Giant Reed | Arundo donax

Giant Reed
California Pest Rating for
Giant Reed | Arundo donax
Family: Poaceae
Pest Rating: B  | Proposed Seed Rating: R

Initiating Event:

There have been queries about growing tracts of giant reed in CA for use in biofuel production.

History & Status:

Background: Arundo donax is a tall, erect, perennial cane or bamboo-like grass, 2 to 8 meters high. It is one of the largest of the herbaceous grasses. The fleshy, almost bulbous, creeping root stocks form compact masses from which arise tough, fibrous roots that penetrate deeply into the soil. The culms reach a diameter of 1 to 4 cm and commonly branch during the second year of growth. These culms are hollow, with walls 2 to 7 mm thick and divided by partitions at the nodes. The nodes vary in length from 12 to 30 cm. The leaves are conspicuously two-ranked, 5 to 8 cm broad at the base and tapering to a fine point. The bases of the leaves are cordate and more or less hairy-tufted, persisting long after the blades have fallen. There can be variability in leaf and cane dimensions within a stand, possibly in response to water availability. Arundo donax was widely planted in the 19th century in CA for its bamboo-like stems. It’s planting was actively promoted in the 1950s by the USDA for use in erosion control along stream banks.

Arundo donax has been nominated as one of the top 100 Worst Invaders of the World by the Invasive Species Specialist Group of the World Conservation Union ( It was first introduced to the United States by Spanish colonists in the 1700’s and introduced again to California in the early 1800’s for erosion control in drainage canals. It is now a major invasive threat to riparian areas in California, as well as other southwestern states and it is listed as one of the twenty most invasive weeds in California and as a noxious weed in Texas.

Large infestations of Arundo donax are difficult to eradicate given that all

rhizomes must be removed or killed to prevent re-sprouting. This can cost from $7000-$25000 per acre, depending on difficulty of access. Typically a combination of mechanical removal and application of a systemic herbicide (e.g., glyphosate) provide the best control. Care must be taken to ensure that removed plant material does not sprout. Research on the biological control of Arundo donax in the United States has led to the recent release of a wasp, Tetramesa romana Walker (Hymenoptera: Eurytomidae), but its effects on population levels of Arundo donax are currently unknown .

 Worldwide Distribution: Arundo donax is native to many tropical to warm temperate regions from northern Africa and the Middle East eastwards through eastern and southeastern Asia (CABI, 2011a). It has been introduced into similar climates around the world in southern Europe, Central America, South America, and the Caribbean. It is invasive in southern Africa, the western United States, southern Europe, and the Azores (Weber, 2003).

California Distribution: Arundo donax is found along waterways throughout much of CA as far north as southern Humboldt County. It is missing from Northeastern CA, the high mountains, and it is rare in the desert region (Consortium of California Herbaria).

California Interceptions: Arundo donax is occasionbally sold in nurseries in CA and has been detected during nursery surveys.

This risk Arundo donax would pose to California is evaluated below.

Consequences of Introduction:

1) Climate/Host Interaction: The risk of Arundo donax is High (3) as illustrated by the broad distribution of the pest in California and its spread over the last 100 years.

-Low (1) not likely to establish in California or likely to establish in very limited areas.

-Medium (2) may be able to establish in a larger but limited part of California.

-High (3) likely to establish a widespread distribution in California.

2) Host range.  Arundo donax does not require any one host, but grows wherever ecological conditions are favorable. It receives a High (3) in this category.

Evaluate if the pest would have suitable hosts and climate to establish in California:

Evaluate the host range of the pest:

-Low (1) has a very limited host range

-Medium (2) has a moderate host range

High (3) has a wide host range

3) Pest Dispersal Potential: Arundo donax is a plant that spreads via water flow and human dispersal from rhizomes or stem fragments. It does not reproduce from seed in North America. The Risk is Medium (2).

Evaluate the dispersal potential of the pest:

-Low (1) does not have high reproductive or dispersal potential

Medium (2) has either high reproductive or dispersal potential

-High (3) has both high reproduction and dispersal potential

4) Economic Impact: Risk is Medium (2) as Arundo donax only occasionally invades agricultural land. It can lower yields in some ranching systems, where Arundo donax blocks access to water. Although Arundo donax was once recommended for stream bank stabilization, its shallow roots mean that bank undercutting is frequent in Arundo donax infestations. Bridge and levee damage or failure have been partially ascribed to dense Arundo donax stands, due to flow conveyance loss.

Evaluate the economic impact of the pest to California using these criteria: Economic Impact: B, G 

A. The pest could lower crop yield.

B. The pest could lower crop value (includes increasing crop production costs).

C. The pest could trigger the loss of markets (includes quarantines).

D. The pest could negatively change normal cultural practices.

E. The pest can vector, or is vectored, by another pestiferous organism.

F. The organism is injurious or poisonous to agriculturally important animals.

G. The organism can interfere with the delivery or supply of water for agricultural uses.

Economic Impact Score: 2

-Low (1) causes 0 or 1 of these impacts.

-Medium (2) causes 2 of these impacts.

-High (3) causes 3 or more of these impacts.

5) Environmental Impact: Risk is High (3) in California, as Arundo donax is an ecological transformer, it excludes native riparian species, leads to unshaded streams detrimental to migratory fish stocks, increases fire frequency, and degrades endangered species habitat (e.g., willow fly catcher).

Evaluate the environmental impact of the pest on California using the criteria below.

Environmental Impact Score: A, C, D

A. The pest could have a significant environmental impact such as lowering biodiversity, disrupting natural communities, or changing ecosystem processes.

B. The pest could directly affect threatened or endangered species.

C. The pest could impact threatened or endangered species by disrupting critical habitats.

D. The pest could trigger additional official or private treatment programs.

E. The pest significantly impacts cultural practices, home/urban gardening or ornamental plantings

Environmental Impact Score: 3

-Low (1) causes none of the above to occur

-Medium (2) causes one of the above to occur.

-High (3) causes two or more of the above to occur.

Consequences of Introduction to California for Arundo donaxRating (Score) High (13)

Low = 5-8 points

Medium = 9-12 points

High = 13-15 points

6) Post Entry Distribution and Survey Information: Arundo donax is widespread in CA. It receives a High (-3) in this category.

Evaluate the known distribution in California. Only official records identified by a taxonomic expert and supported by voucher specimens deposited in natural history collections should be considered. Pest incursions that have been eradicated, are under eradication, or have been delimited with no further detections should not be included.

-Not established (0) Pest never detected in California, or known only from incursions.

-Low (-1) Pest has a localized distribution in California, or is established in one suitable climate/host area (region).

-Medium (-2) Pest is widespread in California but not fully established in the endangered area, or pest established in two contiguous suitable climate/host areas.

-High (-3) Pest has fully established in the endangered area, or pest is reported in more than two contiguous or non-contiguous suitable climate/host areas.

The final score is the consequences of introduction score minus the post entry distribution and survey information score: Medium (10)


As this plant is well established as an invasive species in CA, there is little uncertainty associated with this assessement.

Conclusion and Rating Justification:

Based on the score listed above the pest is a high risk. This would justify an “A” rating if the species were not widely established in California. As the plant is found in over 50% of California counties, the pest would best be assigned a “B” or “C” rating. Many millions of dollars have been spent (by the state and other entities) to control Arundo donax in California. Many millions more will be spent in the near future. A “B” rating recognizes the large range of Arundo donax in California, but acknowledges the value of excluding it from new areas and preventing reinfestation of eradicated infestations.


Bell, G. P. 1997. Ecology and management of Arundo donax, and approaches to riparian habitat restoration in Southern California. In Plant Invasion: Studies from North America and Europe. J.H. Brock, M. Wade, P. Pysek and D. Green, eds. Leiden, the Netherlands: Backhuys, pp. 104-114.

Boose, A.B. and J.S. Holt. 1999. Environmental effects on asexual reproduction in Arundo donax. Weed Research 39:117-127.

Consortium of California Herbaria. Accessed 6/12/2014:

Goolsby, J. A., D. Spencer, and L. Whitehand. 2009. Pre-release assessment of impact on Arundo donax by the candidate biological control agents Tetramesa romana (Hymenoptera: Eurytomidae) and Rhizaspidiotus donacis (Hemiptera: Diaspididae) under quarantine conditions. Southwestern Entomologist 34:359-376.

Newhouser, M., C. Cornwall and R. Dale. 1999. Arundo: A Landowner Handbook. Accessed 6/12/2014:

Perdue, R.E. 1958. Arundo donax: source of musical reeds and industrial cellulose. Economic Botany 12:368-404.

Racelis, A.E., Goolsby, J., Moran, P.J. 2009. Seasonality and movement of adventive populations of the arundo wasp (Hymenoptera: Eurytomidae), a biological control agent of giant reed in the Lower Rio Grande Basin in south Texas. Southwestern Entomologist. 34(4):347-357.

USDA Arundo donax. Accessed 6/12/2014:

Weber, E. 2003. Invasive Plant Species of the World: A Reference Guide to Environmental Weeds. CABI Publishing, U.K. 4. Dudley, T., Department of Integrative Biology, University of California, Berkeley, USA and IUCN/SSC Invasive Species Specialist Group (ISSG). 2006. Arundo donax. Accessed 6/12/2014:

Wijte, A.H. B. M., T. Mizutani, E.R. Motamed, M.L. Merryfield, D.E. Miller and D.E. Alexander. 2005. Temperature and endogenous factors cause seasonal patterns in rooting by stem fragments of the invasive giant reed, Arundo donax (Poaceae). Int. J. Plant Sci. 166(3):507-517.

Responsible Party:

Dean G. Kelch, Primary Botanist; California Department of Food and Agriculture; 1220 N Street, Sacramento, CA 95814; Tel. (916) 403-6650;


Pest Rating: B  | Proposed Seed Rating: R

Posted by dk