A
noxious weed or
injurious weed is a
weed that has been designated by an agricultural authority as one that is injurious to
agricultural or
horticultural crops, natural
habitats or
ecosystems, or humans or
livestock. Most noxious weeds have been
introduced into an ecosystem by ignorance, mismanagement, or accident. Some noxious weeds are native. Typically they are plants that grow aggressively, multiply quickly without natural controls (native herbivores, soil chemistry, etc.), and display adverse effects through contact or ingestion. Noxious weeds are a large problem in many parts of the world, greatly affecting areas of
agriculture,
forest management,
nature reserves,
parks and other open space.