provinces. Saskatchewan was surveyed in 2019 and 2021, Manitoba in 2022 and Alberta in 2023. Crops surveyed included: spring wheat, barley, durum, oat, canola, flax, mustard, soybean, lentil, pea, chickpea, corn, pinto bean and sunflower. Weed data are summarized using a relative abundance index based on frequency, field uniformity and density. Similar methodology has been used since the beginning of the survey program, enabling the identification of shifts in weed communities.  

The fields were distributed amongst Eco districts (areas with similar in landform, relief, surficial material, soil, vegetation and land use based on the seeded area of the selected crops.  Sites were randomly selected from all quarter sections (65 ha) that have greater than 16 cultivated hectares.  Owners were then identified and contacted to seek permission to survey their land.  Weeds that had not been controlled in the fields were counted in mid-July through to September.  At this time, the weeds in the field are, in part, a result of the agronomic management decisions made by the farm operator at various times during the crop year.  Counts at this time of the year show the size and extent of troublesome weed populations.  Within each field, weeds are counted in 0.25-metre square quadrats (50 cm by 50 cm) at 20 locations in a set pattern, avoiding any edge effects.  The weed data was also summarized in a similar fashion to previous surveys to allow direct comparisons.  Weeds were ranked using a relative abundance index based on frequency (percent of surveyed fields with the weed), field uniformity (percent of quadrats with the weed within a field) and density.   

While the number one ranked weed, green foxtail, has not changed since the onset of the survey program, several weeds were identified as increasing. In particular, there was an increase in the relative abundance of volunteer canola in all three provinces, ranking second overall in the current round of surveys. Other volunteer crops that have increased in abundance over time include: wheat, barley, and lentil. The increased presence of volunteer crops as weeds reflects both the increased acreage of these crops and diversification of crop rotations. Kochia also ranked higher than any previous survey in all provinces, likely due both to favourable weather and the spread of herbicide-resistant biotypes. Other weeds increasing include spiny annual sow-thistle, false cleavers, foxtail barley, broad-leaved plantain, barnyard grass species and dandelion.  Some emerging regional species identified in this survey include golden dock, green pigweed and yellow foxtail in Manitoba, black medick in Saskatchewan and annual blue grass in Alberta. Other weeds of concern include round-leaved mallow, biennial wormwood, annual brome species and stink grass. 

Weeds identified as increasing in abundance can be targeted for attention by various agencies involved in weed science. The trends identified by the weed surveys are important to the research, industry, and extension communities for developing weed management recommendations for producers that are essential components of sustainable farming systems.  

Regular weed surveys are necessary to detect changes in weed populations. Further monitoring is necessary to determine if the high relative abundance of some species was related to weather in the survey year, or if these species are increasing in abundance due to other factors. Future surveys could also determine the impact of emerging herbicide resistant weeds, and any mitigation practices that are adopted.  

The Prairie Weed Monitoring Network website is currently being developed to increase accessibility to weed survey data.  The website will include data from each of the Prairie Weed Surveys starting in the 1970’s.