You would have seen these along roadsides, especially near ditches. Tall grasses that sway in the wind. This is likely phragmites, also known as common reed (Phragmites australis L.). It is a very widespread weed, in fact one of the world’s most common plant species, being able to grow in wetlands from the tropics to the far north. As a result of its global distribution, various races and types have evolved. In North America, there is a native type of phragmites that has achieved balance with its environment. However, races from Europe have been introduced over the years and since they have different biological features, they have become invasive. This means they will grow unrestricted and can rapidly establish monocultures that exclude native vegetation and have negative effects on wildlife.
Traditionally, management of phragmites involves cutting of stems or even burning, but these have moderate success. These interventions would set back stands, forcing them to regrow. The problem is that phragmites is a perennial with an extensive rhizome network. These very thick underground stems allow storage of food reserves and also cause patches to regrow easily. For cutting or burning to be successful, they would have to be repeated multiple times during a season in order to exhaust the plant’s reserves.
As far as herbicides are concerned, only three active ingredients have phragmites on their label and can legally be used. Glyphosate, the active ingredient in Roundup WeatherMax and other products, is systemic, non-selective and non residual. The label states application on phragmites must be done at rates between 2.0 to 8.0 L/Ha (0.8 to 3.2 L/ac). Imazapyr is another systemic, non-selective herbicide which has soil residual activity. It is generally used for general weed control on non-crop sites. Imazapyr is sold as Arsenal Powerline (for terrestrial applications) and Habitat Aqua (for aquatic applications). The third active ingredient is sodium chloride (table salt) in the herbicide RagWeed Off. Sodium chloride acts as a contact herbicide and the label states two to four applications per year over multiple years should be done in order to attain desirable phragmites stand reduction. While glyphosate and imazapyr are interesting products due to their systemic action it would be favourable to have other, more selective options, that would permit a more rapid re-establishment of native plants.
Herbicide field trials in 2019 and 2020