A new statewide noxious weed list took effect recently, with changes designed to highlight bad actors that state and county weed officials don’t want to see take root in Montana.

Earlier weed listings were difficult to explain in part because the newest and most threatening weed species were in categories with higher numbers that might imply a low priority for control efforts.

“It was counter-intuitive, and not a system used by our surrounding states,” Ron de Yong, director of the Montana Department of Agriculture, said. Western states have begun to work more closely together in efforts to limit the spread of invasive species including weeds, and the switch to a priority rating should help in that regard. The priority ratings also will help counties to focus their attention on weeds that can and should be eradicated, and to prioritize suppression efforts among weeds that are more abundant. Priorities 1A and 1B are reserved for weeds not now present or with limited presence in Montana, and which can often be eradicated before they spread, says Dave Burch, weed program manager with the department.

Priority 2A is used for weeds that are common in some areas. Efforts against these species, which include tansy ragwort, hawkweeds, tall buttercup and yellowflag iris, can be prioritized by local weed districts. Priority 2B weeds such as Canada thistle, field bindweed and spotted knapweed are abundant in Montana, again allowing local officials to prioritize control efforts.

An example of the need for prioritization is leafy spurge, which is common in eastern Montana rangelands but found only in isolated pockets in western Montana, Burch says. Eradicating or halting the spread of such weeds in isolated areas can pay dividends against the difficult-to-control species, which costs the state millions of dollars in control costs, lost forage for livestock and wildlife and environmental damage to native species.

A committee of local, tribal, state and university officials devised the priorities over a two-year period. The committee also created a Priority 3 for weeds such as cheatgrass (downy brome) that pose significant negative impacts and are often spread as contaminants in agricultural products. The committee recommended research and education to limit the spread of these regulated plants.

Also on the Priority 3 list is hydrilla, a common aquatic plant in aquariums. Idaho has found that the plant is adapting to cooler water, Burch says. Hydrilla was included on the Priority 3 list to encourage education to prevent aquarium owners from tossing the plants where they might thrive and enter streams and lakes.

Under the new system, landowners still are required to take measures to prevent the propagation and spread of noxious weeds, Burch said. For residential landowners, this is frequently done by mowing, pulling or chemically treating plants or weed patches. County weed officials can provide information on the most effective means to control noxious weeds in their areas.

The entire weed list is found on the department’s Web site at: http://agr.mt.gov/weedpest/noxiousweedlist.asp. For more information about the priority rating system, contact a county weed official or Dave Burch at 406-444-3144 or by e-mail at dburch@mt.gov.