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Canada Thistle Rust Fungus Trial

In 2022, the Gunnison Conservation District worked with other Conservation Districts (Shavano and Delta) in our Gunnison-Dolores Watershed, and the Palisade Insectary, to begin a trial for a rust fungus (Puccinia punctiformis) treatment for Canada thistle.  Canada thistle is prevalent in many wet meadows and hay meadows in the Gunnison Basin, and usually requires consistent control efforts with a rotation of herbicides to keep it from taking over an area.  For landowners that are not able to dedicate the time that is necessary, or are hesitant to use herbicides, the host-specific rust fungus may be a future option.  

Rust fungus infections can reduce thistle stem density, and in some cases even eradicate Canada thistle from an area over several years.  The Colorado Department of Agriculture website has a good overview of the rust fungus, it's lifecycle, and some frequently asked questions.

There is still a lot to learn about the rust fungus, including how the site and surrounding vegetation, land management, and environmental conditions impact establishment.  To further understand the rust fungus, the Colorado Department of Agriculture's Palisade Insectary staff will monitor some sites for establishment of the fungus after it's innoculation in fall of 2022, and will have more in-depth monitoring transects on additional sites to measure Canada thistle stem density, mortality, and other variables.  The Gunnison Conservation District has 5 landowners that participated in the trial in 2022, including 4 establishment sites and 9 study transects.  The District is excited to see preliminary results and establishment in summer 2023.  

If you have interest in this program or would like more information, please contact District Conservation Technician Aleshia Rummel (