Gaining Strides Against a Giant Reed

The tenacious and aggressive weed known as Arundo donax, also called Carrizo cane and giant reed, can easily grow three to seven inches a day and reach a height of 30 feet. It’s such a pernicious nuisance that it is now the top target for entomologist John Goolsby, who works at the Agricultural Research Service (ARS) Beneficial Insects Research Laboratory in Weslaco, Texas.

Brought to North America in the 1600s from Mediterranean Europe, A. donax found many practical uses, including as baskets, roof thatching and fine-quality reeds for musical instruments. But its negative aspects have far outnumbered any positive traits.

For example, giant reed invades riparian habitats and irrigation canals, leading to loss of biodiversity, catastrophic stream bank erosion, and damage to bridges. It also necessitates costly chemical and mechanical controls along waterways, and it competes for water in arid regions. Arundo has been cited as a troublesome invasive weed in Kentucky, Virginia and other eastern states, the American Southwest, northern Mexico and the Rio Grande Valley.

Taking a high-tech approach to control, Goolsby and collaborators James Everitt, a rangeland scientist, and agricultural engineer Chenghai Yang are using remote sensing to delineate Arundo’s distribution and density along the Rio Grande and its tributaries. Working with Texas A&M University scientists, the Weslaco specialists are assessing how much water Arundo actually uses.

But the best option for long-term management of the weed may be biological control using insects from the native range of A. donax. So far, three insects—captured and identified by scientists at the ARS European Biological Control Laboratory in Montpellier, France—seem the most promising candidates.

Tetramesa romana, a wasp that’s harmless to humans and animals, feeds on new Arundo shoots and canes, while the wormlike larvae of Cryptonevra flies prefer to stick to the tightly-compacted new shoots. The flat-bodied scale insect known as Rhizaspidiotus donacis favors Arundo roots and tubers.

Read more about research on this and other invasive weeds in the July 2007 issue of Agricultural Research magazine.

ARS is the U.S. Department of Agriculture’s chief scientific research agency.