Friday, July 25, 2008

By Noel Mues

Recently, the Nebraska Department of Agriculture declared the non-native phragmites (Common Reed) an official noxious weed. The statewide designation, which takes effect immediately, is an expansion of a temporary designation issued last year for phragmites within the Republican River basin.

Greg Ibach, Director of the Nebraska Department of Agriculture, has the authority to issue temporary designations under the Noxious Weed Control Act. The temporary designation will expire in February 2009. Ibach said he anticipates moving ahead with the formal process to add phragmites to the permanent noxious weed list before then.

Differences in Native and Introduced Phragmites Populations – The non-native or introduced   phragmites population is a more serious problem than the native genotypes.

In general, native populations appear to have a lower stem density, and produce a reddish-purple color on their stems and ligules in spring and summer that is not present in non-native populations. During winter the red stems turn light to chestnut brown and somewhat gray. Stems of native genotypes are smooth and shiny as if polished, particularly in the winter, while stems of introduced genotypes are dull, rough and ribbed. These differences are easy to recognize by running your fingers up and down the stems.

In instances where native and introduced clones grow in close proximity of each other, differences in stem density and stem toughness become obvious on windy days. Introduced genotypes remain sturdy and erect and move little while native genotypes easily bend and swing in the wind.

In the fall and winter, differences in the density of inflorescences are also obvious; introduced genotypes appear to have much denser and larger inflorescences.

Excavations of rhizomes at several sites have also produced consistent differences between native and introduced genotypes. Native genotypes have round rhizomes that are yellow and rhizome diameters of less than 15mm. Rhizomes of introduced genotypes, particularly when freshly excavated and rinsed are white. Although there are some rhizomes with diameters <15mm, most rhizome diameters in introduced genotypes are larger than 15mm.

Ibach said the statewide noxious weed designation is necessary to help county weed control officials work with landowners to address areas of high infestation and to prevent further spread of this invasive species. Phragmites is primarily found along Nebraska’s rivers, streams, floodplains and lakeshores.

“In order to be good stewards of the land, we need to protect our natural resources from non-native plants that have no value and that will, absent control measures, continue to invade our river systems,” Ibach said. “The designation is an important tool for weed control officials who are working on projects to control phragmites.”

According to Mitch Coffin, NDA Noxious Weed Program manager, phragmites can quickly form a monoculture and displace native riparian plants, grasses and forbs. Once phragmites matures, it sends out rhizomes searching for water; these rhizomes can stretch as much as 30 feet in search of water. Phragmites can grow to 20 feet tall.

Other officially designated noxious weeds in Nebraska include: Saltcedar, Canada thistle, leafy spurge, musk thistle, plumeless thistle, purple loosestrife and spotted and diffuse knapweed.

For more information about the phragmites designation contact your local University of Nebraska-Lincoln Extension Office, County Weed Control Superintendent, or questions may be directed to NDA officials at (402) 471-6844.