Are glyphosate‐resistant weeds a threat to conservation agriculture? Evidence from tillage practices in soybeans

Abstract

Conservation tillage in American soybean production has become increasingly common, improving soil health while reducing soil erosion and fuel consumption. This trend has been reinforced by the widespread adoption of glyphosate-based weed control systems. Many weed species have since evolved to resist glyphosate, reducing its effectiveness. We provide evidence that the spread of glyphosate-resistant weeds is responsible for significant reductions in the use of conservation tillage in soybean production. We estimate reduced-form and structural probit models of tillage choice, using a large panel of field-level soybean management decisions from across the United States spanning 1998-2016. We find that the first emergence of glyphosate-resistant weed species has little initial effect on tillage practices, though by the time that eight glyphosate-resistant weed species are identified, conservation tillage and no-till use fall by 3.9 percentage points and 7.6 percentage points, respectively. We further find that when ten glyphosate-resistant species are present, the predicted adoption rate of non-glyphosate herbicides rises 50 percentage points, and that the availability of non-glyphosate herbicides facilitates continued use of conservation tillage as glyphosate-resistant weeds proliferate. Using a simple benefits transfer model, we conservatively estimate that between 2008 and 2016 farmers' tillage responses to the spread of glyphosate-resistant weeds have caused water quality and climate damages via fuel emissions valued at nearly $245 million. This value does not account for climate damages due to carbon released during soil disruptions and is likely to grow as glyphosate

Insecticides, more than herbicides, land use, and climate, are associated with declines in butterfly species richness and abundance in the American Midwest

“…The area-treatment measure based on broad practice classes is consistent with recent empirical results on patterns of substitution and complementarity in pest control markets 24,32,33 , allowing deeper insights into how changes in pesticide markets or policy might affect the overall threat to specific insect populations.…”

“…Crop Reporting Districts (CRDs) level and link this measure to county-level cropland land cover data to derive an annual county-level area-treatment metric. The area-treatment measure based on broad practice classes is consistent with recent empirical results on patterns of substitution and complementarity in pest control markets 24,32,33 , allowing deeper insights into how changes in pesticide markets or policy might affect the overall threat to specific insect populations.…”

Ectopic expression of a rice triketone dioxygenase gene confers mesotrione tolerance in soybean

“…Selective herbicides were major contributors to improve crop production before the deployment of herbicide‐tolerant (HT) crops 2,3 . The cultivation of HT crops coupled with the application of corresponding herbicides can effectively manage weeds, improve crop productivity and quality, enhance the content of soil organic matter, improve soil health, and reduce fuel consumption and emission by reducing tillage 2–5 …”

“…2,3 The cultivation of HT crops coupled with the application of corresponding herbicides can effectively manage weeds, improve crop productivity and quality, enhance the content of soil organic matter, improve soil health, and reduce fuel consumption and emission by reducing tillage. [2][3][4][5] Deployment of glyphosate tolerant (GT) crops, alongside application of glyphosate, revolutionized modern agriculture by providing an effective alternative to using traditional selective herbicides for weed control. 6 GT crops were the most rapidly adopted technology in the history of agriculture, which was primarily due to the nonselective, very effective, and relatively inexpensive nature of glyphosate.…”

Soil Health: New Opportunities to Innovate in Crop Protection Research and Development

“…Still, the relationship between crop protection innovation and soil health is rarely discussed. An exception to this is weed management, for two reasons: reverting to tillage to manage herbicide resistant weeds would directly reduce soil health (Nunes et al, 2020;Van Deynze et al, 2021) and practices that promote soil health can positively contribute to weed management, e.g., cover cropping (Osipitan et al, 2018).…”