Invasive Species of Concern in Maryland

photo: D. Bean, MDA

ANNAPOLIS, MD (July 16, 2005) - Phragmites australis, also known as common reed, is an exotic invasive grass that is becoming an all too common sight in Maryland. It can grow to heights of 15-20 feet and forms a dense monoculture that can be very difficult to penetrate. The name Phragmites comes from the Greek word “phragma” which means “fence” – a good descriptor of how it can grow! It out-competes native plants by blocking light and occupying all of the growing space underground. Phragmites can negatively impact a marsh it invades by lowering the plant species diversity, providing less desirable habitat for wildlife, and elevating sediment levels so hydrologic flow is changed. This has earned the designation of Invader of the Month for July by the Maryland Invasive Species Council.

This invasive perennial grass quickly spreads by production of underground rhizomes and will continue to send up new shoots throughout the growing season. It is also capable of producing thousands of seeds which are wind dispersed but, fortunately, have low viability. It was likely introduced to North America from Europe in the late 1700’s or early 1800’s via the shipping industry. Once it established near ports along the Atlantic coast, it quickly began spreading into surrounding marshes. Since native Phragmites was already found in many of these marshes, it was not noticed as being an invader. It can grow in just about any habitat, either upland or coastal and is now a common sight along roadsides all over Maryland. Today it is found across the continent and is probably the most aggressive invader of tidal marshes on the Atlantic coast.

In Maryland it begins flowering in July and continues through the growing season. The large fluffy flower heads, or panicles, often start out deep purple or golden in color and then begin to look grey as seeds form and mature. In the fall once cold weather sets in, the leaves will turn golden yellow and drop off but the dead stems will remain standing year round. The high density of standing dead stems even in the summer months are a feature that make marshes invaded by this plant so difficult to walk through. On the other hand, in places such as Maryland where sea level rise is an issue, Phragmites may help preserve coastal marshes by building up the substrate in pace with rising sea levels.

Maryland is very fortunate in having more remnant native Phragmites populations than any other state along the Atlantic coast! Today these native populations are found along creeks and rivers in tidal low salinity marshes. They typically are less dense than the introduced plants, and may have purple color on their stems. They also tend to drop their leaves and die back earlier in the fall. The presence of round black spots on native plants which appear in August and remain on dead stems may also help distinguish native from introduced Phragmites, but the two types appear very similar to most people, and landowners should get expert advice before attempting control.

Introduced Phragmites is very difficult to control due to its substantial below-ground biomass of roots and rhizomes. The spread of small stands can be controlled by regular mowing, particularly before seeds are produced, but mowing will not kill the plant. Most control programs spray with herbicide but monitoring and multiple applications over several years are usually needed to effectively kill it. Going after newly established stands before they have completely taken over a marsh is probably the most effective means of controlling this plant.

For more information about mute swans and other Invasive Species of Concern, visit www.mdinvasivesp.org

photos available electronically on request.