The economic cost of noxious weeds on Montana grazing lands

Authors: MANGOLD, JANE - Montana State University; FULLER, KATE - Montana State University; DAVIS, STACY - Montana State University; Rinella, Matthew - Matt

Submitted to: Invasive Plant Science and Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/24/2018
Publication Date: 6/4/2018
Citation: Mangold, J.M., Fuller, K.B., Davis, S.C., Rinella, M.J. 2018. The economic cost of noxious weeds on Montana grazing lands. Invasive Plant Science and Management. 11(2):96-100. https://doi.org/10.1017/inp.2018.10.
DOI: https://doi.org/10.1017/inp.2018.10

Interpretive Summary: We distributed a 16-question survey concerning noxious weed abundances, impacts and management to livestock producers grazing on privately-owned or leased grazing lands in Montana. The noxious weeds most commonly reported as being present on respondents’ grazing units were Canada thistle (64% of grazing units) and leafy spurge (45% of grazing units), and these species also reportedly caused the greatest reductions in livestock forage. Houndstongue was more prevalent than either spotted or diffuse knapweed (39% versus 32% and 10%, respectively, of grazing units), but collectively the knapweeds were reported to cause greater forage reductions than houndstongue. The top three strategies used to manage noxious weeds were chemical control, grazing, and biological control. Our estimates of economic losses are lower than many estimates from previous studies, possibly because we focused only on direct costs related to private grazing land while other studies often consider indirect impacts. Nonetheless, our estimates are substantial; for example our estimated loss equates to 24% of the average per-hectare lease rate for Montana grazing land.

Technical Abstract: We distributed a 16-question survey concerning noxious weed abundances, impacts and management to livestock producers grazing on privately-owned or leased grazing lands in Montana. The noxious weeds most commonly reported as being present on respondents’ grazing units were Canada thistle (64% of grazing units) and leafy spurge (45% of grazing units), and these species also reportedly caused the greatest reductions in livestock forage. Houndstongue was more prevalent than either spotted or diffuse knapweed (39% versus 32% and 10%, respectively, of grazing units), but collectively the knapweeds were reported to cause greater forage reductions than houndstongue. The top three strategies used to manage noxious weeds were chemical control, grazing, and biological control. Combining our survey responses with forage loss models derived from field data for spotted knapweed and leafy spurge, we estimated the combined cost of noxious weed management and forage losses on privately owned rangeland to be $3.54 ha-1 yr-1, or $7,243 annually for an average size grazing unit [i.e. 2,046 ha (5,055 ac)]. Our estimates of economic losses are lower than many estimates from previous studies, possibly because we focused only on direct costs related to private grazing land while other studies often consider indirect impacts. Nonetheless, our estimates are substantial; for example our estimated loss equates to 24% of the average per-hectare lease rate for Montana grazing land.