Posted: November 22, 2010

University of Guelph scientists confirmed that they have found additional glyphosate-resistant giant ragweed populations, following their work last spring which turned up the first such case. This information was shared in a recent news release from Monsanto, the manufacturers of Roundup.

Greenhouse testing of seed samples collected from the Essex, Kent and Lambton counties of southwestern Ontario, confirmed that 16 additional fields had populations of giant ragweed that were resistant to glyphosate. "As was the case in our initial finding on a field near Windsor in 2008, we have been able to demonstrate that plants from the populations of giant ragweed we collected in 16 of the 57 fields survived when they were sprayed with glyphosate in the greenhouse," said Dr. Francois Tardif, department of plant agriculture, University of Guelph.

Currently, 30 species of weeds in Canada have developed resistance to herbicides but only the giant ragweed has a confirmed glyphosate resistance. Worldwide, there are 20 species of weeds considered glyphosate-resistant, and 10 of those species have been found in the US.

Farmers are advised to include diversity in their cropping systems to reduce the potential of herbicide resistance. Using the right herbicide, at the right rate, at the right time, crop rotation and varying herbicide modes of action are tools that can be used to fight herbicide resistant weeds.

The full news release can be found on the Monsanto website.