Except as otherwise provided by Section 6173, in the interest of the public welfare and general prosperity of the state and to provide for the control, eradication, elimination, and prevention of endosepsis and other plant diseases, all caprifig trees used for shade, ornamental, or decorative purposes, and caprifig trees in, or associated with, any fig orchard which produces calimyrna or other Smyrna-type figs that aggregate in number more than one and one-half percent of the fig trees in the orchard, are unlawful and a public nuisance.