CA Food & Agric Code Section 5781

If the director determines that a particular pest, either within the state or from any area which is adjacent to the state, cannot be eradicated or effectively controlled by recognized ordinary means, or that it is impracticable to eradicate or control the pest without the destruction, in whole or in part, of uninfected or uninfested host plants, the director may adopt regulations which do all of the following:

(a)

Declares a host-free period or a host-free district, or both.

(b)

Describes any host and the district in which the planting, growing, cultivating, or maintenance in any manner of any plant which is capable of continuing the particular pest is prohibited during a specified period of time and until the menace from it no longer exists.