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 are 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 the owner’s or the occupier’s knowledge and consent; and
(b)that on becoming aware of the existence of the plant the owner or the occupier forthwith effectually eradicated and destroyed it.