Herbicides were applied to four west-central Montana sites with light to moderate spotted knapweed (Centaurea maculosa Lam.) infestations. Althought knapweed suppression was high, 2 years after the spraying the communities were not converted to grass monocultures. No large declines in plant diversity were caused by the herbicides, and small depressions were probably transitory. By the third year, diversity had increased.
United States Department of Agriculture, Forest Service, "Plant Community Diversity After Herbicide Control of Spotted Knapweed" (1992). Herbicides and Pesticides. Paper 1.