Monsanto recently announced that glyphosate-resistant giant ragweed had been identified in more soybean fields near Windsor. Until a small number of plants had been identified one field in 2008, Ontario has not had any glyphosate-resistant weeds.
The first case of what was then a suspected case of glyphosate-resistant giant ragweed was found in 2008 by the University of Guelph, and confirmed in 2009. The resistant plants were found in a field in Essex County, near Windsor, Ontario.
Follow-up this summer has found the glyphosate-resistant ragweed in 16 fields out of 57 tested, Monsanto confirmed in a press release. All identified cases were located in Essex County. Speaking for Monsanto from the Winnipeg office, Dr. Mark Lawton reassured farmers who plant Monsanto's roundup ready soy beans, saying “With the 2010 field research findings, we have a plan in place to follow-up with the growers in order to relay the findings and more importantly, suggest solutions for control. It is also important for the researchers to gather field history that may help explain the presence of this resistance in the impacted fields.”
The two University of Guelph researchers who originally found the glyphosate-resistant giant ragweed announced their find in 2009 in a press release said the find was significant because it was the first instance of glyphosate-resistant weeds in Canada.
It is believed the giant ragweed is the only weed species in Canada that is resistant to Roundup. In comparison, the United States has about 15 different weed species exhibiting resistance to glyphosate.
Roundup is Monsanto's trademark glyphosate-based herbicide. Monsanto has created a number of different crop seeds that are genetically modified to tolerate Roundup, including corn (maize), cotton, canola, and soy beans. The company is currently working on creating a Roundup-ready strain of wheat.
Speaking about this year's findings, Sikkema said "We know that farmers view glyphosate as an important weed control tool so the appearance of glyphosate-resistant populations and solutions to address this challenge are an important area of research for us and the farmers who have been impacted. Where crop rotation occurs, familiar herbicides such as 2.4-D in winter wheat and dicamba based herbicides in corn are very effective at controlling these glyphosate-resistant populations of giant ragweed. Our current research is focused on solutions to manage these populations in soybean production.”
The University of Guelph researchers explained last year "Resistance evolves after a weed population has been subjected to intense selection pressure in the form of repeated use of a single herbicide. The herbicide controls all the susceptible weeds, leaving only those with a resistant gene to reproduce."
According to Sikkema, the identification of the glyphosate-resistant giant ragweed is "... a very serious situation. In other jurisdictions, most glyphosate-resistant weed biotypes have been effectively managed with other herbicides and cultural practices. We’ll continue our research so we can make recommendations to growers on effective control options."
When it comes to dealing with the glyphosate-resistant giant ragweed, Monsanto's spokesperson said "There are definitely some 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.”
Monsanto recommends a number of steps to fight the resistant weed in Ontario. In the United States, Monsanto has started a program it calls the Roundup Ready Plus platform, which gives a small rebate to farmers for having to use other herbicides to combat glyphosate-resistant weeds. Monsanto also loosened restrictions on its patented technology, allow farmers to use herbicides made by two other companies in order to combat glyphosate resistance.
Until the giant ragweed developed resistance to glyphosate, the plant was known as "the worst nightmare" for those who suffer from hayfever.
It is thought that glyphosate-resistant giant ragweed is slower to spread than other resistant weeds found in the United States, such as Palmer Pigweed and horseweed, reported Delta Farm Press earlier this year.
In Ontario, at least 43 plant species have been identified as being resistant to herbicides, reported OMAFRA in 2009.
Monsanto has a weed management strategy posted on its website for those wishing to learn more about managing glyphosate-resistant species.