Photo: Kochia, southwest Montana. © 2020 Delena Norris-Tull
Effectiveness of herbicides in agricultural lands
Summaries of the research and commentary by Dr. Delena Norris-Tull, Professor Emerita of Science Education, University of Montana Western, September 2020.
Schulz and Segobye, 2016, point out that, “The importance of weed control using herbicides cannot be overestimated. The yield loss potential among all crops without weed control is about 37% …Through the use of effective herbicides, these losses have been reduced to about 9% through all cropping systems. Nevertheless, this still means that global agriculture is suffering yield losses worth at least $300 billion each year… Weed control without effective herbicide programs would substantially increase the cost of production, as the input of manual labor would need to be increased. In addition to higher production costs, farmers would also see reduced soil health, greenhouse gas emission and increased soil erosion, as effective no-till agriculture would be nearly impossible.”
Herbicide application is complex. Herbicide applications have to be carefully timed, to increase their effectiveness. For example, rainfall within 1-24 hours after application can reduce the effectiveness of various herbicides, and different plant species respond differentially to the timing of rainfall after application (Bovey, et al., 1990). The effectiveness of herbicide application also varies by species, depending on the growth stage of the target plant (Engle & Bowman, 1980). This means that research has to be conducted, on each herbicide, or combination of herbicides, that is likely to be used on a particular species of plant. Without that research, the cost of using herbicides increases dramatically, and the likelihood of unintended consequences, such as herbicide drift, the development of herbicide-resistant weeds, or herbicide contamination of land and waterways, also increases.
There is a multitude of research on the effectiveness of the various herbicides that have been used over the decades. But much of that research loses its usefulness in the presence of two factors that now override all the effectiveness data: the evolution of herbicide resistance in noxious weeds, and the growing appreciation for the detrimental effects, to human health or to the environment, of the long-term use of herbicides.
In additional sections, I include some of the research on a number of the most frequently used herbicides, such as 2,4-D and glyphosate. This is not an exhaustive review of all the research reports, but I attempt to highlight some of the most important information.
Much of the current research (particularly research from 2000 to 2020) on the effectiveness of herbicides in farmlands focuses on methods to prevent or slow down the evolution of herbicide resistance in noxious weeds. Refer to the section on Herbicide Resistance for descriptions of some of that research, as it provides summaries of the best management practices for preventing herbicide resistance.
Within this website, the section, Innovative Solutions, includes detailed discussion of the research on agricultural best practices. Unfortunately, the advent of herbicide resistance noxious weeds has caused farmers to rethink agricultural best practices. In particular, conservation tillage is much more challenging in the presence of noxious weeds that have become resistant to multiple types of herbicides. The best management practices for preventing/slowing the evolution of herbicide resistance in weeds now overshadows the previously considered agricultural best practices.
Farmland is land that is regularly disturbed. Both native and non-native species can become a problem, and can attain the label “noxious weeds,” when they are more effective at growing within that disturbed land than the desired crops. Refer to the sections Why we need plants and Native plants for more information on the role of plants, even so-called weeds, in ecological systems. Because the land is regularly disturbed, either by the removal of the crop at harvest time, or by tilling the land after harvest or before planting, non-crop plants are constantly trying to do their job – the job of conserving the soil and restoring needed nutrients to the soil. Some crops even become weedy themselves, and create challenges when they invade wildlands or contaminate the seed stock of the original crop.
As long as farmland is regularly disturbed, farmers will have to deal with the removal of unwanted plants.
References:
Links to additional information on herbicides and other pesticides:
Effectiveness of herbicides in agricultural lands
Summaries of the research and commentary by Dr. Delena Norris-Tull, Professor Emerita of Science Education, University of Montana Western, September 2020.
Schulz and Segobye, 2016, point out that, “The importance of weed control using herbicides cannot be overestimated. The yield loss potential among all crops without weed control is about 37% …Through the use of effective herbicides, these losses have been reduced to about 9% through all cropping systems. Nevertheless, this still means that global agriculture is suffering yield losses worth at least $300 billion each year… Weed control without effective herbicide programs would substantially increase the cost of production, as the input of manual labor would need to be increased. In addition to higher production costs, farmers would also see reduced soil health, greenhouse gas emission and increased soil erosion, as effective no-till agriculture would be nearly impossible.”
Herbicide application is complex. Herbicide applications have to be carefully timed, to increase their effectiveness. For example, rainfall within 1-24 hours after application can reduce the effectiveness of various herbicides, and different plant species respond differentially to the timing of rainfall after application (Bovey, et al., 1990). The effectiveness of herbicide application also varies by species, depending on the growth stage of the target plant (Engle & Bowman, 1980). This means that research has to be conducted, on each herbicide, or combination of herbicides, that is likely to be used on a particular species of plant. Without that research, the cost of using herbicides increases dramatically, and the likelihood of unintended consequences, such as herbicide drift, the development of herbicide-resistant weeds, or herbicide contamination of land and waterways, also increases.
There is a multitude of research on the effectiveness of the various herbicides that have been used over the decades. But much of that research loses its usefulness in the presence of two factors that now override all the effectiveness data: the evolution of herbicide resistance in noxious weeds, and the growing appreciation for the detrimental effects, to human health or to the environment, of the long-term use of herbicides.
In additional sections, I include some of the research on a number of the most frequently used herbicides, such as 2,4-D and glyphosate. This is not an exhaustive review of all the research reports, but I attempt to highlight some of the most important information.
Much of the current research (particularly research from 2000 to 2020) on the effectiveness of herbicides in farmlands focuses on methods to prevent or slow down the evolution of herbicide resistance in noxious weeds. Refer to the section on Herbicide Resistance for descriptions of some of that research, as it provides summaries of the best management practices for preventing herbicide resistance.
Within this website, the section, Innovative Solutions, includes detailed discussion of the research on agricultural best practices. Unfortunately, the advent of herbicide resistance noxious weeds has caused farmers to rethink agricultural best practices. In particular, conservation tillage is much more challenging in the presence of noxious weeds that have become resistant to multiple types of herbicides. The best management practices for preventing/slowing the evolution of herbicide resistance in weeds now overshadows the previously considered agricultural best practices.
Farmland is land that is regularly disturbed. Both native and non-native species can become a problem, and can attain the label “noxious weeds,” when they are more effective at growing within that disturbed land than the desired crops. Refer to the sections Why we need plants and Native plants for more information on the role of plants, even so-called weeds, in ecological systems. Because the land is regularly disturbed, either by the removal of the crop at harvest time, or by tilling the land after harvest or before planting, non-crop plants are constantly trying to do their job – the job of conserving the soil and restoring needed nutrients to the soil. Some crops even become weedy themselves, and create challenges when they invade wildlands or contaminate the seed stock of the original crop.
As long as farmland is regularly disturbed, farmers will have to deal with the removal of unwanted plants.
References:
- Bovey, R.W., Meyer, R.E., & Whisenant, S.G. (1990). Effect of simulated rainfall on herbicide performance in Huisache (Acacia farnesiana) and Honey Mesquite (Prosopis glandulosa). Weed Technology, 4:26-30.
- Engle, D.M., & Bonham, C.D. (Sep., 1980). Nonstructural carbohydrates in roots of Gambel Oak sprouts following herbicide treatment. Journal of Range Management, 33 (5): 390-394.
- Schulz, B., & Segobye, K. (2016). 2,4-D transport and herbicide resistance in weeds. Journal of Experimental Botany, 67 (11):3177-3179. doi: 10.1093/jxb/erw199
Links to additional information on herbicides and other pesticides: