It is illegal to spray pesticides from an aircraft without an appropriate Environment Protection Authority licence.
Spraying pesticide from an aircraft also has strict controls in place, such as spraying within 150 m of a residence, school or other public place requires written consent of the occupier. There are some exceptions, such as roads.
Pesticides sprayed from aircraft are subject to drifting into untargeted areas. Issues with spray drift need to be carefully managed.