By Joe Hollis, Katie Dentzman, and J. Arbuckle
We can define herbicide resistance (HR) as the genetic adaptation of weeds to withstand herbicide applications (Owen et al. 2015). The threat of HR is fast becoming a significant threat to US agriculture, with many chemical treatments becoming less effective, threatening yields and profitability (Gould, Brown, and Kuzma 2018). It is likely that farmers will need to adjust their management practice to address the issue. However, little social science research has examined farmer perspectives regarding the threat of HR weeds and potential adaptive management practices. This report examines multiple years of data from the Iowa Farm and Rural Life Poll (IFRLP), an annual survey of Iowa farmers, to investigate how farmers’ attitudes and behaviors related to HR have changed over time.1
Current experiences, concerns, and management towards HR weeds
The 2022 IFRLP presented a series of statements on farmers' concerns, experiences, and management approaches to HR weeds. Eighty-seven percent of respondents indicated that they were concerned about HR weeds spreading to their farm operation from nearby farms (table 1). Furthermore, 85% reported making more than one herbicide application to a single crop in the previous five years. A similar percentage (84%) had made a change to their weed management program over the last five years due to concern about HR weeds on their farm, and around two-thirds (66%) reported changing management programs due to the actual presence of HR weeds on their farm. Approximately two-thirds (67%) also reported finding weeds suspected to be resistant to a single herbicide mode of action, and 8% reported finding weeds suspected of being resistant to multiple herbicide modes of action. A somewhat high proportion (22%) answered that they did not know if they had weeds that were resistant to multiple herbicide modes of action.
| Yes | No | Don’t Know | |
|---|---|---|---|
| Are you concerned about herbicide-resistant weeds spreading to your farm operation from nearby farms? | 87% | 10% | 3% |
| In the last five years have you made more than one herbicide application to a single crop in a single season? | 85% | 14% | 1% |
| Over the last five years, have you changed your weed management program due to CONCERN about herbicide-resistant weeds on your farm? | 84% | 14% | 2% |
| Have you found any weeds that you suspect are resistant to a single herbicide (i.e., single herbicide site of action) in fields that you farm? | 67% | 25% | 8% |
| Over the last five years, have you changed your weed management program due to the actual PRESENCE of herbicide-resistant weeds on your farm? | 66% | 30% | 4% |
| Have you found any weeds that you suspect are resistant to multiple herbicides (i.e., multiple herbicide sites of action) in any of the fields that you farm? | 28% | 50% | 22% |
Have farmers’ attitudes towards technologies and management practices changed over time?
In 2014 and 2022 farmers were asked to rate their agreement on a five-point scale from “strongly disagree” to “strongly agree” on a series of statements linked to attitudes toward technologies and management practices. Table 2 summarizes the differences between those who agreed or strongly agreed to each statement in both years. Notably, agreement between the years remained stable. Only three items differed by more than 5%. Farmers were less likely in 2022 to agree that when new pest management technologies are introduced, it is only a matter of time before pests evolve resistance (73%). In 2014, this number had been 82%. Similarly, concern towards the impact of pesticides on beneficial insects and microorganisms had reduced to 66% in 2022 compared to 74% in 2014. Finally, farmers’ belief that premature evolution of resistant pests could be attributed to poor management by a few farmers declined from 69% in 2014, to 61% in 2022. Two statements about future pest management technologies allaying current concern stood out for their very low levels of agreement. Most farmers did not agree with items proposing that Bt-resistant insect pests and herbicide-resistant weeds were not a concern “because new technologies will be developed to manage them.” In other words, they were not confident that new technologies will be sufficient to address the problem.
| 2014 | 2022 | |
|---|---|---|
| Attitudes toward technologies | ||
| I feel like pest (weed, disease, and insect) management is a never-ending technology treadmill. | 91% | 89% |
| When new pest management technologies are introduced, it is only a matter of time before pests evolve resistance | 82% | 73% |
| I am concerned about the impact of pesticides on beneficial insects, microorganisms, etc. | 74% | 66% |
| Seed and chemical companies should do a better job of keeping up with evolution of resistance in pests | 66% | 64% |
| Bt-resistant insect pests are not a major concern because new technologies will be developed to manage them | 15% | 13% |
| Herbicide-resistant weeds are not a major concern because new technologies will be developed to manage them | 14% | 9% |
| Management practices | ||
| Poor management by a few farmers leads to premature evolution of resistant pests | 69% | 61% |
| Sometimes I think crop advisers recommend more pesticide use than is necessary | 41% | 41% |
| Pesticide resistance can be managed effectively by individual farmers | 29% | 27% |
| Farmers are less likely to use sound resistance management practices on rented land | 15% | 11% |
| The way farmers use pest management technologies does not really impact the rate at which resistance evolves | 91% | 89% |
Changes in behavior toward HR weed management over time
Table 3 shows a series of statements presented to farmers in the 2013, 2017, and 2022 IFRLP. There has been significant change in the percentage of farmers changing their weed management program due to concern about HR weeds. In 2013, just over half (52%) said that they had done this. By 2017, this was 77%; and, in 2022, 84% reported changing their program. The proportion of farmers making more than one herbicide application rose slightly from 81% in 2013 to 85% in 2022. Interestingly, the number of farmers developing their own herbicide programs declined over the previous decade. Only 36% of farmers said that they did this, compared to 45% in 2013. The proportion of farmers who hire custom applicators to spray herbicides remained stable, declining slightly from 65% in 2013 and 2017 to 63% in 2022.
| 2013 | 2017 | 2022 | |
|---|---|---|---|
| Over the last five years, have you changed your weed management program due to concern about herbicide-resistant weeds?* | 52% | 77% | 84% |
| In the last five years, have you made more than one herbicide application to a single crop in a single season? | 81% | 83% | 85% |
| Do you develop your own herbicide programs? | 45% | 36% | 36% |
| Do you hire a custom applicator to spray herbicides? | 65% | 65% | 63% |
Changes to perceived effectiveness of HR management practices
There are many practices farmers can enact to tackle the threat of HR weeds. In 2013 and 2022, farmers were asked to rate how effective they perceived each practice for this task on a four-point effectiveness scale from not effective at all (1) to very effective (4). Table 4 outlines how the proportion rating each practice effective or very effective changed during this time. Responses were reasonably stable across the decade. However, the perceived effectiveness of cover crop use increased 10 percentage points. Other substantial changes included multiple modes of action in each application and use of crops resistant to non-glyphosate herbicides, which both increased by 8 percentage points. Practices with declines in perceived effectiveness included high planting rates, which dropped 10 percentage points, and tillage, which dropped by 5 percentage points.
| 2013 | 2022 | |
|---|---|---|
| Rotation of crops | 82% | 86% |
| Multiple modes of herbicide action used each season | 77% | 82% |
| Multiple herbicide application timings | 83% | 80% |
| Multiple modes of herbicide action used in each herbicide application | 71% | 78% |
| Tillage | 72% | 67% |
| Inclusion of a forage in the rotation | 57% | 60% |
| Mechanical control (e.g., cultivation) | 55% | 58% |
| Use of crop cultivars that are resistant to herbicides other than glyphosate | 45% | 53% |
| Use of a cover crop | 39% | 49% |
| Higher planting rates | 40% | 30% |
Attitudes toward alternative management approaches
In 2022, farmers were also surveyed on their attitudes towards collaborative initiatives aimed at tackling HR. As shown in table 5, almost half (47%) indicated that a local organization led by farmers would be an acceptable approach to tackling HR weeds. Willingness to participate in a community-wide cooperative group was much lower, with 18% being for this method, and 41% against. However, 41% also suggested that they did not know, indicating a level of apathy or uncertainty regarding community management approaches. Finally, the idea of a government-related mandate was the least favored potential plan to manage HR weeds. Only 6% said that the government should be involved in this way. These results are useful to consider in the future development of policies and initiatives to tackle HR weeds.
| Yes | No | Don’t Know | |
|---|---|---|---|
| Would it be acceptable for a farmer-led local organization to help local farmers to develop plans to manage herbicide-resistant weeds? | 47% | 22% | 31% |
| Would you be willing to participate in a community-wide cooperative weed management group? | 18% | 41% | 41% |
| Should the government require farmers to develop an approved plan to manage herbicide-resistant weeds? | 6% | 78% | 16% |
Conclusion
Overall, survey results suggest that concern for HR weeds among Iowa farmers has grown over the previous decade. This is best demonstrated by the percentage of those changing their weed management programs in the previous five years due to concern for HR weeds growing from 54% in 2013 to 84% in 2022. Iowa farmers are also increasingly apathetic towards the idea that new technologies will be able to manage HR weeds with only 9% agreeing or strongly agreeing with this in 2022 compared to 14% in 2014. To combat the issue of HR, farmers increasingly view practices such as crop rotation and cover crops as being more effective. Going forward, farmers also appear to favor collaboration with local farmer-led organizations compared to working with community cooperatives and the government to tackle HR weeds.
Footnotes
1. This article summarizes results from the 2023 report, Farmers’ Attitudes and Behaviors Related to Weed and Herbicide Resistance Management, available at https://store.extension.iastate.edu/product/16896.
References
Gould, F., Z.S. Brown, and J. Kuzma. 2018. “Wicked Evolution: Can We Address the Sociobiological Dilemma of Pesticide Resistance?” Science 360(6390):728-732. doi: 10.1126/science.aar3780.
Owen, M.D., H.J. Beckie, J.Y. Leeson, J.K. Norsworthy, and L.E. Steckel. 2015. “Integrated Pest Management and Weed Management in the United States and Canada.” Pest Management Science 71: 357-376. doi: 10.1002/ps.3928.
Suggested citation
Hollis, J., K. Dentzman, and J. Arbuckle. 2024. “Iowa Farmers’ Attitudes and Behaviors Related to Weeds and Herbicide Resistance Management: Have they Changed over Time?” Agricultural Policy Review, Spring 2024. Center for Agricultural and Rural Development, Iowa State University. https://agpolicyreview.card.iastate.edu/spring-2024/iowa-farmers-attitudes-and-behaviors-related-to-weeds-and-herbicide-resistance-management-have-they-changed-over-time.