This past summer I had the opportunity to work for Bayer Crop Science, working closely with growers helping them make decisions on their farm regarding the use of herbicides. Part of the training on my part required me to have a deep understanding of the importance of tank mixing, rotation of active ingredients, and proper application of the chemicals. Most growers understand these topics, but you always seem to have the odd grower that couldn’t understand why the consistent use of the same chemical year after year was now much less effective and would blame the chemical companies first. Using the same chemicals every year is basically selecting for herbicide-resistant weeds by killing the non-resistant weeds and allowing the resistant weeds to go to seed and reproduce. This has led me to be very concerned about the growing number of resistant weeds in Canada, and the lack of policy around the issue.
What is Herbicide Resistance?
Herbicide resistance is when a plant inherits the ability to survive and set seed after what should have been a lethal dose of herbicide (Jones, 2019). After a plant is not killed by the herbicide, it will set seed that is not necessarily one hundred percent resistant but definitely has the traits for resistance. This process will continue if these weeds are hit with the same herbicides. The plants that are resistant to the herbicide will survive and set seed, and the weed population will increase. Learn more about herbicide groups here.
Resistance develops when the same herbicide or a herbicide from the same group is used repeatedly, and back to back. If a monoculture is grown, with a tight crop rotation, the same herbicide tends to be used frequently. A tight crop rotation refers to a crop being grown every two or three years in the same field. Annual weeds such as foxtail tend to develop resistance due to the high number of seeds produced. Interestingly enough, resistance tends to develop with herbicides that are the most efficient. This is due to the herbicide intensely selecting for resistance in the weed species that they are controlling (Martin, 2020).
Dealing with Herbicide Resistance
Herbicide resistance has been increasing steadily since 1975, as you can see in the first graph titled “Increase in unique resistant weed cases in Canada”. As of 2018, there are currently 76 cases of unique resistant weeds in Canada. In the prairies, Alberta has 23 cases, Saskatchewan has 22, and Manitoba has 30. In the 2014-15 Saskatchewan Weed Survey, Dr. Beckie, a Herbicide-Resistant Plants Research Scientist for Agriculture and Agri-Food Canada found that 227 out of 400 fields, or 57% had Group 1 or 2 resistant weeds present. In the 2016 Manitoba survey, 102 out of 151 fields, or 68% of the fields had Group 1 or 2 herbicide-resistant weeds. A recent survey on Alberta weed resistance was not available (Beckie, The State of Herbicide Resistance in Western Canada, 2018).
Wild oats are one of the most concerning weeds with resistance, and as you can see from the map titled “Group 1 resistant wild oat”, there is a large concentration of cases throughout the prairies. While this map only shows the cases of Group 1 resistance, there are a growing number of cases of Group 1 and 2 resistant wild oats. In the 2014 Saskatchewan Weed Survey, Group 1 and 2 resistant wild oats were found in 25% of fields, an increase from 5% in 2009. This increase is happening due to growers using Group 2 chemicals to deal with Group 1 resistance. In the 2016 Manitoba Weed Survey, Group 1 and 2 resistant wild oats were found on 42% of fields, up from 13% in 2008. Multiple resistance is concerning to see because this means that Group 2, a Group typically used to deal with Group 1 resistance, is now losing its effectiveness (Beckie, The State of Herbicide Resistance in Western Canada, 2018).
Total acres with resistance present have gone from 10.9 million acres in 1995 to approximately 38 to 40 million acres in 2017 across the prairies. Total cultivated acres in Western Canada is 70 million acres, meaning that over half the acres have herbicide-resistant weeds. You can see a breakdown of the number of acres with each resistant group above in the table titled “Estimated field area on the Canadian prairies (acres) impacted by herbicide-resistant weeds 2007-2009”. This is very important as this shows that along with the rising cases of resistant weeds, the amount of area affected is also very large, the problem isn’t just concentrated bubbles of herbicide-resistant weeds (Beckie, The State of Herbicide Resistance in Western Canada, 2018).
Australia is dealing with the costs of herbicide-resistant weed populations by having to spend 27 percent more per acre to cover management costs and yield loss. In the US, growers are forced to pay to have their fields hand weeded (Bayer Crop Science Canada, 2019). This is a very expensive option and is a last resort. Canada is third on the list for the most herbicide-resistant weeds, so although we don’t have this high of increased costs yet, farmers are already seeing around $11 to $12/acre to manage weed resistance. At this point, our best herbicide-resistant weed management practices are crop diversity, competitive crops, tank mixing herbicides, rotating herbicide groups, rotating in-crop wheat and non-wheat herbicides, weed sanitation practices, specific weed management for each field, strategic tillage, and accurate records (H.J. Beckie, 2018). More detailed information on best management practices can be found here.
Zero Tolerance Policy for Herbicide Resistance
Companies like Bayer Crop Science are already coming out with initiatives such as Mix It Up, where they will pay you to use competitor’s chemicals to change up your herbicide groups (Bayer Crop Science, 2020). More information about Bayer’s Mix It Up program can be found here. This is a great start but it is far from enough. I would propose that there be a national policy focused on managing our current level of resistance, and ensuring that the level of resistance does not rise to the levels seen in Australia or the U.S. The first step would be to push for more grower awareness and training for proper rotations of chemicals. Like the rewards programs that Bayer has for growers, there could also be a general rewards programs for farmers that take the initiative and report the various chemicals that they use, and also any resistance that they are seeing. This would help to crack down on new cases of resistance as they happen. This could also lead to a government agency having the ability to work with growers to stop the resistance from spreading, such as having workers come and hand weed the area, or giving advice and chemicals to the farmer on how to deal with the problem. The last part would be to reinforce this policy. While the problem directly affects the grower’s field that the weeds are in, this problem can and will spread. There would have to be checks and fines in place to crack down and punish farmers who refuse to mix up their chemicals.
Herbicide resistance is a growing problem in Canada, and if we don’t crack down on it, we will have the same high-cost problems that Australia and the U.S. have. There are many effective management practices to deal with the weeds, but there will need to be official policy and funding. I would propose a policy that focuses on informing growers about effective management, rewards and helps farmers that show good management, and last resort punishes growers who don’t deal with resistance effectively.