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2012-10-04

Aliens invade City Park

By Carolyn B. Edwards BCC Staff Writer

It's an alien invasion nobody wants, whatever their political persuasion. Local experts have spotted a dominant clump of Arundo donax in Bandera's City Park.

The giant reed is an exotic plant that probably arrived in North America from Asia in the early 1800s.

It is native to a large number of countries in the Mediterranean area, from Spain in the west, into Africa and east into Iraq.

This rather mild-mannered plant resembles bamboo and native canes with its hollow tubular stalks and long, narrow leaves. As a result, it appears to have slipped under the radar as a threatening species until recently. In fact, its spread may be largely blamed on human use of the plant as an ornamental in the landscape and for erosion control.

According to the USDA, A. donax's invasiveness is well-documented in California and Texas, where it has been declared a "noxious weed." Water loss to A. donax is already a critical factor in areas along the Rio Grande River and is rapidly spreading along other Texas river basins.

The plant is considered a national security issue along our southern border because infrared sensors cannot detect heat beneath the plant's thick canopy. It is also responsible for habitat destruction and species displacement.

This perennial grass can grow over 20 feet in height. Its tough, fibrous roots penetrate deeply into the soil.

It's one bad boy

Texasinvasives.org classifies the weed as a severe ecological threat that "chokes stream channels, crowds out native plants, interferes with flood control, increases fire potential and reduces habitat for wildlife." As it flourishes along river and creek banks, it narrows the water channels, increasing sedimentation, flooding and erosion.

Not only has the Texas Department of Agriculture declared A. donax a noxious weed, Texas Parks and Wildlife has made it a "Prohibited Exotic Species." The plant is also classified a noxious weed on the federal level.

The exotic has spread nationwide from California to Florida, and from Texas in the south to as far north as Missouri.

The root masses collect debris, blocking culverts and damaging bridges and dams.

It creates a fire hazard because it ignites easily and burns intensely.

The plant reproduces mostly through its rhizomes which root and sprout readily. A. donax can root from a rhizome piece as small as one inch.

Pieces can float miles downstream, take root and quickly invade a new area.

The giant reed likes moist places, but will tolerate a wide variety of conditions and soil types.

Texasinvasives.org suggests using native plant species such as square-stem spikerush, sugarcane plumegrass, powdery thalia, big bluestem, bushy beardgrass, switchgrass or eastern gama grass for restoration projects in landscapes and for erosion control.

Control - iffy at best

While mechanical control such as repeated mowing or tilling may be somewhat effective, any fragments of root left in the soil will lead to reestablishment.

The best way to control small outcroppings of the weed appears to be the application of systemic herbicides, such as glyphosate. The herbicide should be applied after flowering, either on the cut stumps or sprayed on the foliage. Repeat applications will most likely be needed.

Extreme care should be taken when applying herbicides around water sources or wetlands to avoid harming aquatic plants and animals. Use a product that is safe for such application. The safety of the person doing the application should also be considered with these toxic chemicals.

"Arundo donax is a tough plant that is going to cause a lot of damage to our resources as it spreads," said Bandera River Authority General Manager David Mauk. Mauk plans to pursue grants that could help fight this pernicious pest. In addition to Bandera City Park, other outbreaks of the plant have been found in the county.

The Nueces River Authority is currently studying the spread and control of the noxious pest in their river basin.

Prescribed burning may also be an effective treatment if done after flowering.

According to an abstract by Texas A&M Department of Agriculture scientists Seawright, Rister, Lacewell, Sturdivant, Goolsby and McCorkle in 2009, A. donax consumes "as much as 528 gallons [of water] per square meter."

They report that the USDA is investigating the use of biological controls. Studies of A. donax in its native habitat have revealed four insect species that appear to exercise some control over the plant: a wasp, scale insects, a fly and a leafminer. In 2009, the USDA was in the process of receiving permission to release two of those insects in the Rio Grande Valley.

In addition to all of its other bad manners, A. donax has also been found to be a moderate allergen that pollinates all year long!

The University of Florida Extension Service reports that commercially produced giant reed grown in the Mediterranean is used to make reeds for musical instruments. Scientists interested in bioenergy are looking at possible uses of the plant in that field because of its ability to quickly provide high amounts of biomass.