By: Sabina Regmi1, Rebecca Hill1, Dawn Thilmany1, Rebecca Wasserman-Olin1, Adam Osterholzer2 and Punya Nachappa2
1Department of Agricultural and Resource Economics, Colorado State University
2Department of Agricultural Biology, Colorado State University
The wheat stem sawfly (WSS, Cephus cinctus) emerged as a significant threat to winter wheat producers in Colorado in 2010, with the primary concentration of infestations in NE Colorado. Figure 1 shows the average percentage of wheat stem sawfly infestation across Colorado from 2019 to 2024. Infestation was 15% in 2019 and 2020, declined to a low of 7% in 2021, and then increased sharply to 21% in 2022. After a slight decline to 14% in 2023, infestation increased again to 27% in 2024, the highest rate observed in recent history. 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%, significant revenue losses on top of the additional costs for implementing various pest management strategies.

Figure 1: Trends in Wheat Stem Sawfly Infestation in Colorado, 2019–2024.
Note: The data is an average of 100 field sites with 100 wheat stems dissected per site.
Download full report below.

