Distribution of Glyphosate and Cloransulam-Methyl Resistant Giant Ragweed (Ambrosia trifida L.) Populations in Southern Ontario

Giant ragweed is a species of flowering plant in the sunflower family. It is native to North America, and can also be found in orchards and non-cropped areas such as ditches and river banks in southern areas of Canada and the Midwestern and Eastern United States. It is an erect annual broadleaf weed and has a long emergence period lasting from early March to late July. It also has the ability to grow rapidly and can reach heights of up to 6 m.

Actually, giant ragweed is also a very competitive weed in row crop production and has been found to drastically reduce soybean yield. In 2008, giant ragweed was the first weed species with confirmed resistance to glyphosate in Canada. As of 2010 there were 48 locations with confirmed glyphosate resistant giant ragweed in Essex, Kent and Lambton counties. In addition, there was suspected resistance to cloransulam-methyl.

The objectives of this research were 1) to conduct an expanded field survey on the distribution of glyphosate resistant giant ragweed in Ontario, 2) to determine the distribution of cloransulam-methyl resistant giant ragweed in Ontario, and 3) to determine the distribution of multiple resistant (glyphosate and cloransulam-methyl) giant ragweed in Ontario.

In 2011 and 2012 giant ragweed seed was collected from 85 field sites in Essex (16), Kent (34), Lambton (23), Elgin (3), Middlesex (6), Lennox & Addington (1), Huron (1) and Brant (1) counties. In total, there were 34 additional locations confirmed with glyphosate resistant giant ragweed in Ontario. There were 11 locations confirmed with cloransulam-methyl resistant giant ragweed and 5 locations with multiple resistance to both glyphosate and cloransulam-methyl.

In summary, this survey demonstrated that glyphosate resistant giant ragweed was no longer confined to the southwestern portion of Ontario. Since the initial assessment of its distribution in Ontario, the presence of glyphosate-resistant giant ragweed had been confirmed in four additional counties.

Article by Yuji Mitadera, et al, from Japan.

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Image by Tim Martin, from Flickr-cc.