Oregon Revised Statutes Aviation § 837.085

(1) Unless a permit is granted by the Director of the Oregon Department of Aviation or except in an emergency, no person shall throw or drop any missile or other article or substance from any aircraft in flight, except over ground temporarily or permanently devoted to flying, or over open water.

(2) This section does not prohibit, or require a permit for, the use of an airplane for crop dusting or any other agricultural purposes or for seeding any agricultural or horticultural crop or for dusting or spraying in furtherance of insect and pest control. Any such use of an airplane shall be made with due regard for the safety of others.