Monsanto Canada Inc.

Monsanto Canada Inc.

March 31, 2010 11:00 ET

Glyphosate-Resistant Giant Ragweed Confirmed in Ontario

Ragweed population evaluated by University of Guelph research scientists is first finding of a glyphosate-resistant weed in Canada

WINNIPEG, MANITOBA--(Marketwire - March 31, 2010) - University of Guelph weed scientists have completed evaluations of a giant ragweed (Ambrosia trifida) population in Ontario and can now confirm the first case of a glyphosate-resistant weed in Canada.

"We have been able to demonstrate that plants from this population of giant ragweed meet all five requirements necessary to confirm resistance, including surviving increased rates of glyphosate and the ability to pass resistance along to the next generation," said Dr. François Tardif of the department of plant agriculture at the University of Guelph.

The population in question underwent both greenhouse and field testing by university researchers, working in conjunction with Monsanto Canada, in order to confirm resistance. While over 30 other species of weeds in Canada have developed resistance to herbicides, this is the first confirmation of a glyphosate-resistant weed in Canada. In other countries around the world, 17 weed species – including giant ragweed – have been confirmed as resistant to glyphosate. Ten of those species are in the United States. All of these glyphosate-resistant weed biotypes have been managed with other herbicides and cultural practices.

"Growers frequently use glyphosate as an important weed control tool so the appearance of a glyphosate-resistant population is an important reminder for growers to consider diversity in their weed management strategies and crop management practices," added Dr. Sikkema, a plant agriculture professor at the University of Guelph's Ridgetown Campus. "Fortunately, we have already been able to identify some options for this producer that will provide effective control in corn and wheat."

This finding is the result of research that began late in 2008 when the population was first brought to the attention of the University of Guelph researchers and Monsanto. The glyphosate-resistant population is limited to giant ragweed from a single field site. Dr. Sikkema is working directly with the affected grower on alternative strategies to manage this giant ragweed population.

As part of an ongoing collaborative research effort between the University of Guelph and Monsanto, other giant ragweed populations in southwestern Ontario are also being tested for their susceptibility to glyphosate. Results from these tests will help determine the scope of the issue and any need to adjust weed management strategies and recommendations. Dr. Sikkema advises growers to include diversity in their cropping systems. This includes a diverse crop rotation with multiple herbicide modes of action over time. Growers are advised to use appropriate rates and other herbicides in their program where possible, including existing residual herbicides, to reduce the likelihood of glyphosate resistance developing in their fields.

"There are definitely crop management practices that can increase the risk of resistant weeds developing. That is why we strongly recommend farmers scout their fields, follow sound crop rotation practices and use additional modes of action that complement the Roundup Ready® system to control problem weeds and reduce the likelihood of developing resistance," said Dr. Mark Lawton, Monsanto's technology development lead for Eastern Canada.

Monsanto takes product stewardship and claims of glyphosate resistance seriously and encourages growers to report suspected cases of resistance to Monsanto representatives so they can work with academics and extension services to investigate suspected cases, develop solutions for farmers and communicate the findings broadly. Monsanto's current best management practices include:

  • Start with a clean field by either utilizing a burn down herbicide or tillage to control weeds early.
  • Use Roundup Ready technology as the foundation of a total weed management program.
  • Add other herbicides or cultural practices where appropriate as part of the Roundup Ready cropping system.
  • Use the right herbicide rate at the right time.
  • Control weeds throughout the season and reduce the weed seed bank.
  • Rotation to other Roundup Ready crops will add opportunities for introduction of other modes of action.

Monsanto Canada is headquartered in Winnipeg, Manitoba. Monsanto Company is an agricultural company and a leading global provider of technology – focused on enabling both small-holder and large-scale farmers to produce more from their land while conserving more of world's natural resources such as water and energy. Learn more about our business and our commitments at

Monsanto Company is a member of Excellence Through StewardshipSM (ETS). Monsanto products are commercialized in accordance with ETS Product Launch Stewardship Guidance, and in compliance with Monsanto's Policy for Commercialization of Biotechnology-Derived Plant Products in Commodity Crops. This product has been approved for import into key export markets with functioning regulatory systems. Any crop or material produced from this product can only be exported to, or used, processed or sold in countries where all necessary regulatory approvals have been granted. It is a violation of national and international law to move material containing biotech traits across boundaries into nations where import is not permitted. Growers should talk to their grain handler or product purchaser to confirm their buying position for this product. Excellence Through StewardshipSM is a trademark of Excellence Through Stewardship.

Contact Information

  • Media inquiries should be directed to:
    Monsanto Canada Inc.
    Dr. Mark Lawton
    (519) 780-6606
    University of Guelph
    Dr. Peter Sikkema
    (519) 674-1603
    University of Guelph
    Dr. Francois Tardif
    (519) 824-4120 ext 53395