Presumption that owner and occupier permitted growing of prohibited plants
18.  If any prohibited plant is found growing on any land in contravention of any order made under section 17, the owner and the occupier of the land shall be deemed to have permitted the plant to grow unless the owner or the occupier, as the case may be, proves —
(a)that the plant was planted without his knowledge and consent; and
(b)that on becoming aware of the existence of the plant he forthwith effectually eradicated and destroyed it.