Translate
Pampas grass identification and control
Information about the noxious weed Pampas grass. Pampas grass is also known by its Latin name, Cortaderia selloana.
About this weed
Pampas grass is a non-regulated Class C noxious weed. This means property owners are not required to control this species on their property, though it is encouraged.
Pampas grass is known as Cortaderia selloana and it is in the grass family. It is native to South America.
Why it's a problem
Pampas grass is able to outcompete desirable vegetation for resources and can thrive in a range of conditions. It has escaped cultivation in California and Oregon and dominates open habitats in some places. It also can present a fire hazard from the accumulation of dry material over time. The saw-toothed leaves can also cause injury to people.
Plant description
Pampas grass tolerates winter frost as well as warmer summers and moderate drought. It can inhabit a wide variety of habitats including pastures, roadsides, logged forests, coastal sand dunes, shrublands and wetlands. Pampas grass is a large perennial (2+ year life cycle) grass that grows in clumps called tussocks.
Traits of pampas grass include:
- Leaves are bluish-green, over 6 feet long with sharp edges and a notable midrib.
- The leaf sheath (wraps around the stalk) has hairs and a hairy ligule (membrane where the leaf blade meets the stalk).
- The flowering stems are stiff and grow 5 to 13 feet tall. They are usually equal to or slightly taller than the leaves.
- Flowers occur in dense plumes 1 to 3 feet long at stem tips. These plumes range in color from white, silver, cream, pink, and violet. Flowering typically occurs in late august through September but may flower in winter.
- Female and male plants must be in proximity to pollinate to produce viable seed.
- Seeds spread by wind and it can reproduce by root fragments in wet conditions. Each plant can produce several hundred thousand seeds annually.
Be aware of look-alike plants
Pampas grass looks very similar to jubata grass. The University of California’s WEED Research and Information Center has a helpful document detailing the differences between the two species.
It can also be confused with ravenna grass, a class B noxious weed.
What to do if you find it
Property owners in King County are not required to control pampas grass and we are not tracking infestations. The King County Noxious Weed Control Board encourages property owners to remove it where possible and avoid introducing it to new landscapes.
Prevention
Prevention is a much easier route than controlling a mature infestation. Seeds can be carried on shoes, clothing, tools and vehicles, so make sure to clean off after entering infested areas. Instead of planting pampas grass in gardens, consider alternatives such as Calamagrostis acutiflora ‘Karl Foerster’ or Stipa gigantean, giant needle grass.
Control methods
In areas with few weeds, it is important to act quickly before they become harder to control. Make a long-term plan as it often takes several years to get rid of most weeds. Start in the least infested areas first and then move into more heavily infested areas. To reduce costs and environmental impacts, please consider a combination of methods.
Personal protective gear is important when controlling pampas grass. The leaf edges are sharp so wear leather gloves and protective clothing.
Manual control
Cut and bag the flower heads prior to control to prevent spreading the seeds. Pulling and digging are effective methods. Remove the entire top section of the roots to prevent resprouting.
Cultural control
When controlling these plants, try to minimize soil disturbance which aids seed germination. Mulch bare ground to smother seeds and prevent growth. Consider replanting the area with non-invasive grasses and sedges to compete with any new pampas grass seedlings.
Chemical control
Larger patches most likely will need an herbicide treatment to be effective. Avoid spraying where herbicide may enter a waterway or wetland unless you are using a state-approved aquatic herbicide and have the required permits and licenses to do so. Use of pesticides in water is regulated in Washington state. See Washington Department of Ecology Aquatic Pesticide Permits for details. Always read the label before using herbicide and follow state and local regulations.
Spot treatments with glyphosate have been effective in summer or fall. The best time is before seed set in late summer. For large infestations, consider combining methods like cutting or burning before treating regrowth. This strategy will use less herbicide. Always monitor sites for any plants that resprout and need follow up treatment. For more specific herbicide recommendations, see the link to Pampasgrass and Jubatagrass information from the University of California WEED Research and Information Center.
Disposal instructions
Cut and bag the flower heads prior to control to prevent spreading seeds. Uprooted plants left on the soil may take root and regrow, so turn the clump upside down and expose the roots to the air to decompose.
Washington State Noxious Weed Control Board pamphlet on noxious weed disposal