Source: California Invasive Plant Council
URL of this page: http://www.cal-ipc.org/ip/management/ipcw/pages/detailreport.cfm@usernumber=8&surveynumber=182.php
Invasive Plants of California's Wildland
|Scientific name||Arundo donax|
|Additional name information:||(L.)|
|Common name||giant reed, giant cane|
|Synonymous scientific names||none known|
|Closely related California natives||0|
|Closely related California non-natives:||0|
|Listed||CalEPPC List A-1,CDFA noxious|
HOW DO I RECOGNIZE IT?
Giant reed (Arundo donax) is a robust perennial grass nine to thirty 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. First-year culms are unbranched, with single or multiple lateral branches from nodes in the second year. The pale green to blue-green leaves, which broadly clasp the stem with a heart-shaped base and taper to the tip, are up to two feet or more in length. Leaves are arranged alternately throughout the culm, distinctly two-ranked (in a single plane). Giant reed produces a tall, plume-like flowerhead at the upper tips of stems, the flowers closely packed in a cream to brown cluster borne from early summer to early fall. Culms may remain green throughout the year, but often fade with semi-dormancy during the winter months or in drought. Giant reed can be confused with cultivated bamboos and corn, and in earlier stages with some large-stature grasses such as Leymus (ryegrass), and especially with Phragmites (common reed), which is less than ten feet tall and has panicles less than one foot long with long hairs between the florets.
Inflorescence: as terminal panicle 1-2 ft (30-60 cm) with branches ascending, silver-cream-brown, the numerous spikelets laterally compressed; glumes > florets, membranous and 3-5 veined; florets 4-5, breaking above glumes; lemma 0.3-0.5 in (8-12 mm) and hairy, nerves ending in slender teeth, the middle forming an inconspicuous awn; palea < lemma, 0.12-0.2 in (3-5 mm); anthers 0.1-0.12 in (2.5-3 mm). It does not form viable achenes in North America (Hickman 1993).
|WHERE WOULD I FIND IT?||
Giant reed occurs in central and southern California and in Baja California, usually below 1,000 feet (350 m) elevation. It has invaded central California river valleys in San Luis Obispo and Monterey counties, the San Francisco Bay Area, and in the Sacramento and San Joaquin River valleys, and is also increasing in the North Coast region (Dudley and Collins 1995). Giant reed has been the most serious 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, Bell 1998). Although not currently considered a problem in California deserts, giant reed survives in regularly watered areas of lower-elevation deserts, but does not appear to tolerate high-elevation and continental environments where regular freezing occurs (Sunset 1967). Giant reed is naturalized and invasive in many regions, including southern Africa, subtropical United States through Mexico, the Caribbean islands and South America, Pacific Islands, Australia, and Southeast Asia (Hafliger and Scholz 1981). In California, the largest colonies occur in riparian areas and floodplains of medium-sized to large streams, from wet sites to dry river banks far from permanent water. Giant reed tends to favor low-gradient (less that 2 percent) riparian areas 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. It is often found along drainage ditches, where the plant has been used for bank stabilization, and in other moist sites, including residential areas where giant reed is used horticulturally. While it is usually associated with rivers that have been physically disturbed and dammed upstream, giant reed 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 the margins of riparian vegetation. Soil preferences are broad, as giant reed 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 Arundo donax tolerates both higher and lower water table levels than Phragmites australis, which is native to California.
|WHERE DID IT COME FROM AND HOW IS IT SPREAD?||
Three species of Arundo occur worldwide in tropical to
warm temperate regions. A. donax is often considered indigenous to the
Mediterranean Basin (Hickman 1993) or to warmer regions of the Old World, but
apparently it is an ancient introduction into Europe from the Indian
sub-continent (Bell 1998). In Eurasia it similarly inhabits low-gradient river
courses and may provide useful wildlife habitat in greatly altered river deltas
(Granval et al. 1993, He 1991).
|WHAT PROBLEMS DOES IT CAUSE?||
Giant reed displaces native plants and associated wildlife
species because of the massive stands it forms (Bell 1994, Gaffney and Cushman
1998). Competition with native species has been shown to result from
monopolization of soil moisture and by shading (Dudley unpubl. data). It clearly
becomes a dominant component of the flora, and was estimated to comprise 68
percent of the riparian vegetation in the Santa Ana River (Douthit 1994). As
giant reed replaces riparian vegetation in semi-arid zones, it reduces habitat
and food supply, particularly insect populations, for several special status
species such as least Bell's vireo, southwestern willow flycatcher, and
yellow-billed cuckoo (Frandsen and Jackson 1994, Dudley and Collins 1995).
Unlike native riparian plants, giant reed provides little shading to the
in-stream habitat, leading to increased water temperatures and reduced habitat
quality for aquatic wildlife. At risk are protected species such as 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
donax interferes with levee maintenance and wildlife habitat management
(Perrine, pers. comm.).
|HOW DOES IT GROW AND REPRODUCE?||
Plants in North America do not appear to produce viable
seed, and seedlings are not seen 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.
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, but
survival is poor (Zimmerman and Bunn unpubl. data), and root formation
does occur where an attached culm has fallen over and is in contact with
|HOW CAN I GET RID OF IT?||
Studies of giant reed invasion in California are underway, so more data on its biology and management will be available soon. For further information about monitoring and managing infestations, contact Team Arundo in southern California or Team Arundo del Norte in central and northern parts of the state (see Resources section).
Manual methods: Minor infestations can be
eradicated by manual methods, especially where sensitive native plants and
wildlife may be damaged by other methods. Hand pulling is effective with new
plants less than six feet (2 m) in height, but care must be taken that all
rhizome material is removed. This may be most effective in loose soils and after
rains have made the substrate workable. Plants can be dug up 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 (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 reestablishment of native plants and
Insects and fungi: No
biological control agents against Arundo donax have been approved by the
USDA, although some invertebrates are known to feed on the grass in
Eurasia/Africa (Tracy and DeLoach 1999). The green bug (Schizaphiz
graminum) has been observed to feed on giant reed in winter (Zuniga et al.
1983). In France Phothedes dulcis caterpillars may feed on it. The insect
Zyginidia guyumi uses giant reed as an important food source in Pakistan
(Ahmed et al. 1977). A moth borer (Diatraea saccharalis) has been
reported to attack it in Barbados. A USDA evaluation of the potential benefits
of biological control against giant reed ranked it as a promising candidate and
suggested several insects and pathogens as possible control agents (Tracy and
In many, if not all, situations it may be
necessary to use chemical methods to achieve eradication, especially in
combination with mechanical removal. The most common herbicidal treatment
against giant reed 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 percent by volume glyphosate with a 0.5 percent
non-ionic surfactant (Monsanto 1992). Most effective application is
post-flowering and pre-dormancy, usually late August to early November when
plants are translocating nutrients into root and rhizomes (TNC 1996). 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.