Encycloweedia: Weed Ratings
A noxious weed is a plant that has been defined as a pest by law or regulation. Both California and the U.S government maintain lists of plants that are considered threats to the well being of the state or the country. The two lists differ significantly.
In California, biologists of the California Department of Food and Agriculture recommend plants for listing, after consultation with outside experts and the Agricultural Commissioners of California's counties (CACs). If a plant is found to probably be "troublesome, aggressive, intrusive, detrimental, or destructive to agriculture, silviculture, or important native species, and difficult to control or eradicate", the Department will designate the plant as a noxious weed.
At the time that CDFA lists a species, it also receives a rating of A, B, C, D, or Q. These ratings reflect CDFA's view of the statewide importance of the pest, the likelihood that eradication or control efforts would be successful, and the present distribution of the pest within the state. The ratings are not laws, but are policy guidelines that indicate the most appropriate action to take against a pest under general circumstances. Local conditions may dictate more stringent actions at the discretion of the CAC, and the rating may change as circumstances change.
The precise policy language is given below. This system has been in place since at least 1977, and revised in May 2009. The term "commissioners" refers to the County Agricultural Commissioners.
Action Oriented Rating System Purpose
To advise commissioners as to the Department's policy regarding any pest action.