Weed Prevention Areas: Protecting Montana from Invasive Weeds
Person in field with writing in notebook
Photo: S. Wood


Prevention strategies are not perfect and may only interrupt a percentage of weed introductions. Long-term protection of weed-free rangelands relies on continuous monitoring to detect and remove invasions as they establish. This is critical, as small weed populations can spread quickly. Successful detection of new weeds in WPAs includes the following steps:
  1. Establish high- and low-risk sites based on invasion susceptibility.
  2. Design early detection surveys based on the invading plant and the invasion risk of each site.
  3. Survey and re-survey sites based on an optimal frequency of re-surveillance.
  4. Develop a mapping process to record new invasions and document weed-free areas (see “Early Detection Surveys” below).
  5. Develop passive monitoring networks consisting of user groups that access remote areas (see “Early Detection Surveys” below).

Early Detection Surveys

Surveys that target areas with a high likelihood of weeds are purposely biased, which is an effective approach when the objective is to locate new infestations. However, unbiased surveys that target areas at lower risk of invasion—remote areas or sites with low human activity—are performed in WPAs as well. The land is re-checked every 5 to 10 years, depending on its likelihood of invasion by priority weeds.

Monitoring low-risk sites can discover new populations in unlikely areas while also mapping weed-free rangelands to define an ecological starting-point for protection and a base for comparison as prevention systems progress over time. A portion of new land area (about 5% to 10%) in WPAs is inventoried each year by designated survey personnel (Liberty County weed scout, below).

Range Rider and ATV
Photo: Liberty County Weed District

Range Riders

man sitting on horse looking at book

Range riders are experts at identifying weeds and have GPS experience, so they can assist WPA ranchers with early detection surveys.

Range riders
  • collect rancher knowledge on weed spread,
  • survey susceptible sites, and
  • help ranchers protect the weed-free status of their ranch.

Large weed-free areas are mapped by range riders (also called weed scouts) and prioritized for protection from weed spread.

Resource: Protection of prioritized rangelands from weed spread with range riders.

Monitoring Networks

Passive monitoring networks are organized in WPAs and comprised of citizens who regularly access remote areas like ranchers and hunters. These networks provide a framework for finding and reporting new invasions to county weed districts.

Call-to-action programs, for example, encourage hunters to report new invasions of spotted knapweed to local weed districts (see ad below for Blaine County). And rancher-designed brochures promote partnerships with hunters to maintain weed-free rangelands and wildlife habitat (see brochure on right).

Attention All Hunters call 357-3200

Weed-free Rangelands & Wildlife Habitat Brochure

rancher and hunter partnerships pamphlet
(click on image or here to view full brochure)

Hunters have a vested interest in protecting healthy rangelands that most wildlife depends on for survival. This brochure provides information on weed threats and actions hunters can take to minimize the risk of invasion.

Site maintained by the Center for Invasive Species Management