Phragmites australis

What is Phragmites?

Phragmites australis, also known as Common Reed, is a non-native perennial grass that invades wet or moist areas, growing both on land (terrestrial) and in water (aquatic). This tall grass can reach up to 5 meters in height, forming dense stands that outcompete native vegetation, reduce biodiversity, and alter wetland ecosystems.

Why is it a problem?

Phragmites has rapidly spread throughout Ontario in recent decades, forming monocultures (where nothing grows except for Phragmites) that:

  • Dominate disturbed habitats.
  • Release toxins from their roots, inhibiting the growth of neighbouring plants.
  • Lower water levels and alter nutrient cycles in wetlands.
  • Grow in dense stands creating barriers that reduce habitat and restrict the movement of wetland wildlife.

How can you Identify Phragmites?

Phragmites can be identified by its:

  • Tall, blue-green stalks with flat, alternate leaves.
  • Hairy ligule at the base of the leaf blade, distinguishing it from other grasses.
  • Dense, cascading flower heads that change from purple to whitish-tan and become fluffy in the fall.

A dense stand of Phragmites australis growing in water

How is the City managing it?

The City is taking an Integrated Pest Management (IPM) approach that combines proven strategies to manage invasive species using both chemical and non-chemical methods. The City of Toronto employs a variety of these researched and effective techniques, to address the challenges posed by Phragmites. 

Mechanical Removal:

Mechanical removal weakens Phragmites by cutting the stalks, reducing the plant’s ability to photosynthesize and depleting its energy reserves over time. This method is labor-intensive and may require multiple treatments to be effective. The two main mechanical techniques used by the City are:

  • Spading:
    Spading involves using a shovel to cut Phragmites stalks below the soil surface, limiting photosynthesis. This labour-intensive manual technique has been successfully used by Community Stewardship Program volunteers in several sites across Toronto. It requires repeated treatments throughout the growing season.
  • Cut-to-Drown:
    This technique is used in aquatic environments, where Phragmites stalks are cut below the water's surface to deprive the plant of oxygen and light, ultimately weakening it. Water must be at least 15 cm deep for this method to be effective. To enhance efficiency, machines like the Truxor amphibious cutting tool may be used.

Chemical Treatment:

For large, established Phragmites populations, herbicides may be the most effective management option. Any herbicide used is applied by licensed professionals who strictly adhere to all provincial and federal regulations. The herbicides used have undergone rigorous safety testing and are applied at concentrations that are effective against the target species while minimizing impact on non-target plants, animals, and aquatic life.

The City of Toronto also follows best practices for herbicide application, ensuring that treatments are conducted in a manner that minimizes risks to public health and the environment. This includes careful planning of treatment times to consider seasonal wildlife activities, monitoring weather conditions such as rain or wind to prevent drift, and placing clear signage to inform the public about areas being treated.

  • RoundUp WeatherPro (active ingredient glyphosate):
    RoundUp WeatherPro is approved for the treatment of Phragmites on land but not approved for over-water use in Canada. The chemical glyphosate inhibits a key process plants, preventing it from making essential proteins, which weakens and eventually kills the plant. This process is not found in animals or humans, which is why is it generally considered to have low toxicity to non-plant organisms.
  • Habitat Aqua (active ingredient imazapyr):
    Habitat Aqua is approved for the treatment of Phragmites growing in water. The chemical imazapyr works by blocking a process necessary for protein production, leading to the plant's death. This process is not found in animals or humans, which is why is it generally considered to have low toxicity to non-plant organisms.

Biological Control:

The University of Toronto is researching biological control methods to manage Phragmites long-term. Two moth species are being studied for their potential to reduce Phragmites' competitive advantage by feeding on the plant. The City is collaborating with researchers on trial releases in specific parks.

For more information on Phragmites and best management practices:
Phragmites - Ontario Invasive Plant Council