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Global herbicide-resistant weed populations continue rising due to selection pressures exerted by herbicides. Despite this, herbicides continue to be farmers’ preferred weed-control method due to cost and efficiency relative to physical or biological methods. However, weeds developing resistance to herbicides not only challenges crop production but also threatens ecosystem services by disrupting biodiversity, reducing soil health, and impacting water quality. Our objective was to develop a simulation model that captures the feedback between weed population dynamics, agricultural management, profitability, and farmer decision-making processes that interact in unique ways to reinforce herbicide resistance in weeds. After calibration to observed data and evaluation by subject matter experts, we tested alternative agronomic, mechanical, or intensive management strategies to evaluate their impact on weed population dynamics. Results indicated that standalone practices enhanced farm profitability in the short term but lead to substantial adverse ecological outcomes in the long term, indicated by elevated herbicide resistance (e.g., harm to non-target species, disrupting natural ecosystem functions). The most management-intensive test yielded the greatest weed control and farm profit, albeit with elevated residual resistant seed bank levels. We discuss these findings in both developed and developing-nation contexts. Future work requires greater connectivity of farm management and genetic-resistance models that currently remain disconnected mechanistically.
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Are Glyphosate‐Resistant Weeds a Threat to Conservation Agriculture? Evidence from Tillage Practices in Soybeans
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 resistance becomes more widespread and more farmers turn to tillage for supplemental weed control.
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- Award ID(s):
- 1832042
- PAR ID:
- 10277358
- Date Published:
- Journal Name:
- American Journal of Agricultural Economics
- ISSN:
- 0002-9092
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1111/ajae.12243
