Yorkshire Fog grows as a weed in most of North America (the US, Canada, and Mexico). The states of Delaware, Maryland, New Hampshire, New Jersey, Pennsylvania, and Virginia have declared yorkshire Fog a noxious weed, and it is considered invasive in North America, Hawaii, Australia, East Asia, and South America. It competes aggressively for water and soil nutrients, shades out the seedlings of native plants and contaminates crop seeds. What's more, it is considered poisonous to mammals. Hand pulling and mowing can reduce infestations. Herbicides are more effective with young plants or when flower heads are about to emerge.