• Highly destructive
  
• Competitive or
  
• Difficult to control using cultural or chemical (herbicide) practices

In more specific terms, a noxious weed is a plant that was introduced to Washington State that is difficult to control and damaging to our economy and natural resources.

• Reduce crop yields - noxious weeds compete with crop plants and can cost farmers time, labor, and money to control
  
• Destroy plant and animal habitat - many noxious weeds invade natural areas where they can outcompete native plants reducing biodiversity and threatening rare plants. Noxious weeds can displace native plants that provide food and shelter that wildlife depends on. Some noxious weeds not only outcompete plants, but they also change the physical or chemical properties of the environment so that native plants can no longer grow there.
  
• Reduce recreational opportunities - many aquatic noxious weeds choke waterways which reduces habitat for fish and other aquatic organisms. Choked waterways also makes it difficult for boaters, fishing enthusiasts, and swimmers. Invasive species reduce habitat and food for wildlife in wetland, rangeland, and forests.