Because it cannot compete with established plants, great mullein is no longer considered a serious agricultural weed and is easily crowded out in cultivation, except in areas where vegetation is sparse to begin with, such as Californian semi-desertic areas of the eastern Sierra Nevada. In such ecological contexts, it crowds out native herbs and grasses; its tendency to appear after forest fires also disturbs the normal ecological succession. Although not an agricultural threat, its presence can be very difficult completely to eradicate and is especially problematic in overgrazed pastures. The species is legally listed as a noxious weed in the American state of Colorado (Class C) and Hawaii, and the Australian state of Victoria (regionally prohibited in the West Gippsland region, and regionally controlled in several others).