May 19, 2025
Adam Osterholzer: adam.osterholzer@colostate.edu, 970-222-9568
Dr. Punya Nachappa: Punya.Nachappa@colostate.edu, 785-383-4873
Visit our website at: https://www.csuwheatentomology.com/.
Wheat Stem Sawfly (WSS) Updates
Wheat stem sawflies have started to emerge, and we captured several individuals in New Raymer on May 8th (photo below). Typically, males emerge first, followed by females. Males emerge earlier, allowing them to mate with virgin females, increasing their reproductive fitness.
Our degree-day model predicts the following for Weld and nearby counties:
- May 3rd (154DD) for 5% emergence
- May 20th (223DD) for the peak
The cool and wet weather early this week may delay their emergence, but we predict that sawflies will become more abundant later in the week.
Where to Scout:
Wheat fields are particularly vulnerable along edges adjacent to stubble from the previous year. This is because adult wheat stem sawflies emerge from the stubble and move into the current season’s crop. In the area shown below, scouting efforts should be concentrated along the path indicated by the red arrow, where sawfly density is expected to be highest. A sweep net or bug net is used to capture adult sawflies during scouting.
When to Look for Adult Sawflies
Adult sawfly emergence is influenced by weather conditions. Rainfall, strong winds, and cold temperatures can delay or suppress their activity. Therefore, scouting should be prioritized on warm, calm mornings when adults are most likely to be active. Scouting during poor weather may give the false impression that sawflies are absent.
Project Highlight: Wheat Genetics Research Center (Kansas State University) screening wild wheat species for novel sources of resistance
This ongoing project is conducted in collaboration with the Wheat Genetics Research Center at Kansas State University and is funded by CWAC. Wheat lines are grown in cone-tainers in our greenhouse and then exposed to natural wheat stem sawfly infestation in the field. Since sawflies cannot be reared in a laboratory setting, we must transport the plants to infested field sites. This year, we plan to conduct infestations in Akron and Byers due to a significant decline in sawfly populations in the New Raymer and Orchard areas.
Wheat Diseases
For wheat disease updates by Dr. Robyn Roberts, please see:
https://coloradowheat.org/category/news-events/wheat-pest-and-disease-update/
Acknowledgements
We would like to acknowledge the tireless work of CSU researchers and extension agents for reporting pest problems throughout the state.
May 2, 2025
Adam Osterholzer: adam.osterholzer@colostate.edu, 970-222-9568
Dr. Punya Nachappa: Punya.Nachappa@colostate.edu, 785-383-4873
Visit our website at: https://www.csuwheatentomology.com/.
Wheat Stem Sawfly Updates
Every year, we visit wheat fields at Orchard and New Raymer, our historically high sawfly sites, to monitor wheat stem sawfly emergence. In both locations, the sawflies are still in the pupal stage (Figure 1). They are developing adult features, such as legs, eyes, etc. Given this, we expect adult sawfly emergence next week.
Our degree-day model predicts the following for Weld and nearby counties:
- May 3rd (154DD) for 5% emergence
- May 20th (223.3DD) for the peak
- June 1st (287.7DD) for 95% decline
In areas with suspected sawfly populations, growers should monitor the edges of their fields for adults. The insects prefer to fly on calm, warm days. Planting semi-solid wheat varieties can help mitigate losses in areas of high infestation.
Project Highlight: Beneficial Bug Baler
CSU and the University of Nebraska-Lincoln are undertaking a new project this year with funding from Colorado Wheat Research Foundation (CWRF). We are collaborating with scientists from USDA-ARS to obtain and distribute bales from Nebraska that possess high populations of parasitoid wasps, which are natural enemies of the sawflies. Bales were unfurled at 8 locations in CO-3 in New Raymer, 3 in Orchard and 2 in Byers (Figure 2). We will monitor parasitoid emergence and impacts on the sawfly infestation. This initiative was only possible with the support of our grower cooperators, who have kindly let us use the fields for the experiments!
New Region of Concern: South of I-70 Corridor
Our lab conducts an annual statewide survey for sawfly infestation (Figure 3). In 2024, we saw substantial infestation in fields south of Burlington. Growers in this region are advised to scout for sawflies throughout the season. We will continue to monitor the spread and provide updated information. Results will be provided to Colorado wheat and will also be posted at
https://www.csuwheatentomology.com/.
Wheat Diseases
For wheat disease updates by Dr. Robyn Roberts, please see: https://coloradowheat.org/category/news-events/wheat-pest-and-disease-update/
Acknowledgements
We would like to acknowledge the tireless work of CSU researchers and extension agents for reporting pest problems throughout the state.