Photo: Lamb's-quarters. © 2020 Delena Norris-Tull
Best management practices for preventing the development of herbicide-resistant weeds
Summaries of the research and commentary by Dr. Delena Norris-Tull, Professor Emerita of Science Education, University of Montana Western, October 2020.
Dong, et al., 2016, developed a tool to evaluate the extent to which farmers adopt various best management practices for preventing the development of herbicide-resistant weeds. They created a survey that included questions about the following best management practices:
For each question, the farmer was asked to respond with the extent to which they have adopted that strategy by choosing: always, often, sometimes, rarely, or never.
After telephone interviews with 402 soybean farmers, 402 corn farmers, and 401 cotton farmers, Dong, et al., 2016, analyzed the data. The purpose of the survey was to improve the tool used to examine the extent to which farmers adopt the best management practices.
Overall results of the survey: The three least adopted practices were: cleaning equipment prior to moving it (often or always = 25.6%); supplementing herbicides with tillage (often or always = 21%); and using multiple herbicide modes of action (often or always = 38.8%). The three most often adopted practices were using weed-free seed (always = 87.5%); following the recommended herbicide application rate (always = 74.4%); starting with a clean field (always = 60.6%) (Dong, et al., 2016).
Dong, et al., 2016, discovered somewhat different responses from farmers growing different crops.
Results for soybean farmers, Dong, et al., 2016: The three least adopted practices were: cleaning equipment prior to moving it (often or always = 20.6%); supplementing herbicides with tillage (often or always = 15.4%); and using multiple herbicide modes of action (often or always = 28.2%). The two most often adopted practices were using weed-free seed (always = 91.3%); following the recommended herbicide application rate (always = 74.4%).
Results for corn farmers, Dong, et al., 2016: The three least adopted practices were: cleaning equipment prior to moving it (often or always = 17.8%); supplementing herbicides with tillage (often or always = 22.0%); and using multiple herbicide modes of action (often or always = 49.6%). The two most often adopted practices were using weed-free seed (always = 89.4%); following the recommended herbicide application rate (always = 72.2%).
Results for cotton farmers, Dong, et al., 2016: The three least adopted practices were: cleaning equipment prior to moving it (often or always = 38%); supplementing herbicides with tillage (often or always = 25.5%); and using multiple herbicide modes of action (often or always = 38.5%). The two most often adopted practices were using weed-free seed (always = 81.9%); following the recommended herbicide application rate (always = 76.5%).
Cotton farmers adopted more strategies than the other farmers. They had the highest ratings for each the following strategies: scout fields before applying herbicides (often or always = 86.0%); scout fields after applying herbicides (often or always = 83.4%); start with a clean field (often or always = 79.9%); control weeds early when small (often or always = 92%); control weed escapes and prevent seed setting (often or always = 81.9%) (Dong, et al., 2016).
Dong, et al., 2016, also recorded quite a bit of information about each farmer, including their level of education, years in farm management, and farm yield. They concluded that many farmers had not been aware of the best management practices, thus, they consider educating farmers about these practices as crucial to achieving the goal of reducing the evolution of herbicide-resistant weeds. While some of the practices would have a negative economic impact for farmers, a number of them would be relatively easy to implement.
Herbicide resistance has created a problem in so many crops that many farmers are reverting back to traditional tillage, rather than conservation tillage. Many others are reverting back to hand-pulling weeds. Ron Smith, 2013, adds to the list of best management practices, advocating for, in addition to the use of pre-plant or pre-emergent herbicide, a residual herbicide and a postemergence herbicide (article by Ron Smith, Herbicide resistance changing Sunbelt production options, Southeast Farm Press, April 3, 2013). However, the use of multiple herbicides leads to additional costs and potential concerns about residual herbicide remaining in the soil.
As the survey conducted by Dong, et al., 2016, reveals, too few farmers are adopting the “best management practices” for preventing the development of herbicide-resistant weeds. In addition, while the study by Meyer, et al., 2015, is a thorough and much needed type of study, a two-year study is not long enough to determine the longer-term impacts of the treatments that were tested.
We do not yet have enough evidence to tell us how effective these practices will be in the long run.
Australian Management of Superweeds
Western Australia, which has low rainfall, is now considered the "superweed capital of the world." Blatt, 2020, reported that the Australian Herbicide Resistance Initiative, which teams up farmers and scientists, developed the following recommendations: mix and rotate different weaker herbicides; use different combinations of chemicals and switch them up annually. However, this has had only short-term benefits, and the use of multiple herbicides can be more expensive. The Australian farmers are now trying the strategy of capturing and destroying weed seeds, called the "Harvest Seed Weed Control." One strategy they are using is to concentrate and burn seed chaff in a narrow window. "The burning process kills the vast majority of weed seeds (Blatt, 2020). Other strategies, known as chaff tramlining and chaff lining, are similar in concept: weeds seeds are concentrated in lines to they don't contaminate crops."
References:
Next Sections on Herbicides and other Pesticides:
Best management practices for preventing the development of herbicide-resistant weeds
Summaries of the research and commentary by Dr. Delena Norris-Tull, Professor Emerita of Science Education, University of Montana Western, October 2020.
Dong, et al., 2016, developed a tool to evaluate the extent to which farmers adopt various best management practices for preventing the development of herbicide-resistant weeds. They created a survey that included questions about the following best management practices:
- Scout fields before and after applying herbicides. Scouting is a technique of walking systematically through fields and recording each weed species, its location and numbers.
- Start with a clean field, either by using a burndown herbicide or tillage. The survey asked the percentage of farmland treated with a pre-plant burndown herbicide.
- Control weeds while they are still small.
- Control weed escapes and prevent them from setting seeds. (Research has indicated that reduction of the weed seed-bank can effectively reduce the use of herbicides).
- Clean equipment before moving it from field to field.
- Use weed-free seed.
- Use multiple herbicides with multiple modes of action. The survey asked the percentage of land that received pre-emergent residual herbicides.
- Use tillage to supplement herbicide applications.
- Use the herbicide recommended application rate.
- Use crop rotations. In particular, rotate between a RoundUp Ready crop and a non-RoundUp Ready crop. Crop rotation is helpful for reducing weeds, and thus reducing the amount of herbicide used. The survey asked for the percentage of land planted in each crop.
For each question, the farmer was asked to respond with the extent to which they have adopted that strategy by choosing: always, often, sometimes, rarely, or never.
After telephone interviews with 402 soybean farmers, 402 corn farmers, and 401 cotton farmers, Dong, et al., 2016, analyzed the data. The purpose of the survey was to improve the tool used to examine the extent to which farmers adopt the best management practices.
Overall results of the survey: The three least adopted practices were: cleaning equipment prior to moving it (often or always = 25.6%); supplementing herbicides with tillage (often or always = 21%); and using multiple herbicide modes of action (often or always = 38.8%). The three most often adopted practices were using weed-free seed (always = 87.5%); following the recommended herbicide application rate (always = 74.4%); starting with a clean field (always = 60.6%) (Dong, et al., 2016).
Dong, et al., 2016, discovered somewhat different responses from farmers growing different crops.
Results for soybean farmers, Dong, et al., 2016: The three least adopted practices were: cleaning equipment prior to moving it (often or always = 20.6%); supplementing herbicides with tillage (often or always = 15.4%); and using multiple herbicide modes of action (often or always = 28.2%). The two most often adopted practices were using weed-free seed (always = 91.3%); following the recommended herbicide application rate (always = 74.4%).
Results for corn farmers, Dong, et al., 2016: The three least adopted practices were: cleaning equipment prior to moving it (often or always = 17.8%); supplementing herbicides with tillage (often or always = 22.0%); and using multiple herbicide modes of action (often or always = 49.6%). The two most often adopted practices were using weed-free seed (always = 89.4%); following the recommended herbicide application rate (always = 72.2%).
Results for cotton farmers, Dong, et al., 2016: The three least adopted practices were: cleaning equipment prior to moving it (often or always = 38%); supplementing herbicides with tillage (often or always = 25.5%); and using multiple herbicide modes of action (often or always = 38.5%). The two most often adopted practices were using weed-free seed (always = 81.9%); following the recommended herbicide application rate (always = 76.5%).
Cotton farmers adopted more strategies than the other farmers. They had the highest ratings for each the following strategies: scout fields before applying herbicides (often or always = 86.0%); scout fields after applying herbicides (often or always = 83.4%); start with a clean field (often or always = 79.9%); control weeds early when small (often or always = 92%); control weed escapes and prevent seed setting (often or always = 81.9%) (Dong, et al., 2016).
Dong, et al., 2016, also recorded quite a bit of information about each farmer, including their level of education, years in farm management, and farm yield. They concluded that many farmers had not been aware of the best management practices, thus, they consider educating farmers about these practices as crucial to achieving the goal of reducing the evolution of herbicide-resistant weeds. While some of the practices would have a negative economic impact for farmers, a number of them would be relatively easy to implement.
Herbicide resistance has created a problem in so many crops that many farmers are reverting back to traditional tillage, rather than conservation tillage. Many others are reverting back to hand-pulling weeds. Ron Smith, 2013, adds to the list of best management practices, advocating for, in addition to the use of pre-plant or pre-emergent herbicide, a residual herbicide and a postemergence herbicide (article by Ron Smith, Herbicide resistance changing Sunbelt production options, Southeast Farm Press, April 3, 2013). However, the use of multiple herbicides leads to additional costs and potential concerns about residual herbicide remaining in the soil.
As the survey conducted by Dong, et al., 2016, reveals, too few farmers are adopting the “best management practices” for preventing the development of herbicide-resistant weeds. In addition, while the study by Meyer, et al., 2015, is a thorough and much needed type of study, a two-year study is not long enough to determine the longer-term impacts of the treatments that were tested.
We do not yet have enough evidence to tell us how effective these practices will be in the long run.
Australian Management of Superweeds
Western Australia, which has low rainfall, is now considered the "superweed capital of the world." Blatt, 2020, reported that the Australian Herbicide Resistance Initiative, which teams up farmers and scientists, developed the following recommendations: mix and rotate different weaker herbicides; use different combinations of chemicals and switch them up annually. However, this has had only short-term benefits, and the use of multiple herbicides can be more expensive. The Australian farmers are now trying the strategy of capturing and destroying weed seeds, called the "Harvest Seed Weed Control." One strategy they are using is to concentrate and burn seed chaff in a narrow window. "The burning process kills the vast majority of weed seeds (Blatt, 2020). Other strategies, known as chaff tramlining and chaff lining, are similar in concept: weeds seeds are concentrated in lines to they don't contaminate crops."
References:
- Blatt, T. (Winter, 2020). Superweed saga: Australia’s creative tools to fight herbicide-resistant weeds. In Harvard International Review, vol. 41, A quiet desperation: Modern agriculture and rural life, pp. 48-50.
- Dong, F., Mitchell, P.D., Hurley, T.M., & Frisvold, G.B. (2016). Quantifying adoption intensity for weed-resistance management practices and its determinants among U.S. soybean, corn, and cotton farmers. Journal of Agricultural and Resource Economics, 41(1):42-61. DOI:10.22004/ag.econ.230770
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