Suppressing Canada Thistle Establishment with Native Seed Mixes and Resulting Cost Analysis

Abstract

Canada thistle (Cirsium arvense) on conservation lands is costly and diminishes conservation objectives. This project was designed to control Canada thistle by spiking native seed mixtures. Spiking is where a native seed mixture had 3-5 native forbs that are functionally similar to Canada thistle at 3-10 times the recommended seeding density added to it. The project consisted of small-scale experiments on lands in eastern North Dakota and large-scale experiments on U.S. Fish and Wildlife land in eastern North and South Dakota. The results show that the spiked method reduced the establishment of Canada thistle immediately after seeding. The cost analysis showed the spike method was equal or lower in cost compared to herbicide control if herbicide control is: 1) 25% or less effective, 2) logistically problematic, 3) operationally more costly, 4) needed on two-thirds of the area, and 5) producing a high risk of affecting non-target species.