Phragmites is one of Toronto’s most invasive plants, known for its ability to dominate wet areas, outcompete native plants, and disrupt local ecosystems. The shoreline of Grenadier Pond, once abundant with common cattail and the regionally rare sweet flag, has been heavily impacted by dense stands of Phragmites. Effective management is essential to restoring the pond's ecological balance.
Timing: The first round of treatment took place in September 2024. Additional treatment is planned for fall 2025.
Location: Grenadier Pond, High Park, Toronto
Image: Map showing locations of both aquatic and terrestrial populations of Phragmites that are currently being managed.
Method:
Due to the establishment of these extensive Phragmites stands within and around the pond’s shoreline, a combination of chemical and non-chemical methods will be used. RoundUp WeatherPro (glyphosate) will be applied to terrestrial Phragmites (on land), while Habitat Aqua (imazapyr) will target aquatic populations (in water). Non-chemical methods, including the use of an amphibious cutting machine (Truxor) and manual techniques like spading and cut-to-drown, will be employed to manage Phragmites. Since June 2024, volunteers from the High Park Volunteer Stewardship Program have been regularly spading in the southern portion of the pond, where the infestation is in its early stages and mixed with native plant species.
Environmental Precautions:
The project follows an Integrated Pest Management approach, which uses Best Management Practices to minimize environmental impacts. Pesticide application is timed to minimize risks to wildlife, with treatment occurring after most turtle hatchlings have emerged, outside of breeding windows of most wildlife and when native plants are beginning to enter dormancy. Phragmites, still actively growing in the fall, will absorb the pesticide into its roots, effectively killing the plant.
Public Health Guidance:
The City’s Invasive Management Program has been reviewed by Toronto Public Health and complies with all provincial and federal pesticide regulations, including Health Canada's Pest Management and Regulatory Agency (PMRA) guidelines. Where the pesticides are being used, the public is advised to avoid treated areas while warning signs are posted. Signs will be placed 24 hours before treatment and removed 48 hours afterward.
Management Goals and Expectations
The goal is to significantly reduce the Phragmites population size in Grenadier Pond over the next 2 years. Pesticide treatment took place in September 2024 and follow-up treatment is expected to occur in September 2025. Following the 2024 treatment, dead standing stems were cut and piled on site in February 2025. This will allow for ease of treatment the following year, and where necessary dead standing material can be left to maintain cover for wildlife.
Over time, as the Phragmites population is reduced, it is anticipated that the native seed bank will rebound, and we will see the re-establishment of native species. Ongoing Phragmites management will be required to ensure that the plant does not re-invade. City staff, the TRCA and volunteers will carry-out ongoing management activities including monitoring and mechanical control methods. Once Phragmites populations have been significantly reduced, careful monitoring will take place to determine where native plantings are necessary to restore the shoreline areas.
For more information about what the City is doing to manage phragmites across Toronto, visit: Phragmites Maintenance