From the shoreline of Toronto’s waterfront to its interior parklands, an invasive species is outcompeting native plants, taking over the city’s waterways, reducing wildlife habitat, and restricting the movement of wetland animals.
Phragmites, known as Phragmites australis or Common Reed, is an aggressive, non-native perennial plant from Eurasia that grows on land and in water. It has become one of the city’s most notorious invasive species, and is also a major threat to Canada’s biodiversity, wetlands, and beaches.
The plant is considered invasive because of its ability to spread rapidly over large areas, dominate wetland habitats, form into dense monoculture stands, lower water levels, disrupt nutrient cycles, create fire risks, and release toxins from its roots that hinder the growth of neighbouring plants.
“It’s probably most prevalent in southern Ontario because that’s thought to be one of the main areas where it colonized first when it arrived from Europe. But in 2005, it was named Canada’s worst invasive plants. So, Ontario is definitely not the only province to suffer from this plant,” Karen McDonald, senior manager, ecosystem management, at Toronto and Region Conservation Authority (TRCA), told Now Toronto on Monday.
According to McDonald, Phragmites also impact human habitats by reducing visibility on roads, creating flooding hazards, damaging infrastructure, and lowering visual standards closely related to property values.
“If you’re at a four-way stop or you know, a two-way stop and you need to make a corner, but the Phragmites is blocking your view, and you can’t see that car coming… This plant will also damage infrastructure, it can grow through asphalt, and then it also, because of the crazy height that it grows at, it can also block views resulting in aesthetic degradation,” McDonald told Now Toronto.
PHRAGMITES: TALL, FEATHERY, FLOURISHING IN THE SUMMER
Phragmites is often identified by its tall, blue-green stalks and flat, alternating leaves, with a distinctive hairy fringe at the base of each leaf. In the late summer and fall months, the plant produces dense, cascading flower heads that start purple and turn fluffy and tan as they mature.
“Its primary vegetative growth is in the summertime in June and July. It flowers in August and September, so that’s when it develops this really lovely dark brown flowerhead, and then through the fall months from September through to the end of October, it starts to get yellow as it translocates its nutrients,” McDonald added.
“So, that means that it’s basically taking nutrients from the stem and the leaves to store and its underground rhizomes so that it’s got a lot of energy when the snow melts to grow in the spring.”
As a perennial grass, Phragmites can grow back each year, often exceeding five meters. This makes it difficult to fully remove, as it can produce up to 2,000 seeds annually, which spread over large areas. Additionally, these seeds can be unintentionally transported on clothing, tire treads, and other moving objects.
McDonald notes that it is important for people to know that Phragmites, while visually appealing for things like decorative arrangements, is restricted in Ontario, adding that invasive species such as these are the biggest global threat to biodiversity after direct habitat loss.
“It’s illegal to buy, sell or trade it [Phragmites]. I saw someone last week by the side of the road cutting down Phragmites, and I’m sure they were going to put in their fall planter, and I would encourage everyone to please not do that.”
TREATING AND MANAGING PHRAGMITES INFESTATIONS
To address the impact of the invasive plant on wetland habitats, the City of Toronto has adopted an Integrated Pest Management (IPM) approach, combining both chemical and non-chemical methods to manage, remove, and reduce Phragmites.
Non-chemical treatments include “spading,” which involves using a shovel to cut the plant’s stalks below the soil surface, limiting the Phragmites ability to photosynthesize. While this manual technique has proven effective in the Community Stewardship Program across several Toronto sites, it requires repeated treatments throughout the growing season.
Another non-chemical “cut-to-drown” method is used to cut Phragmites’ stalks below the water’s surface. This technique deprives the plant of oxygen and light, weakening it over time. For this procedure to be effective, the water depth must be at least 15 cm deep.
For larger, more established populations of Phragmites, the city also uses herbicides, such as RoundUp WeatherPro (containing glyphosate) and Habitat Aqua (containing imazapyr), as chemical treatments.
According to the city website, research into biological control methods for managing Phragmites long-term is ongoing, including the study of two moth species that could potentially reduce the plant’s competitive advantage. The city adds that it is collaborating with researchers on trial releases of these insects in specific parks.
The TRCA has also taken steps to successfully reduce, manage, and remove invasive Phragmites from wetland habitats. This includes mapping geological features, plant density, and access and elevation to better understand the infestation and plan appropriate treatments.
“We need to understand if there’s standing water because that changes some of the techniques that we can use to manage it. We also need to understand some of the site constraints, like access or different changes in terrain or elevation and all of these things are implicated in what management’s technique is selected, McDonald said.
Generally, managing a site requires a minimum of three years, unless the infestation is in its early stages. McDonald notes that once funding is secured for this timeframe, successful management can be achieved.
“Ideally, you’re going to have an even longer follow up strategy because of the perseverance of this plant in our landscape is likely to reinfest the site again… lots of people think that you can just sort of, you know, treat it with herbicide once and walk away, but not with an invasive plant. You have to keep coming back to make sure that your technique actually works the first time, and it’s probably going to need to follow up.”
GETTING INVOLVED
Each year, the TRCA organizes one to two events focused on combatting invasive species, inviting the community to take part in wetland conservation efforts. The “Look After Where You Live” initiative encourages organizations to involve their staff in reducing the invasive species.
To learn more about the Phragmites management efforts through the TRCA or to get involved, click here.
