Montana State University

Montana Noxious Weed List is Restructured

March 12, 2010 -- MSU News Service

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The Montana Department of Agriculture has released a restructured noxious weed list. The list includes five categories of invasive plants, as opposed to four categories in the previous list. Three new plant species were added and one was removed.

The new noxious weed categories are sorted by priority: 1A, 1B, 2A, 2B, and 3. Weeds are placed into priorities based on how abundant and widespread the species is across the state. In Montana, priority 1A weeds are not present; priority 1B weeds have limited presence; priority 2A weeds are common in isolated areas; and priority 2B weeds are abundant and widespread in many counties. Priority 3 weeds are not noxious weeds, but regulated plants that have potential for significant negative economic and ecological impact. Control of Priority 3 weeds is not mandated, but intentional spread or sale of them is prohibited.

Management of Priority 1A and 1B weeds is a priority across the state. Prevention, education, and eradication, when detected, are the most cost-effective strategies for managing high priority weeds. Management objectives for 2A and 2B weeds are suppression, but may range from eradication to containment, depending on their prevalence in a given area. For example, a weed receives higher priority for management when it is less abundant, but as it becomes more abundant and widespread, management shifts towards containment and suppression. Management of abundant weeds is still necessary, but may be a lower priority than managing weeds that occur in small, isolated populations.

Because weed abundance varies greatly across regions of the state, local prioritization and management objectives may also vary across the state. For example, spotted knapweed is abundant and widespread in many counties of western Montana and management objectives are containment and suppression of existing infestations. However, spotted knapweed is not common in many counties of eastern Montana and management objectives are prevention, education, and eradication of small populations when detected.

The weeds added to the noxious weed list include curlyleaf pondweed (Potamogeton crispus), hydrilla (Hydrilla verticillata), and cheatgrass (Bromus tectorum). Curlyleaf pondweed is a submersed aquatic plant, native to Eurasia, Africa, and Australia, and introduced to U.S. waters in the mid-1880s by hobbyists who used it as an aquarium plant. Curlyleaf pondweed can form dense mats that may interfere with boating and other open water recreation activities. It is highly competitive and can displace native aquatic plants. Curlyleaf pondweed is a Priority 1B weed.

Like curlyleaf pondweed, hydrilla is a submersed aquatic plant that that can form dense mats and outcompete native aquatic plants. It is native to Asia and was widely spread across the world as part of the aquarium trade. It is currently not known to be present in Montana. Both curlyleaf pondweed and hydrilla can be spread from one body of water to another via plant fragments on boats, trailers, and other recreational equipment. Hydrilla is a Priority 3 weed.

Cheatgrass is an annual grass that has been present in Montana for decades, but has been increasing rapidly over the past several years. It is native to the Mediterranean region and was introduced to North America in the late 1800s. Since then, it has become widely established across the western U.S. and is problematic in crop-, range-, and wildlands. It can reduce plant community diversity, decrease forage and crop yield and quality, and alter fire regimes. Cheatgrass is a Priority 3 weed.

Common crupina (Crupina vulgaris) has been removed from the list. Although it has been on the noxious weed list for years in Montana and is a noxious weed in some nearby states, it has never been found in Montana. Observations and research suggest it is not likely to become established in Montana due to the absence of suitable habitat.

The complete restructured noxious weed list can be found at the Montana Department of Agriculture web site http://agr.mt.gov/.

Jane Mangold (406) 994-5513 or jane.mangold@montana.edu