- Past Infestation and Threat Perception: Sixty percent of farmers reported past wheat stem sawfly infestation, and 86% viewed it as a threat, indicating widespread awareness and concern among Colorado wheat producers.
- Prevention Practices: The most adopted prevention measures were increasing crop diversification (46%) and planting semi-solid or solid-stem wheat varieties (44%), while practices like insecticide use and edge trap cropping were least utilized.
- Regional Differences: Farmers in the Front Range and Northeast areas with higher infestation history reported greater concern and higher adoption of prevention strategies compared to those in the South, where infestation and adoption rates remained low.
Introduction
The wheat stem sawfly (WSS, Cephus cinctus) emerged as a significant threat to winter wheat producers in Colorado in 2010, with the primary infestation concentrated in NE Colorado. There is a considerable interannual variability but an overall upward trend: infestations averaged 15% in 2019–2020, declined to 7% in 2021, rose sharply to 21% in 2022, dropped slightly to 14.3% in 2023, and escalated again to 27.4% in 2024, with evidence of expansion into southern wheat-producing areas (Osterholzer & Nachappa, 2024). These fluctuations may reflect variations in weather conditions, crop management practices, or sawfly population dynamics across years. The total economic impact of yield losses due to WSS average approximately $70 million per year over the 2019–2022 period (Wasserman-Olin et al., 2023). If unmanaged, infestations can result in yield losses between 15% and 40%, alongside additional costs for implementing various management strategies. In 2023, 51 wheat farmers in Colorado were surveyed to study the potential economic impact of wheat stem sawfly in Colorado, as well as to understand adoption patterns of prevention management practices used by the farmers.[1] Of these farms, 29 farmlands were managed within a single county, while 22 were managed across multiple counties[2].
Prevention Measures Used by the Farmers
Table 1 presents summary statistics for WSS prevention strategies reported by farmers across the entire sample. For instance, a mean value of 46% for increasing crop diversification indicates that 46% of surveyed farmers adopted this practice. Among the listed strategies, increasing diversification and planting semi-solid or solid stem wheat varieties were the most used prevention measures. These were followed by practices such as planting larger blocks of wheat and avoiding previously infested areas. The least used measures included insecticide application, reduced tillage, edge trap cropping, and other methods such as undercutting and seed treatment. The table also includes responses to infestation history and perceived threats. Sixty percent of the farmers reported having experienced sawfly infestation in the past, and 86% viewed sawfly as a threat. These findings support the concept that we are likely to note the adoption of multiple prevention strategies in high-pressure areas.
[1] Refer to the working paper “Colorado Farmer Strategies for Addressing Wheat Stem Sawfly Risks: Strategies and Regional Patterns from a 2023 Producer Survey” for additional details on farm counts by county and respondent demographics.
[2] To account for multi-county farms, we evenly divided each farm’s reported total acreage in all crops and wheat acreage across the counties it operated in. For instance, if a farm operated in three counties with a total of A acres, we assigned A/3 acres to each county. After splitting the acreage by county, we removed all non-Colorado farm segments. These included farms based in Nebraska or those that included Chase County.
Note: other measures + includes undercut, tread mulch, Winrow, and seed treatment. 1) N = 50 for survey data (pre-split farms), with 1 farm managed in Nebraska and excluded from this study. Prevention measures statistics were calculated using the original dataset before separating single and multi-county farms because splitting farms would duplicate these adoption measures.
County patterns further support this interpretation. Counties with a high share of farmers reporting past infestation-such as Adams, Logan, Sedgwick, Yuma and Morgan also reported high perceived threat and relatively widespread use of prevention measures like diversification, solid or semi-solid varieties, and planting larger blocks of wheat. In contrast, counties like Kiowa, Cheyenne, and Bent, which reported no past infestation, also reported no adoption of prevention practices and low perceived threat. These differences show that farmers are more likely to use prevention strategies when they’ve dealt with sawfly problems in the past. This highlights the importance of targeted outreach and early warnings in counties with little or no sawfly pressure yet but could be at risk in the future.
Regional analysis
To look at regional comparisons, we identified the CSU Extension region for each farmer based on the county in which they managed their farmland and then grouped the responses into three CSU regions (using designations adopted by CSU Extension): Front Range, Northeast, and South regions. Table 2 summarizes sawfly-related responses by CSU Extension region, highlighting the regional differences in past infestation, perceived threat, and adoption of prevention strategies.
Ninety-one percent of farmers in the Front Range and 82% in the Northeast region reported past sawfly infestation, whereas only 6% of farmers in the South reported the same. Despite the low reported infestation in the South, 71% of farmers there still viewed sawfly as a threat, though this is lower than the 95% reported in both the Front Range and Northeast. Adoption of prevention practices followed similar patterns. Farmers in the Front Range and Northeast reported the highest adoption rates, with over 50% reporting the use of solid or semi-solid stem wheat varieties and increased crop diversification. In contrast, adoption was considerably lower in the South, where few respondents reported using any of the listed strategies. Measures like reduced or no tillage, avoiding previously infested areas, and swathing were more commonly practiced in the Front Range, while edge trap crops remained largely unused across all regions. These findings suggest that while awareness of sawfly as a threat is widespread, actual prevention efforts vary significantly by region likely reflect the differences in previous infestation experiences.
This regional pattern is further illustrated in Figures 1 and supported by the regional statistics in Table 2. Figure 1 shows the proportion of farmers reporting past wheat stem sawfly infestation (left panel) and perceived threat of sawflies (right panel) across Colorado regions. The Front Range and Northeast report high levels of both past infestation and perceived threat, while the South shows lower concern. Consistent with this, farmers in the Front Range and Northeast report greater adoption of prevention practices, particularly diversification and use of solid-stem varieties, compared to limited adoption in the South.[1] These patterns suggest that farmers in higher-pressure regions are more likely to implement multiple prevention strategies and treat the sawfly as a serious concern.
[1] Refer to the working paper “Colorado Farmer Strategies for Addressing Wheat Stem Sawfly Risks: Strategies and Regional Patterns from a 2023 Producer Survey” for or county-level maps of wheat stem sawfly prevention measures by county and regions.
Future Work
As WSS infestation rates continue to rise, it is crucial to understand how farmers have adapted their management strategies compared to two years ago, when pest pressure was lower. Building on the findings from this study, we conducted a follow-up farmer survey in summer 2025 to document changes in prevention practices, perceptions of risk, and adoption of new management strategies in response to increasing infestation levels. Moving forward, we aim to reassess the economic impact of wheat stem sawfly in Colorado, considering the evolving adoption patterns of solid-stem wheat varieties among producers.
Acknowledgement
We would like to thank all the farmers who participated in the summer 2023 survey; this work would not be possible without you! We also thank the Colorado Wheat Research Foundation for funding this work.
References
Irell, B., & Peairs, F. (2023). Wheat Stem Sawfly: A New Pest of Colorado Wheat. Retrieved from Colorado State University Extension: https://extension.colostate.edu/topic-areas/insects/wheat-stem-sawfly-a-new-pest-of-colorado-wheat-5-612/
Osterholzer, A., & Nachappa, P. (2023). Colorado Wheat Stem Sawfly Survey. Retrieved from https://www.csuwheatentomology.com/uploads/1/4/3/6/143627934/sawfly_faq_and_survey_report_2024.pdf
Osterholzer, A., & Nachappa, P. (2024). Wheat Stem Sawfly State-Wide Results. Retrieved from https://coloradowheat.org/wheat-entomology-newsletter-september-18-2024/
Starinieri J., Peirce, E., & Nachappa, P. (2023). Wheat Stem Sawfly Biology and Management. Retrieved from https://agsci.colostate.edu/agbio/wp-content/uploads/sites/127/2023/01/wheatstem-sawfly-factsheet-accessible.pdf
Wasserman-Olin, R., Hill, R., Osterholzer, A., & Nachappa, P. (2023). The economic impact of wheat stem sawfly on Colorado wheat. In Making Better Decisions, 2023 Colorado Winter Wheat Variety Performance Trials (pp. 47–48). Published extension report. https://webdoc.agsci.colostate.edu/csucrops/reports/winterwheat/wheatreport_2024_WFD.pdf