What is an unwanted or noxious weed?

Plants that hurt animals and keep good native plants from growing are noxious weeds. These bad plants take the sunshine, drink the water, and use the food in the soil, leaving little for the good plants. Good plants that feed our sheep, cattle and horses cannot live. When the good plants are gone our animals have nothing to eat. Some bad plants have stickers that cause sores on their feet, mouth, ears, and eyes. Noxious weeds hurt livestock with the stickers or poison. If animals have no edible plants they will eat weeds that make them sick or die.