New network provides Prairie weed strategy

The new Prairie Weed Monitoring Network (PWMN) provides information required to manage weeds effectively, anticipate new weed threats and mitigate selection pressure for herbicide resistant weeds. The Prairie-wide effort, following the model of the Prairie Pest Monitoring Network and Prairie Crop Disease Monitoring Network, is a collaboration of research and extension efforts across Manitoba, Saskatchewan and Alberta. It is a Sustainable Canadian Agricultural Partnership project with many commodity funders.

The network website, at PrairieWeeds.com, states that Canada has the third largest number of unique herbicide-resistant weed biotypes, with about two new herbicide-resistant weed biotypes discovered each year since the 1990s. The 2014-2017 data suggests 59 per cent of Canadian Prairie fields contain at least one herbicide-resistant weed biotype, and that herbicide resistance costs farmers on the Prairies an estimated $530 million annually in reduced crop yield and crop quality, and in increased weed control.

The PWMN explains that herbicide resistance is the inherited ability of a plant to survive and reproduce following exposure to a dose of herbicide normally lethal to the wild type. Herbicide tolerance is the inherent ability of a species to naturally survive and reproduce after herbicide treatment (with no selection or genetic manipulation to make the plant tolerant).

Past provincial weed survey results

The PWMN website features Weed Abundance and Herbicide Resistance survey results. Here are a few highlights from the reports:

• The 2014-15 Saskatchewan results concluded that: Relative abundance of annual grass has decreased since the 1970s, while relative abundance of perennials and facultative winter annuals has increased since 2003. Weed densities were higher in 2014-15 than in 2003, likely due to the wet conditions in 2014.
• The 2016 Manitoba results, when compared to surveys in 2002, 1997, 1986 and 1978-1981, had the lowest relative abundance of annual grasses but the highest relative abundances of perennials and facultative winter annuals (which can emerge in both spring and fall). For the 2016 survey, densities of annual grass and annual broadleaved weeds were the lowest ever recorded.
• The 2017 Alberta results reported that total weed densities in 2010 and 2017 were the lowest recorded. Foxtail barley abundance was also found to have increased the most since the 1970s and 2017 marked the first time that it was among the top 25 weeds.

Researchers noted that pre-emergence herbicides can reduce weed population recruitment and abundance in-crop, thereby potentially reducing in-crop herbicide selection pressure for resistance.

Integrated weed management

The ongoing weed abundance and herbicide-resistance challenges highlight the need for additional management strategies to control weeds, in addition to chemical options.

Integrated weed management (IWM) includes a combination of cultural, physical, or biological control strategies in addition to herbicide-based management options.

The recent ‘Effective integrated weed management starts early and varies by species’ blog on the Canola Research Hub examines outcomes of recent IWM studies, including:

• A five-year ‘Mitigating herbicide resistance – investigating novel integrated weed management systems’ project and its related ‘Using integrated weed management systems to manage herbicide-resistant weeds in the Canadian Prairies’ publication.
• The ‘Harrington seed destructor evaluation at field scale in Alberta’ project and related ‘Field testing of a physical impact mill in the Canadian Prairies’ publication.

For more options, check out the Canola Watch Fundamentals article called “Integrated weed management: Best practices,” which includes reference to the ‘Top 10 Herbicide Resistant weed Management Practices’ by research scientists Neil Harker and Hugh Beckie.

Read the full summary and report on the Canola Research Hub
at CanolaResearch.ca.