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Biological Resources

Weed Management

Noxious weeds are identified by the State of Utah Department of Agriculture which under state law requires land owners to control undesirable plant species. The BLM cooperates with the State’s efforts by treating or otherwise controlling those noxious weeds found on public lands.
The St. George Field Office has identified the following noxious weeds on public lands in Washington County: Scotch Thistle (Onopordum acanthium), Perennial Pepperweed (Lepidium latifolium), Hoary Cress (Cardaria draba), Silverleaf Nightshade (Solanum elaegnifolium), Yellow Starthistle (Centaurea solstitialis), Russian Knapweed (Centaurea repens), Poison Milkweed (Asclepias subverticillata), and Bindweed (Convolvulus arvensis). BLM also pursues suppression of Bull Thistle, Malta Starthistle and Tamerisk, which are not on the State’s list but are of considerable concern to land managers.
These weeds have the potential to dominate large land areas and adversely affect wildlife habitat, livestock production, outdoor recreation, and wildfire management.
The St. George Field Office currently has approximately 5,000 acres infested with Scotch thistle and hoary cress. Small infestations of the other noxious weeds are found at various locations throughout the Field Office. Each year, up to approximately $75,000 is spent to control these weeds by herbicides or mechanical methods.
Exotic invasive species include cheatgrass and red brome. In recent years these annual grasses have dramatically increased the incidence and spread of wildfires.  These grasses infect almost 100 percent of the St. George Field Office and are largely responsible for recent wildfires burning nearly 30 percent of the lands administered by this office. 
New methods to control these grasses are currently being investigated and some practical solutions will hopefully emerge. Herbicides and biological agents seem to hold the most promise at this time. In June of 2007, BLM published the four volume Final Programmatic Environmental Impact Statement (FES 07-21) entitled Vegetation Treatments Using Herbicides on Bureau of Land Management Lands in 17 Western States. The statement and an associated programmatic report analyze the impacts of using herbicides and non-herbicide treatments including fire, mechanical, manual, and biological controls to achieve desired plant communities necessary to enhance wildlife habitats, improve watersheds and water quality, and reduce the risk of devastating wildfires.
The St. George Field Office works with municipal, county, state, and other federal agencies and private cooperators through an Integrated Pest Management program to achieve results by reducing the spread of invasive exotic plants and noxious weeds. This program includes the identification, inventory, suppression and monitoring of undesirable plant populations. Public land users are encouraged to become acquainted with those species common to Washington County and to take action to ensure they do not contribute to their inadvertent spread. For more information on invasive and noxious weeds visit the national BLM website.

You Can Help!
Stop the Invasion
  • Learn to identify weeds.
  • Report weed infestations.
  • Avoid spreading seeds:
    • Stay on designated trails.
    • Do not walk, drive, or camp on weeds.
    • Clean all gear before entering and leaving an area.
  • Tell others.

Tamerisk, Tamerix ramosissma