Giant Reed (Arundo donax)

plants, terrestrial, tier 2

History & Introduction

Arundo donax is a very tall, perennial grass that forms dense stands on disturbed sites, sand dunes, riparian areas and wetlands. Arundo is native to eastern Asia and known to be cultivated through Asia, southern Europe, northern Africa, and the Middle East for thousands of years. In North America, it was intentionally introduced from the Mediterranean to the Los Angeles area in California in the early 1800s and has been widely planted throughout the warmer states as an ornamental and for erosion control along drainage canals. It has escaped cultivation as far north as Virginia and Missouri, and abundant wild populations occur along the Rio Grande River. In LIISMA, there are three known populations of Arundo within Nassau and Kings counties. Arundo donax is a tier 2 species listed for eradication in New York.

Identification & Biology

Arundo typically grows up to 20 feet, but in ideal conditions, can exceed 30 feet in height. It is among the largest of the grasses and the largest of the genus. It produces tall, hollow cane-like stems up to an inch in diameter and grey-green swordlike leaves that are alternate, 12-24 inches long and up to 2.5 inches wide, with a tapered tip and a hairy, “S” shaped cuff at the leaf base. Overall, the plant resembles a much taller version of the Phragmites australis (common reed) or a member of the bamboo family.

Arundo flowers in late summer, bearing upright, feathery plumes 16 to 24 inches long with seeds that are rarely fertile. Instead, it mostly reproduces vegetatively by tough, fibrous underground rhizomes that form knotty, spreading mats which penetrate deep into the soil. Stem and rhizome pieces less than 2 inches long and containing a single node could sprout readily under a variety of conditions.

Arundo is adapted to a wide variety of ecological conditions, but is generally associated with riparian and wetland systems. It is distributed across the southern United States from Maryland to California. Plants can grow in a variety of soils, from heavy clays to loose sands and gravelly soils, but prefer wet drained soils, where they produce dense monotypic stands.

Damage and Concern

Arundo is a highly invasive plant in southwestern North America and its promotion as a biofuel in other regions is of great concern to environmental scientists and land managers. Through invasive spread and subsequent plantings as an ornamental plant, and for use as reed in woodwind instruments, it has become dominant in North American freshwaters, and its range continues to expand across the continent.

Arundo is an exceptionally fast growing plant, growing about 4 inches per day and reaching a mature height of 25 feet in about 12 months. The plant is very tolerant of a variety of environmental conditions and can be found growing in damp riparian areas, and it is tolerant of moderately saline soils too. Because stands of Arundo are so dense, native plants are typically displaced and the animals associated with these native plants are unable to utilize the plant, so their populations decline also. To present knowledge, Arundo does not provide any food sources or nesting habitats for wildlife. Replacement of native plant communities by Arundo results in low-quality habitat and altered ecosystem functioning. For example, in California, Arundo infestations are particularly problematic because the plant chokes out native willows. It can also provide a lot of fuel for fires which are typically very uncommon in riparian areas. Arundo appears to be highly adapted to fires and highly flammable throughout the drier months of the year. After fires, rhizomes can spread quickly, outgrowing native plants and colonizing riparian corridors.

Other damage and concern caused by Arundo includes stems and leaves that contain a variety of harmful chemicals, including silica and various alkaloids, which protect it from most insects and deter wildlife from feeding on it. In addition, a waterside plant community dominated by Arundo may also have reduced canopy shading of the in-stream habitat, which may result in increased water temperatures. This may lead to decreased oxygen concentrations and lower diversity of aquatic animals.

Management & Control

Manual Control

Hand removal is very difficult, but digging can be used to target individual plants (usually less than 6 feet tall). To improve handling, first cut the canopy near the surface by using a chainsaw, machete, or pruning shears before pulling up the remaining portions of stems, rhizomes, and roots. Shovels, mattocks, or pick-axes are the most commonly used tools. The root mass and associated rhizomes must be entirely removed from the soil. Uprooted material should be removed or burned onsite to prevent rerooting.

Mechanical Control

Mechanical methods used to remove Arundo range in scale from individual plant treatment (digging out with a hand tool, backhoe, excavator, etc.) to broad scale clearing with hammer-flail mowers, root plows, rakes, etc. Mechanical control of areas with Arundo donax is usually more effective when used in combination with chemical control and the planting and/or seeding of desired native species as followup. Large-scale mechanical control usually causes major soil disturbance and interferes with native plant establishment.

Chemical Control

Application of herbicides on Arundo are most effective after flowering and before dormancy. During this period, usually mid-August to early November, the plants are actively translocating nutrients to the root mass in preparation for winter dormancy. This may result in effective translocation of herbicide to the roots. An investigation to test the effectiveness of glyphosate for control of giant reed was conducted in southern California by Caltrans, the state transportation agency. Results indicate cut-stem treatments, regardless of time of application (May, July, or September), provided 100% control with no resprouting. In contrast, virtually all plants that were left untreated following cutting resprouted vigorously. Foliar treatments produced highly variable results with top die-back varying from 10 to 90% and resprouting ranging from 0 to 100% at various sites. Remember to follow all directions on the pesticide label before application or to consult with a professional pesticide applicator.

Monitoring & Reporting

LIISMA is currently monitoring Arundo donax as part of our Early Detection and Rapid Response program. As reports of the species are collected, LIISMA is dedicated to delineating and managing any early emerging infestations of the species before they become widespread. Arundo is currently a Tier 2 species on Long Island, prioritized for early detection and containment.

Your reports matter to us– report the species to iMapinvasives as soon as you detect it.