THE HISTORY
Invasive phragmites is a tall wetland grass found in 32 states across the U.S. It invades wetlands, marshes, estuaries, and bays, and has spread to major rivers and streams. Accidentally introduced to North America in the late 17th and early 18th centuries, phragmites has adapted well to wetland environments, thriving in moist soils or covered with shallow water for part of the year. It also infests smaller wetlands and disturbed urban areas such as drainage ponds, borrow pits, riparian corridors, and irrigation ditches.
While several native phragmite species exist in North America, they were non-aggressive and coexisted with other plants. However, invasive phragmites are highly aggressive, outcompeting native species and forming dense monocultures. As a result, native phragmites have become rare.
The spread of invasive phragmites harms the environment by reducing wildlife habitats, decreasing plant diversity, and altering water levels by trapping sediments. It also poses additional risks, such as being a fire hazard and obstructing roadside visibility, which can lead to accidents. Phragmites can reduce property values by blocking lake views and restricting access to swimming, fishing, and hunting areas. Unlike many native wetland plants, phragmites is not a valuable food source for waterfowl.
Invasive phragmites plants can grow up to 15 feet tall and primarily spread through below-ground rhizomes and above-ground stolons. Although the plant produces seeds, they rarely germinate into new plants. Rhizomes grow actively from late summer through early winter, forming a dense underground mat. These rhizomes can grow up to six feet per year and eventually extend over 60 feet in length in an established stand. They can also penetrate more than six feet deep into the soil. Activities like dredging and disking in wetlands can inadvertently promote the spread of phragmites.
PRODUCTS
The most effective method for controlling phragmites is treatment with herbicides, which ensures that the plant’s underground parts are thoroughly killed. Since phragmites typically grows in or near water, herbicides with aquatic registration are necessary. Arsenal AC and Roundup Custom are the most effective products for controlling them. Both are non-selective herbicides that kill most plants they contact. The key difference is that Roundup Custom is active only on foliage, while Arsenal AC works on both foliage and soil.
MANAGEMENT
The ideal time to spray phragmites is from July through October. For large infestations, aerial application is most effective, while smaller patches are typically treated with high-volume ground or boat equipment. Very small patches can be managed using backpack sprayers. Studies have shown that repeated mowing of invasive phragmites without accompanying herbicide treatment is ineffective and may increase the density of the plants.
Manipulating water levels can also aid in controlling phragmites. Lowering the water level to expose the soil allows herbicides like Arsenal AC, which has soil activity, to better target the rhizomes. Flooding the area a month after herbicide application can further stress the phragmites by creating a low-oxygen environment. This flooding should be at least 3 feet deep and last for a minimum of 30 days. The phragmites must be submerged by at least one foot of water, as shallow flooding could enable the plants to send up “snorkelers,” or shoots that provide oxygen and help the plants survive.
To achieve optimal control, each herbicide should be used according to its specific characteristics. Since Roundup Custom lacks soil activity, it is best applied to phragmites colonies adjacent to or on shorelines where desirable trees and shrubs are present. Be careful to keep the spray off the leaves of these desirable species to avoid damage. Arsenal AC is more effective for large colonies, but should be kept at least 50 feet from the shoreline to prevent uptake by root systems in the area. For maximum control, spray the perimeter of the colony with Roundup Custom.
Azelis A&ES has experienced representatives that can help you make the right decision for your land management objectives. We are ready to provide you with a safe and effective solution.