Photographer: James H. MIller Affiliation: USDA Forest Service Source:www.bugwood.org Copyright: CC BY 3.0
Photographer: Caleb Slemmons Affiliation: University of Wisconsin, Stevens Point Source:www.bugwood.org Copyright: CC BY-NC 3.0
The invasive common reed (Phragmites australis subspecies australis) is a cane-like perennial grass that has rhizomes, forms large stands of clones, and grows from 12 to 16 feet tall. The stems are rigid, hollow and round and are about 1 inch in diameter and are usually 6-13 feet tall. The leafy stems do not branch and shoots and leaves are stiff and sharp because of the high concentration of cellulose and silica content. The leaves are lance-shaped and are 10-20 inches long. The 8-16 inches long seed heads are at the apex, multi-branched and have silky hairs. The leaves are deciduous in the winter. The roots grow about 3 feet deep and the depth of the rhizome system depends on the soil conditions. The rhizomes can be anywhere from 4 inches to 6.5 feet deep but can extend up to 70 feet away from the parent plant. Purple or golden flowers appear at the tips of the tall stem and each spikelet has 3-7 florets each being .5 inch long. Seeds are small and less than .1 inch long.
Even though this plant is worldwide the subspecies australisis thought to be invasive; and considering that no wildlife or herbivores consume this plant gives evidence that it is an invasive. On the East Coast the invasive Phragmites has displaced native Phragmites. The native genotype is still common in the Southwest and Pacific Northwest except along roads and waterways in urban areas. What makes this plant a threat is the common reed changes wildlife habitat, hydrology and increases the fire potential because it has a significantly high biomass. In Connecticut, some rare and threatened bird species are absent from former marshlands because they have become monocultures of the invasive Phragmites. This concept has been seen in other states when there invasive common reed reduces the biodiversity of the waterfowls and plants present.
The common reed produces by rhizomes (vegetatively) or by seeds. The plants can be wind-pollinated, self-fertile or produce seeds by fertilization. Each plant produces thousands of seeds that are dispersed by wind and water. Seed viability is controlled by environmental conditions like day temperature. Also, seedlings will not emerge from depths below 2 inches in the soil. A seed bank in ideal marshy soils may cause a re-infestation after eradication. What also causes the spread of the common reed is the extensive rhizome system. It only takes a small piece of rhizome to sprout up dense stands of clones that are more environmentally tolerate than seedlings. Each rhizome lives for about 2-3 years.
This species was accidentally introduced into the United States in the late 1700s to early 1800s, probably from contaminated ballast water. It was not noticed at first because it is very similar to native Phragmites but it spread west in the 1900s along roads and railroads. Common reed is still sold in nurseries.
Unclear but thought to be from Eurasia
U.S. Habitat: The common reed has broad environmental tolerances; and can grow wherever there is moisture from sea level up to 7,000 feet elevation. It does best in slow or stagnant water with silt bottoms, and it is not tolerant of high salinity or drought.
U.S. Present: All states except Alaska
The species Phragmites australis is considered to be a complex of several subspecies; 11 of the 27 are native to the United States. The native common reed P. australis ssp. americanus can be differentiated from the invasive common reed by a few details. Leaf sheathes on the native common reed are held loose to the stem and become shed in the winter. The glumes and ligules on the native strain are longer than the invasive common reed.
Since the colonies are long-lived any control plan has to be on a long-term basis. Segments of rhizomes are quickly spread by machinery, boat or their trailers, so proper inspection and cleaning of all equipment is necessary. Also, the intentional planting of this plant for erosion control or ornamental reasons should be avoided.
Controlling this plant by physical or chemical means is very difficult and requires years of persistence. Prescribed burning after flowering will reduce biomass and will allow other plants to grow the following spring. Burning should not be performed before flowering because it can stimulate the growth of rhizomes. The most effective method of chemical control is foliar applications of herbicides. It is best applied before the rhizomes develop in late summer or early fall after flowering but again treatments are necessary for several years to kill back re-sprout from rhizomes. Presently, no biological controls for the common reed are available in the United States, but research is being performed on several non-native insects. Because they are non-native, none of the insects have been introduced into the United States; and more research need to be done so it the full impact of the insects are known.
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