Economic Evaluation of Spotted Knapweed [Centaurea maculosa] Control Using Picloram

Abstract

Spotted knapweed is the most serious range weed problem in western Montana. Although picloram is often used to control knapweed, the economic feasibility of the practice has not been evaluated. We developed a model to economically evaluate spotted knapweed control on rangeland. Model functions describing the dynamics of the plant community preceding and following treatment were derived from field observations in western Montana. Economic returns per management unit were calculated for 3 scenarios: (1) no treatment, (2) containment, and (3) eradication of spotted knapweed. After tax costs and benefits of treatments were analyzed for a 20-year period and discounted to the present. An economic loss in current dollars of S2.38/ha was incurred under the no treatment strategy when 25% of the management unit was initiaily inlested with spotted knapweed and the weed was spreading to new acres and replacing desirable forage. After-tax present value of added AUMs in the eradication strategy was greater than the after-tax present value of added costs, S3.41/ha and Sl .99/ha, respectively. As site productivity, value of an AUM, and rate of knapweed spread to new acres increased, economic returns increased relative to treatment costs. In contrast, herbicide treatment became leas cost-effective as knapweed utilization by livestock increased. Thus, economic feasibility of spotted knapweed control varied with economic and biologic conditions.

Influence of Density on Intermediate Wheatgrass and Spotted Knapweed Interference

“…In areas where residual plant species are absent, herbicides (Davis et al 1993, Griffith andLacey 1991), natural enemies (Story et al 1991, Cuda et al 1989), or sheep grazing (Olson et al 1997) do not provide long-term control of spotted knapweed because desirable species are not available to occupy niches opened by the control procedure. In these areas, establishing competitive plants is essential for successional management of spotted knapweed and the restoration of desirable plant communities .…”

Soil Fungi Alter Interactions Between the Invader Centaurea Maculosa and North American Natives

“…While relatively rare in its native communities, Centaurea maculosa is among the most widespread and destructive grassland invaders in the Western United States and Canada (Griffith andLucey 1991, Sheley andJacobs 1997). The negative effects of Centaurea species on native plants are well documented (Muir andMajak 1983, Lesica andShelly 1996) and C. maculosa may reduce the cover and diversity of native grassland species by more than 90% (Ridenour and Callaway 2001).…”

Mycorrhizae Indirectly Enhance Competitive Effects of an Invasive Forb on a Native Bunchgrass

“…Centaurea maculosa Lam. (Asteraceae) and others in its genus are among the most economically destructive range weeds in western North America (Watson andRenney 1974, Griffith andLucey 1991). Despite extensive efforts to eradicate them, Centaurea species are spreading at prodigious rates (Muller-Scharer and Schroeder 1993).…”