These weeds are typically agricultural pests, though many also have impacts on natural areas. Many noxious weeds have come to new regions and countries through contaminated shipments of feed and crop seeds or intentional introductions such as ornamental plants for horticultural use.
There is controversy about the definition of weed as well as the definition of noxious weed, particularly when it comes to how agricultural interests relate to conservationism. Some "noxious weeds", such as ragwort, produce copious amounts of nectar, valuable for the survival of bees and other pollinators, or other advantages like larval host foods and habitats. Wild parsnip, Pastinaca sativa, for instance, provides large tubular stems that some bee species hibernate in, larval food for two different swallowtail butterflies, and other beneficial qualities. One study of restoration meadows using commercial mixes found that several weeds greatly outperformed, in terms of nectar production, the top-performing annual flower planted for meadow restoration in the meadows studied (cornflower). The best performers also quite significantly outperformed the top-performing perennial that wasn't classified as a weed (rough hawkbit). The farming practice of using beetle banks may also complicate the nature of dubbing certain plants noxious weeds, due to their beneficial qualities in that role.
There are types of noxious weeds that are harmful or poisonous to humans, domesticated grazing animals, and wildlife. Open fields and grazing pastures with disturbed soils and open sunlight are often more susceptible. Protecting grazing animals from toxic weeds in their primary feeding areas is therefore important.
Some guidelines to prevent the spread of noxious weeds are:
Maintaining control of noxious weeds is important for the health of habitats, livestock, wildlife and native plants, and of humans of all ages. How to control noxious weeds depends on the surrounding environment and habitats, the weed species, the availability of equipment, labor, supplies, and financial resources. Laws often require that noxious weed control funding from governmental agencies must be used for eradication, invasion prevention, or native habitat and plant community restoration project scopes.