The plant can grow about 4 inches a day and reach a mature height of 25 feet in about 12 months

A plant brought to California nearly 200 years ago has become a serious invasive weed in parts of the state. Giant reed, also known as arundo, was first planted in California in the 1820s to provide roofing material and help control erosion in the Los Angeles Basin.According to Center for invasive species research, the plant, scientifically known as Arundo donax, is native to eastern Asia. It was widely planted in different parts of the world because it could be used for several purposes, including walking sticks, fishing poles and musical instruments. It is also being investigated as a possible biofuel source.Over time, however, giant reed became an invasive weed in several regions where it was introduced. The University of California, Riverside’s Center for Invasive Species Research lists California among the areas where the plant has become a problem, along with parts of Texas, Hawaii, Nevada, Utah, Missouri, Virginia, New Mexico and Florida.One reason giant reed can spread so effectively is its rapid growth. The plant can grow about 4 inches a day and reach a mature height of 25 feet in about 12 months. It can also tolerate a range of environmental conditions, allowing it to grow in damp riparian areas and in moderately saline soils.

Dense growth pushes out native plants

Giant reed can form dense stands that leave little room for native vegetation. Native plants are typically displaced when arundo becomes established. Animals associated with those native plants may also be unable to use the dense stands of giant reed, leading to declines in their populations.The problem is particularly serious in California, where arundo can choke out native willows. Its presence also creates a fire risk because the plant can provide large amounts of fuel in riparian areas, where fires are typically uncommon.The plant is also well adapted to fire. This creates another problem because fires can help promote arundo invasions in sensitive habitats. In the Santa Ana River Basin in Southern California, the fire fuel load in riparian areas has almost tripled because of arundo infestations.The plant can create problems during floods as well. Large amounts of arundo can be dislodged and carried by floodwater. These pieces can form large rafts, and tons of the plant can build up around bridge supports. Such accumulations can cause bridges to collapse.

Giant reed also uses large amounts of water

The invasive plant’s impact is not limited to native vegetation and fire risk. Its water use has also been studied in the Santa Ana River.Research cited by the Center for Invasive Species Research estimated that arundo transpires 56,200 acre-feet of water each year on the Santa Ana River. Native vegetation was estimated to consume 18,700 acre-feet.The difference was estimated at 37,500 acre-feet of water. The study said that if arundo were not drawing this water from the Santa Ana River Basin, there would be enough water to serve a population of about 190,000 people.The same study estimated that purchasing that amount of untreated water from the Metropolitan Water Association would have cost approximately $12 million in 1993 dollars. The economic study was conducted in 1993.

Scientists studying ways to control it

Researchers at the University of California are studying the invasion ecology of arundo and different ways to control it. These include the use of herbicides and mechanical removal from areas where the plant has spread.Another approach being developed by USDA-ARS researchers in Texas is biological control. The strategy involves using natural enemies that feed on arundo and could reduce its growth.In California and other parts of the US, there are no organisms that cause substantial feeding damage or mortality to arundo. The lack of natural herbivores has partly allowed the plant to flourish in areas it has invaded.Researchers searching for arundo’s natural enemies in its native range have identified several insects that could potentially reduce the plant’s vigour by feeding on it. These include the Arundo wasp, Tetramesa romana; the Arundo scale, Rhizaspidiotus donacis; and the Arundo fly, Cryptonevra species.Safety evaluations have found that these insects are highly host-specific and pose no substantial threat to other plants. Efforts are now under way to mass rear these natural enemies and establish them in areas with severe arundo infestations.In North America, arundo appears to reproduce mainly through asexual reproduction. Although the plant produces flowers, it seldom produces viable seeds. Instead, it mainly spreads through vegetative reproduction, either through underground rhizomes or plant fragments.That ability to spread, combined with its rapid growth and dense stands, has helped turn a plant introduced to California in the 1820s for roofing material and erosion control into a long-term invasive species problem.