To be published in: Noxious wildland weeds of California. C. Bossard, J. Randall, & M. Hoshovsky (Eds)

NOXIOUS WILDLAND WEEDS OF CALIFORNIA: ARUNDO DONAX
Tom L. Dudley
Department of Integrative Biology
University of California
Berkeley, CA 94720-3140
 
Phone: 510-643-3021
Fax: 510-643-6264
E-mail: tdudley@socrates.berkeley.edu
 
 
 

ARUNDO DONAX L. (GIANT REED, GIANT CANE) 

Status: CalEPPC List A-1 -- Most invasive and damaging, widespread; Considered noxious by CDF&G, County Flood Control Districts but not officially listed as Noxious

HOW DO I RECOGNIZE THIS?

Distinctive features: Robust perennial grass 3 to 10 meters (9 to 30 feet) tall, growing in many-stemmed cane-like clumps, spreading from horizontal rootstocks below the soil and often forming large colonies many meters across. Individual stems or culms are tough and hollow, divided by partitions at nodes like bamboo, from 1 to 4 centimeters (.5 - 1.5 inches) in diameter. Culms are unbranched or with single (rarely multiple) lateral branches from nodes. The pale green to blue-green leaves broadly clasp the stem with a heart-shaped base, about 2-6 cm wide at the base and tapering to the tip, up to 70 cm or more in length. Leaves are arranged alternately (not opposite each other) throughout culm, very distinctly two-ranked (in a single plane). Arundo produces a tall, plume-like flower-head at the upper tips of stems, the flowers closely packed in a cream to brown colored cluster borne from early spring to early fall. Culms may remain green throughout the year but often fade with semi-dormancy during the winter months or in drought. Arundo can be confused with cultivated bamboos and corn, and in earlier stages with some large-stature grasses such as Leymus (Ryegrass), and especially Phragmites (Common reed) which is <4 meters tall and has panicles <3 dm with long hairs between the florets.

Full description:

Perennial reeds < 9 m tall, stems erect, hollow and glabrous < 4 cm diam with somewhat swollen nodes; thick, fleshy rhizomes form creeping rootstocks, yielding dense colonies. Leaves cauline, sheaths > internodes, ligule thinly membranous and fringed with hairs; the blade <1 m, tapering 2-6 cm wide, flat or folded, the margins scabrous; leaves alternate and conspicuously two-ranked. Inflorescence as terminal panicle 3-6 dm with branches ascending, silver-cream-brown-purplish, the numerous spikelets laterally compressed; glumes > florets, membranous and 3-5 veined; florets 4-5, breaking above glumes; lemma 8-12 mm and hairy, nerves ending in slender teeth, the middle one forming an inconspicuous awn; palea < lemma, 3-5 mm; anthers 2.5-3 mm. It does not form viable achenes in North America. Three species of Arundo occur world-wide in tropical to warm temperate Old World (K.W. Allred in Hickman 1993). A. donax is naturalized and invasive in many regions, including southern Africa, sub-tropical U.S. through Mexico, Caribbean islands and South America, Pacific Islands, Australia, and SE Asia (Hafliger and Scholz 1981).

WHERE WOULD I FIND IT

The largest colonies occur in riparian areas and floodplains of medium- to large-sized streams, from wet sites to dry river banks far from permanent water. It tends to favor low gradient riparian areas (<2% grade) over steeper and smaller channels, but scattered colonies are found in moist sites or springs on steeper slopes. Populations also occur in the upper estuaries of coastal streams. Often found along drainage ditches, where they have been used for bank stabilization, and in other moist sites including residential areas where they are used horticulturally. While Arundo is usually associated with rivers which have been physically disturbed and dammed upstream, it also can colonize within native stands of cottonwoods, willows, and other riparian species, even growing in sites shaded by tree canopy. Plants establish primarily in streamside sites, but expand beyond margins of riparian vegetation.

Arundo has been the biggest problem in coastal river drainages of southern California, especially in the Santa Ana, Santa Margarita, Santa Clara, Tijuana and other major and minor watersheds where it sometimes occupies entire river channels from bank to bank (Jackson et al. 1994). It occurs, however, in nearly all regions of the state, and in Baja California, usually below 350 meters (ca. 1000 feet). Giant reed has invaded central California river valleys in San Luis Obispo and Monterey Counties, the San Francisco Bay Area, in the Sacramento and San Joaquin River valleys, and is also increasing in the North Coast region (Dudley and Collins 1995). Although not presently considered a problem in the California deserts, Arundo likely would survive in regularly watered areas of the lower elevation deserts, but does not appear to tolerate high elevation and continental environments where regular freezing occurs (Sunset 1967).

Soil preferences are very broad, as Arundo is known from coarse sands to gravelly soil to heavy clays and river sediments. It grows best in well drained soil with ample moisture, from freshwater to semi-saline soils at margins of brackish estuaries. In Egypt Rezk and Edany (1979) found that A. donax tolerates both higher and lower water table levels than Phragmites australis, which is native to California.

WHERE DID IT COME FROM? HOW DOES IT SPREAD?

Arundo donax is often considered indigenous to the Mediterranean Basin (TNC 1993, Hickman 1993) or to warmer regions of the Old World (Munz and Keck 1959, Robbins et al. 1951), but it is apparently an ancient introduction into Europe from the Indian sub-continent (G. Bell, pers. comm.). In Eurasia it similarly inhabits low gradient rivercourses and may provide useful wildlife habitat in greatly altered river deltas (Granval et al. 1993, He et al. 1991). Incidentally, this plant has played an important role in the development of music, as the cane was the source of the original Pan pipe or syrinx, and remains the source of reeds for woodwind instruments (Perdue 1958). Arundo was brought to North America quite early, as it was abundant by 1820 in the Los Angeles River, where it was harvested for roofing material and fodder (Robbins et al. 1951). Commercial plantations exist in California based on cane use for musical instrument production, and other commercial possibilities could be explored. Horticultural propagation is widely conducted, and varieties of Arundo are available and commonly used in gardens or for erosion control (Loewer 1995, Sunset 1967). Invasive populations almost certainly resulted from escapes and displacement of plants from managed habitats (V. Vartanian, pers. comm.).

WHAT PROBLEMS DOES IT CAUSE?

Arundo is hypothesized to displace native plants and associated wildlife species as a consequence of the massive stands it forms (Bell 1994); the mechanism of competition with native species is not established. It clearly becomes a dominant component of the flora, and was estimated to comprise 68% of the riparian vegetation in the Santa Ana River (Douthit 1994). Several special status species are associated with California�s semi-arid riparian zones, including Least Bell�s vireo, Southwestern willow flycatcher and Yellow-billed cuckoo, all of which would be negatively affected by the replacement of willow/cottonwood riparian vegetation by Giant reed (Frandsen and Jackson 1994, Dudley and Collins 1995). Such species require the habitat and food resources provided by native plants, which support more insects than does Arundo (Herrera 1997). Unlike native riparian plants, Arundo provides little shading to the in-stream habitat, leading to increased water temperatures and reduced habitat quality for aquatic wildlife (Hoshovsky 1988). At risk are protected species like Arroyo toad, Red-legged frog, Western pond turtle, Santa Ana sucker, Arroyo chub, Unarmored three-spined stickleback, Tidewater goby and Southern steelhead trout, among others (Franklin 1996). In the Sacramento-San Joaquin Delta region Arundo interferes with levee maintenance and wildlife habitat management (P. Perrine, pers. comm.).

Arundo is also suspected of altering hydrological regimes and reducing groundwater availability by transpiring large amounts of water from semi-arid aquifers (Iverson 1994). It alters channel morphology by retaining sediments and constricting flows, and in some cases may reduce stream navigability (V. Lake, pers. comm, TNC 1996). Dense growths present fire hazards, often near urbanized areas, more than doubling the available fuel for wildfires and promoting post-fire regeneration of even greater quantities of Giant reed (Scott 1994, Frandsen 1994). Uprooted plants also pose clean-up problems when deposited on banks or in downstream estuaries (Douce 1994) and during floods create hazards where trapped behind bridges and other structures.

HOW DOES IT REPRODUCE?

It appears that plants in North America do not produce viable seed, and seedlings are not observed in the field. Population expansion here occurs through vegetative reproduction, either from underground rhizome extension of a colony or from plant fragments carried downstream, primarily during floods, to become rooted and form new clones (Else 1996). Horticultural propagation is routinely done by planting rhizomes which readily establish, but stems with no basal material are less likely to root. Fresh stems form roots at nodes under laboratory conditions (T. Zimmerman and J. Bunn, unpub. data), and root formation does occur where an attached culm has fallen over and is in contact with the substrate.

WHAT IS ITS GROWTH PATTERN?

New shoots arise from rhizomes in nearly any season, but are most common during spring. Growth likewise occurs in all seasons, but is highly sensitive to temperature and moisture (Perdue 1958). During warm months with ample water Arundo culms are reported to attain growth rates of 0.7 meters per week or about 4 inches per day, putting it among the fastest growing terrestrial plants. Biomass production has been estimated at 8.3 tons dry weight per acre (Perdue 1958). Young stems rapidly achieve the diameter of mature canes with subsequent growth involving thickening of the walls (Perdue 1958). Age of individual culms is certainly more than one year and branching seems to represent stem growth in later years, while rhizomes show indeterminant growth. Branches also form when a stem is cut or laid over. Die-back is infrequently observed but culms fade or partially brown-out during winter, apparently becoming dormant under cold conditions. The outstanding growth trait of this plant is its extremely flexible ability to survive and grow at almost any time under a wide variety of environmental conditions.

HOW CAN I GET RID OF IT?

Mechanical removal: Minor infestations can be eradicated by manual methods, especially where sensitive native plants and wildlife may be damaged by other methods. Hand pulling works with new plants less than 2 meters in height, but care must be taken that all rhizome material is removed (Hoshovsky 1988). This may be most effective in loose soils, and after rains have made the substrate workable. Plants can be dug using hand tools (pick-ax, mattock and shovel), especially in combination with cutting of stems near the base with pruning shears, machete, or chainsaw. Stems and roots should be removed or burned on-site to avoid re-rooting, or a chipper can be used to reduce material although clogging by the fibrous material makes chipping difficult (R. Dale, pers. comm.). For larger infestations on accessible terrain, heavier tools (rotary brush-cutter, chainsaw or tractor-mounted mower) may facilitate biomass reduction followed by rhizome removal (or chemical treatment). Such methods may be of limited use on complex or sensitive terrain, or on slopes over 30 percent, and may interfere with re-establishment of native plants and animals (Hoshovsky 1988). Mechanical eradication is extremely difficult, even with use of a backhoe, as rhizomes buried under 1 to 3 meters of alluvium readily resprout (R. Dale, pers. comm., Else 1996). Removal of all such material is infeasible, especially where extensive soil disturbance would be disruptive.

Chemical Control: In many, if not all, situations it may be necessary to use chemical methods to achieve eradication, usually in combination with mechanical removal. The most common herbicidal treatment against Arundo is glyphosate, primarily in the form of Rodeo® which is approved for use in wetlands (Round-Up® can be used away from water). Because glyphosate is a broad-spectrum herbicide, care should be taken to avoid application or drift onto desirable vegetation. The standard treatment is a foliar spray application of 1.5% by volume glyphosate with a 0.5% v/v non-ionic surfactant (Monsanto 1992). Most effective application is post-flowering and pre-dormancy, usually late July to early October when plants are translocating nutrients into root and rhizomes (TNC 1996, N. Jackson, pers. comm.). Foliar uptake and kill may be achieved by spray application during active growth periods, primarily late spring through early fall (Monsanto 1992). Small patches can be treated from the ground using backpack or towed sprayers, and major infestations have been aerially sprayed using helicopters.

Direct treatment to cut culms can reduce herbicide costs and avoid drift onto desirable plants, with fair results year-round and best kill in fall (Else et al. 1996, V. Vartanian, pers. comm.). Concentrated glyphosate solution (50% to 100% Rodeo or RoundUp, or 27%-54% glyphosate) is applied to stems, cut within 5-10 cm (2-4 inches) of the substrate, by painting with a cloth-covered wand or a sponge, or spraying with a hand �mister�. It may be helpful to add a dye or food coloring to the solution to indicate treated material. Solution must be applied immediately following cutting because translocation ceases within minutes of cutting; a five minute maximum interval is suggested (TNC 1996). New growth is sensitive to herbicides, so a common alternative is to cut or mow a patch and allow regeneration, returning later (3 weeks to 3 months) to treat new growth when 1-2 meters tall by foliar spraying of glyphosate. Promoting regrowth causes nutrients to be drawn from the roots, potentially reducing the translocation of glyphosate to the roots (TNC 1996). With all methods follow-up assessment and treatment should be conducted, and some professional applicators suggest 6 return spot treatments over 6 months (J. Van Diepen, pers. comm.). Other chemical control methods have been tested, including Dowpon-C, 2,2 DPA, paraquat, and triclopyr compounds (e.g. Dow Chemical�s Garlon)(Arnold and Warren 1966, Horng and Leu 1979, Franklin 1996), but are not currently recommended due to labelling restrictions or lower efficacy.

Prescribed burning: In most circumstances burning of live or chemically-treated material should not be attempted, as it cannot kill the underground rhizomes and probably favors Giant reed regeneration over native riparian species (K. Gaffney, unpub. data). Burning in place is problematic because of the risks of uncontained fire, the possibility of damage to beneficial species and the difficulties of promoting fire through patchily-distributed stands. There may be some cases where burning of attached material can be done, but only if other means of reducing biomass cannot be carried out. Cut material is often burned on-site, subject to local fire regulations, because of the difficulty and expense involved in collecting and removing or chipping all material.

Biological control: No biological control agents have been introduced against Arundo donax, although some invertebrates are known to feed upon the grass in Eurasia/Africa (Hoshovsky 1988, El-Enany 1985). Insects and other pathogens are unlikely to be introduced because the plant is commercially used, and native invertebrates do not appear to feed on it. Vertebrate grazers such as cattle and sheep may be useful (Hoshovsky 1988, Wynd et al. 1948), and Angora goats have been partially successful in reducing Arundo and other brush in southern California (Daar 1983). Grazers are unlikely to reduce population size sufficiently to eliminate the risks posed. Likewise, management of native plants to increase competition with Arundo probably provides an insufficient level of regulation, and in fact seems to offer little resistance against the invading reeds.

Further Information