Invasive Plants and Weeds of the National Forests and Grasslands in the Southwestern Region

This second edition has been compiled to include additional nonnative, undesirable weeds that were left out of the first edition. Thirty-one additional species were added to reflect the concerns of forest personnel throughout the Southwestern Region.

As defined in Executive Order 13112, an “invasive species” (including plants) means an alien species whose introduction does or is likely to cause economic or environmental harm or harm to human health. Invasive plants are nonnative plant species that can grow and spread rapidly, thereby replacing native plant species. Invasive plants generally have one or more of the following characteristics: aggressiveness, difficult to manage, poisonous, toxic, parasitic, potential carrier or host for serious insects or diseases, and are new or uncommon to the United States or parts thereof. The definition of a weed is any undesired, uncultivated plant that grows out of place and competes with other plants for water, nutrients, and space.

Control of invasive plants and common weeds should be everyone’s concern since they can occur across all landownerships. Invasive plants and weeds compete with crops; poison or injure livestock, wildlife and people; reduce forage for wildlife and livestock; change natural fire regimes; and reduce recreation enjoyment because of thorns, allergies or unsightliness. Invasive plants and weeds also destroy the beauty and natural habitats of the Southwest wherever and whenever they occur.

Invasive plants continue to spread into uninfested areas in the western United States. On Federal lands, it is estimated that
invasive plants occur on more than 17 million acres. An estimated 6 to 7 million acres are currently infested on National Forest System lands, with a projected potential for increasing at a rate of 8 to 12 percent per year. Invasive plants and common weeds infest native plant communities in increasing numbers throughout the Southwest and are beginning to appear on the national forests and grasslands in greater numbers every passing year. Invasive plants have a significant environmental advantage over native plant species because they are free of natural enemies. Invasive plants pose an increasing threat to native ecosystems. This is why prevention and direct control methods must be used to stress or remove invasive plants and weeds from native plant communities.

The invasive plants listed in this document have been introduced to the Southwest from another place without the accompaniment of their natural predators or environmental controls to keep them in check. As a result, these plants can overwhelm native plant species and ecosystems, and spread dramatically year by year.

Control of invasive plant and common weed infestations requires the development and implementation of a management program, which focuses on: (1) preventing the introduction of new invasive plants and weeds; (2) early detection of infestations; (3) conducting early treatment of new infestations; and (4) containing and controlling established infestations at times and places that make them most effective and efficient. The most effective and efficient combination depends on factors such as the biology of the particular plant(s) and the circumstances under which it is growing. The overall priority for treatment is invasive plants over weeds, due to the greater threat of the former.

Because some invasive plants and common weeds pose challenges to land managers in dealing with the health of forests, woodlands, and grasslands, a series of weed management field guides has been published for management of invasive plant and common weed species in the Southwest. This book is a companion document intended to work in conjunction with those individual management field guides. The management field guides are available on our Forest Health Web site at:

This book serves as the U.S. Forest Service’s guide for identifying invasive plants and common weeds in forests, woodlands, grasslands, and deserts associated with its Southwestern Region. The Southwestern Region (Region 3) encompasses Arizona and New Mexico, which together have 11 national forests (NFs). The region also includes four national grasslands (NGs) located in northeastern New Mexico, western Oklahoma, and the Texas panhandle.

National Forests and Grasslands in Region 3 by State


New Mexico



Apache- Sitgreaves NFs
Coconino NF
Coronado NF
Kaibab NF
Prescott NF
Tonto NF

Carson NF
Cibola NF
Gila NF
Kiowa NG
Lincoln NF
Rita Blanca NG
Santa Fe NF

Black Kettle NG
Rita Blanca NG

Black Kettle NG
McClellan Creek NG
Rita Blanca NG


Map of Arizona, New Mexico, Oklahoma and Texas showing forest and grassland locations