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Pearce: Concerns over glyphosate resistance seen rising

A recent survey by Stratus Agri-Marketing of Guelph has found concerns on the rise about herbicide-resistant weeds among farmers in Eastern Canada — specifically, resistance to glyphosate is gaining more attention.

In the U.S., an online survey in 2012 found upward of 61.2 million acres of cropland have some species of glyphosate-resistant weed. That’s almost one in four acres in the U.S., and nearly double the 32.6 million acres with one resistant species in 2010.

More alarming, 49 per cent of farmers surveyed across 31 states say they now have glyphosate-resistant weeds on their farms. In Georgia, that number jumped to 92 per cent. In one year — from 2011 to 2012 — Nebraska, Iowa and Indiana saw a near doubling of acres with resistant weeds.

Canada fleabane, known as marestail and horseweed in the U.S., is the dominant resistant weed; second place goes to Palmer amaranth, which has yet to enter Canada (but has been confirmed in Michigan, Indiana and Ohio).

In Canada, the survey indicates 1.07 million acres of glyphosate-resistant weeds. As a percentage, that’s only 1.4 per cent of land farmed or 6.7 per cent of growers. Western Canada reported 788,000 acres of glyphosate-resistant weeds, while Eastern Canada reported 281,000 acres.

To date, there are five species confirmed to be resistant to glyphosate across Canada: kochia, Canada fleabane, giant ragweed, volunteer canola and common ragweed.

Resistant common ragweed was confirmed in one field in Ontario by researchers from the University of Guelph. Seeds from the plant were actually collected in 2011, and confirmed to be resistant to glyphosate during late summer of 2012. Growers in the survey, however, listed 10,000 affected acres in Ontario (about 8,900) and Atlantic Canada (about 1,000).

What’s also telling about this study is the rising number of growers concerned with resistance on a regional basis. In Ontario, despite having four resistant weed species (including volunteer canola), 40.5 per cent of growers surveyed expressed concern about this issue. By comparison, 49.3 per cent of Quebec growers indicated they were concerned with glyphosate resistance — yet the only resistant weed species in Quebec is giant ragweed, impacting 11,000 acres.

According to the survey, Ontario has 180,000 acres with glyphosate-resistant Canada fleabane, 78,000 acres with resistant giant ragweed and 13,000 acres where resistant volunteer canola is a problem. In all, 12.5 per cent of growers in Ontario are believed to be affected.

The methodology of the survey included 2,028 growers interviewed across Canada. The survey was conducted from Feb. 1 to March 13, with those interviewed accounting for 4.4 million acres of field crops.

Surveyed growers covered a very wide spectrum of crops on their operations, including corn, wheat and soybeans, but also on a cross-Canada basis, rye, canola, dry peas, lentils, mustard, dry beans and potatoes. Online interviews were conducted with farmers from three Prairie provinces, as well as the Peace region in B.C., and in Ontario, Quebec and the Atlantic provinces.

The study also contains a summary of the U.S. survey, and mentions Palmer amaranth is the second most frequent resistant weed species in the U.S.

Since 2010, Palmer amaranth has migrated north relatively quickly, from the northern tier of Arkansas and Mississippi, through Missouri, into Illinois and Indiana. Its spread has been a huge concern to researchers because it’s generally assumed that the weeds are resistant to glyphosate.

— Ralph Pearce is a field editor for Country Guide at St. Marys, Ont.

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