Winnipeg, Manitoba, Canada
November 15, 2010
Following up their work from last spring which confirmed the first finding of a glyphosate-resistant weed in Canada, University of Guelph weed scientists have now confirmed the presence of additional glyphosate-resistant populations in soybean fields in southwestern Ontario.
Greenhouse testing of seed samples collected from southwestern Ontario in the fall of 2009 showed that an additional 16 fields had populations of giant ragweed (Ambrosia trifida) resistant to glyphosate. As part of the ongoing research conducted by Dr. Francois Tardif and Dr. Peter Sikkema from the department of Plant Agriculture at the University of Guelph, giant ragweed seed was collected from 57 fields across Essex, Kent and Lambton Counties in 2009 in an attempt to document the distribution of glyphosate-resistant giant ragweed in Ontario. Samples collected from the 41 other fields were found to be effectively controlled with glyphosate and therefore, were not found to be resistant. All resistant populations from this survey were located in Essex County in southwestern Ontario.
"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. Tardif.
The populations in question underwent greenhouse testing by the 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, glyphosate-resistant giant ragweed continues to be the only weed to be confirmed as glyphosate-resistant in Canada. In other countries around the world, 20 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.
Much of the ongoing research work is rightly focused on identifying herbicide solutions for management of glyphosate resistant giant ragweed and giving farmers effective solutions for management and control.
"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," said Dr. Sikkema, "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."
Based on the field research conducted this past year, Eragon(TM) and FirstRate(TM) herbicide were the most effective commercial products for control of the glyphosate-resistant giant ragweed. "FirstRate worked well provided the population was not resistant to the Group 2 herbicides" said Dr. Sikkema, "unfortunately other postemergence herbicide options in soybeans such as Blazer(R), Reflex(R), Basagran(R), Liberty(R), Classic(R), Pursuit(R) and Pinnacle(R) and the soil applied herbicides Lorox(R), Sencor(R), Broadstrike(TM) RC, Pursuit(R) and Command(R) did not provide commercially acceptable control."
There were a few new experimental treatments in soybeans that also worked very well in controlling the glyphosate-resistant giant ragweed. "Use of dicamba with dicamba tolerant soybeans was one of those new treatments that was very effective in controlling glyphosate-resistant giant ragweed" said Dr. Sikkema. "We are encouraging companies to pursue some of these new management strategies in soybeans to expand our control options for this issue."
Dicamba tolerant soybeans are currently in Monsanto's research and development pipeline but are not expected to be commercially available until 2014.
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.
Farmers are constantly reminded to include diversity in their cropping systems to reduce the likelihood of glyphosate resistance materializing in their fields. This includes a diverse crop rotation with multiple herbicide modes of action over time. Farmers 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.
"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," explained Dr. Mark Lawton, Monsanto Canada's technology development lead for eastern Canada. "It is also important for the researchers to gather field history that may help explain the presence of this resistance in the impacted fields."
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(R) 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.
"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(R) system to control problem weeds and reduce the likelihood of developing resistance," added Dr. Lawton.
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