Washington Revised Code Title 70. Public Health and Safety § 70.104.020. “Pesticide” defined

(1) Any substance or mixture of substances intended to prevent, destroy, control, repel, or mitigate any insect, rodent, nematode, snail, slug, fungus, weed and any other form of plant or animal life or virus, except virus on or in a living human being or other animal, which is normally considered to be a pest or which the director of agriculture may declare to be a pest; or

(2) Any substance or mixture of substances intended to be used as a plant regulator, defoliant or desiccant; or

(3) Any spray adjuvant, such as a wetting agent, spreading agent, deposit builder, adhesive, emulsifying agent, deflocculating agent, water modifier, or similar agent with or without toxic properties of its own intended to be used with any other pesticide as an aid to the application or effect thereof, and sold in a package or container separate from that of the pesticide with which it is to be used; or

(4) Any fungicide, rodenticide, herbicide, insecticide, and nematocide.