Invasive Plants

Invasive Plants Impact Us All

We should all care about the impact of invasive plants on public and private lands.  Invasive/noxious plants threaten native species and habitats by competing for critical and often limited resources such as sunlight, water, nutrients, soil and space.  Noxious weeds can be costly to all Arizonans by adversely affecting our agriculture, economics, environment, wildlife, recreation, and health. Their impact to the U.S. economy is believe to exceed $30 billion dollars annually. 

What are Invasive Species?

Giant Reed, an invasive plant specie found along waterwaysInvasive species have been characterized as a “catastrophic wildfire in slow motion.” Thousands of non-native invasive plants, insects, fish, mollusks, crustaceans, pathogens, mammals, birds, reptiles, and amphibians have infested hundreds of millions of acres of land and water across the Nation, causing massive disruptions in ecosystem function, reducing biopersity, and degrading ecosystem health in our Nation’s forests, prairies, mountains, wetlands, rivers, and oceans. Invasive organisms affect the health of not only the Nation’s forests and rangelands but also of wildlife, livestock, fish, and humans.

A species is considered invasive if it meets these two criteria:

  1. It is nonnative to the ecosystem under consideration, and
  2. Its introduction causes or is likely to cause economic or environmental harm or harm to human health.

Where did these invasive weeds come from?

"Most weeds originally were spread from the Middle East to Europe, colonizing ground disturbed by agriculture , grazing, and  urban development. When European colonists journeyed overseas, they inadvertently transported weeds with them  in their grain seed, livestock feed, and ship ballasts.  From the New World ports, weeds hitched rides inland with pioneers, set seed in America’s farm fields and rangelands, and began to spread like a slow-moving fire." (Noxious Weeds: a Disaster Looking for a Place to Happen in Arizona!!; Larry D. Howery, George Ruyle, Arizona AgNIC, 1996; Retrieved 12/03/14 from

Controlling Invasive Plants 

The goal of the USDA Forest Service Invasive Species Program is to reduce, minimize, or eliminate the potential for introduction, establishment, spread, and impact of invasive species across all landscapes and ownerships.

Tamarix in bloom, a green shrub with purple flowersInvasive Weeds Threaten Your Forest

On the Prescott National Forest, Dalmatian toadflax, tamarisk, spotted knapweed, bull thistle, scotch thistle, Russian olive ,and many other invasive/noxious weeds are found. To help you identify invasive/noxious weeds, the PNF is featuring 4 weeds a year (one every 3 months) on this web page.  

Weed of the Quarter: Salt Cedar (Tamarix)

Salt Cedar (Tamarix) is an invasive plant that thrives along Central Arizona's waterways, using lots of water, crowding out native species, and taking over beaches. Tamarix are persistent plants; and dense, impenetrable stands of tamarix can displace desirable vegetation. 

Weed-of-the-Quarter for April through June is Tamarix 

Please, Report Invasive Weeds

If you see weeds on the forest, please let us know by calling or visiting your local ranger station.  Please note the  species of the plant and the exact location by GPS or Lat & Long coordinates or mark the location on a map.

Interested in Volunteering?

If you would like to help manage invasive weeds on the forest, please contact the Invasive Weed  Manager at 928-777-2200.

US Forest Service Volunteer PatchWhen and where are weeds chemically treated on the forest?

Toll-free Information: (866) 449-7809

Want to Learn More?

More information about invasive weeds is available at the following websites:

  • USDA Forest Service Invasive Species Program This website gives a more detailed description of the many ways invasive species travel and how we can help by not picking up these "hitchhikers."
  • US Forest Service Southwestern Region Forest and Grassland Health  Hazard trees, insects and disease, weed field guides, publications, and current highlights in forest lands in Arizona and New Mexico.  This site is loaded with information.
  • University of Arizona Cooperative Extension Arizona's main academic research institution for all things agricultural--including invasive weeds.  Here you'll find research papers (geared toward a non-academic audience) and photos of the invasive plants that threaten forests in Arizona.
  • USFS Southwestern Region Invasive Species Field Guides: Photos and detailed descriptions of invasive weeds in Arizona and New Mexico
  • Friends of the Verde River Greenway restores, preserves and promotes the natural, cultural, scenic and recreational resources of the Verde River and its tributaries.  Their website has a very nice slide show of river scenery!
  • Verde Watershed Restoration Coalition Vision: For the Verde River and its tributaries to comprise a perse, self-sustaining, and resilient riparian ecosystem in which invasive plant species are controlled through cooperative stakeholder participation.  Visit this site to see which plants threaten the Verde River, what is being done about it, and how you can help!
  • Invasive Plant Atlas of the United States Lots of good information here: species information, tools and training, distribution maps, and ways that you can contribute to mapping invasive species.  This site even has information about how a smart phone can document invasive species while you're out enjoying your public lands. Check it out!
  •  is another resource that is loaded with good information including an exhaustive list of invasive species by state as well as nation-wide.