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Giant reed

(Arundo donax)

Photo of giant reed
Photo credit: Leslie J. Mehrhoff, University of Connecticut, Bugwood.org

Giant reed is a very tall and robust perennial grass that often grows in moist soils. Its stems resemble cane and can grow very densely excluding other vegetation and altering wetland habitats.

Overview

Other names for this plant include:
  • Common names: Giant cane, Spanish cane, Colorado river reed, wild cane, Carrizo and Arundo
Ecological threat:
  • Invades moist habitats including lakeshores, riverbanks, wetlands and roadways. It is common in disturbed areas and can tolerate brackish waters, drought conditions and alkaline to acidic conditions.
  • Thick rhizomes can spread quickly and impact flood control measures. Giant reed alters hydrology, diversity of species, wildlife habitat and increases the risk of fire.
  • The main means of spread is root fragmentation.
 Overview map of prohibited classification in WI
Prohibited (red) counties

Classification in Wisconsin: Prohibited

Species Assessment Groups (SAG) were assembled to recommend a legal classification for each species considered for NR 40. The recommendation for Giant Reed was based upon this literature review [PDF] developed by the department.

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 its 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 thick.

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 height of the plant and size of the leaves are much greater than common reed. Common reed has only hairy ligules, while 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 reed in Wisconsin. Have you seen it? Send us a report.

Control

Mechanical: Not recommended apart from very young, newly established plants due to very large and deep rhizomes. Pulling or digging newly establishing plants in moist or loose soil may work.

Chemical: Translocating herbicides are considered 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 prior to spraying. The application of herbicides immediately to cut stems can also be an effective method of control.

Biological: Research is being done in areas of the southwestern United States on biocontrol agents including a wasp, scale insect and fly.

Photos

View giant reed pictures in our photo gallery!

Resources

Sources for content:
  • USDA Forest Service “Weed of the Week” factsheet [exit DNR].
  • Invasive Species Specialist Groups: Global Invasive Species Database
Links for more information: