Glyphosate resistant weed found in Ontario

by BRIAN LOCKHART
 
A small patch of giant ragweed in an isolated field in southwestern Ontario came to the attention of research scientists when a local crop farmer’s efforts to eliminate it failed.

“This is the first weed that has been confirmed as having a resistance to glyphosate in Canada,” says Dr. Mark Lawton, Monsanto Canada technology research lead for Eastern Canada.

But varieties of the weed have already proven to be resistant to the herbicide in the United States, he says.

Monsanto, an international agricultural products company, created the glyphosate molecule in the 1970s. It is the active ingredient in Roundup, the company’s systemic, broad-spectrum herbicide as well as in other brand name herbicides. The company has also developed the genetic technology to make certain crops resistant to glyphosate applications. In soybeans alone, Roundup Ready resistance varieties now make up more than 60 per cent of Ontario’s annual crop.

Rachelle Byl, horticultural sales specialist at Cardinal Farm Supply in Alliston, says glyphosate represents around 50 per cent of the weed control products they sell to the south central Ontario market.

Giant ragweed is native to North America and can reach a height of three metres if left unchecked. In Ontario it is predominantly found in the southwest.

“It’s a fairly common weed in corn and soybean growing areas,” says Dr. Peter Sikkema, plant agriculture professor at the University of Guelph’s Ridgetown campus.

Sikkema says the farmer contacted the university in the summer of 2008 after noticing he had “poor control with glyphosate.”

The university has researched giant ragweed control in corn and soybean production for several years.

The discovery of glyphosate resistant plants would be a “significant concern to the individual farmer who has it,” Sikkema says, especially if the aim is to control it in a soybean field.

There are good options to control the weed in corn and cereals, such as wheat, he explains: “But in soybeans we really don’t have alternative herbicides that provide effective control to the growers.”

Not all giant ragweed will be glyphosate resistant, he adds. “They are different bio-types. One plant will be susceptible and one will be resistant.”

University researchers have collected seed samples of the weed from 50 locations in the Essex County area, including the location where the glyphosate resistant type was found. Results from this study will be released in about a month, Sikkema says.

Lawton says building diversity into weed management strategy, is a good preventative practice to avoid agronomic challenges. Diversity can be achieved “through several methods including herbicides, tillage, and crop rotation,” he says. BF