Eradication is often stated as an essential element of weed management. Assessing the costs and benefits of eradication programs is often difficult because doing so requires speculation about the impacts and spread of weeds if eradication measures were not undertaken. The objective of this article is to describe and assess the Montana Dyer's Woad Cooperative Project, a program aimed at eradicating dyer's woad from Montana. The Project comprises four key components: early detection, treatment technologies, repeated site visits with monitoring, and education. To evaluate the success of the Montana Dyer's Woad Cooperative Project, we used monitoring data to observe the change in the number of counties where dyer's woad is present, plotted the trend in population size over time, and evaluated change in infestation size. We also predicted population spread based on the 1999 population size and demographic characteristics of dyer's woad. Dyer's woad has been eradicated from 9 of 13 infested counties in Montana, and infestation sizes have decreased in the remaining infested counties. In some counties, a containment effort was needed in conjunction with repeated inventories and treatment applications to prevent spread while depleting the seedbank to the point where eradication is possible. If not for the Project, our analysis suggests that some dyer's woad populations might consist of millions of plants, potentially covering 39,021 ha in Montana and costing $1.9 million/yr to manage. In comparison, the Project has reduced the total area infested in Montana to 2.6 ha and cost the state only $142,000 for the past 7 yr of management. In Montana, dyer's woad eradication from individual counties has been successful because of persistence and ongoing cooperative efforts.

Understanding competition for soil nitrate between common shrub-steppe, potential reclamation species, and common invasive species is necessary to identify mechanisms associated with ecosystem invasion and can assist with developing weed management scenarios. We designed a field experiment to evaluate the differential competitive effects of the invasive annual grass downy brome, the invasive biennial forb dyer's woad, and the reclamation shrub prostrate kochia, on nitrate acquisition of the perennial grass crested wheatgrass, the native forb western yarrow, and the native shrub big sagebrush. Individual plants were grown in two-plant neighborhoods, and a K15NO3 tracer was injected into the soil between plants and recovered from leaf material after 5 to 11 d. We also evaluated neighbor effects on shoot and root growth, leaf carbon : nitrogen ratio, and leaf nitrogen concentrations to better understand how these traits are associated with differences in nitrate acquisition and nitrogen allocation among the three growth forms. Nitrate acquisitions by crested wheatgrass and western yarrow were significantly lower when competing with downy brome than with dyer's woad and prostrate kochia; however, competitors had similar, negative effects on nitrate acquisition by big sagebrush. Nitrate acquisition ratios between competing neighbors revealed that: (1) the grasses always acquired more nitrate than neighbors of a different growth form, (2) western yarrow was equally competitive with dyer's woad and prostrate kochia, and (3) all neighbors acquired more nitrate than big sagebrush. More successful competition for nitrate in the grasses was associated with greater specific root length. Compared to species of the same respective growth form, the two invasive weeds (downy brome and dyer's woad) and prostrate kochia always had significantly lower leaf carbon : nitrogen ratio, and greater leaf nitrogen concentration, which have been broadly correlated with leaf lifespan and nutrient use efficiency, and indicate differing strategies to persist in the semiarid shrub-steppe ecosystems.