Giant reed
(Arundo donax)
A giant reed is a tall, robust perennial grass that often grows in moist soil. Its stems resemble cane and can grow very densely excluding other vegetation and altering wetland habitats.
Other names for this plant include:
- Common names: Giant cane, Spanish cane, Colorado river reed, wild cane, Carrizo and Arundo
Classification in Wisconsin: Prohibited
- Ecological Threat
-
- Invades moist habitats including lakeshores, riverbanks, wetlands and roadways. It is common in disturbed areas and can tolerate brackish waters, drought, and alkaline to acidic conditions.
- Thick rhizomes can spread quickly and impact flood control measures. Giant reed alters hydrology, diversity of species, and wildlife habitat and increases the risk of fire.
- The primary means of spread is root fragmentation.
- Identification
-
Leaves: Blue-green colored, sharp-edged leaves grow up to 2 inches wide and over a foot long. The leaves wrap around the stem to form a sheath and at this junction, a thin membranous ligule can be seen.
Flowers: A long dense plume appears in late summer at the top of the plant, purplish, aging to silver, and up to 36 inches in length.
Fruits & seeds: Seeds are not viable outside their home range; the plant reproduces by stem fragment or rhizome.
Roots: Tough, thick, knobby rhizomes spread extensively in good conditions, forming thick clonal mats that can extend over several acres and are up to 3 feet wide.
Stems: Very robust and bamboo-like, they can grow up to 25 feet in height and 1.5 cm in thickness. The hollow stems grow very densely, making access through an area difficult.
Similar species: Most often seen as a larger version of common reed (Phragmites australis). The plant's height and leaf size are much more significant than common reeds. Common reed has only hairy ligules, while a giant reed's ligule is a papery membrane with short hairs on the edge. It might also be confused with certain bamboo species.
- Distribution
-
Currently, there are no reports of giant reeds in Wisconsin. Have you seen it? Please send us a report.
- Control
-
Mechanical: Not recommended apart from very young, newly established plants due to large and deep rhizomes. Pulling or digging newly establishing plants in moist or loose soil may work.
Chemical: Translocating herbicides is one of the few effective ways of controlling giant reed infestations. Foliar spraying in late summer/autumn is common, sometimes involving cutting and allowing the plant to regrow before spraying. Applying herbicides immediately to cut stems can also be an effective control method.
Biological: Research is being done in areas of the southwestern United States on biocontrol agents including a wasp, scale insects and flies.
- Resources
- Sources for content:
- USDA Forest Service "Weed of the Week" factsheet [exit DNR].
- Invasive Species Specialist Groups: Global Invasive Species Database
