Your UAS Does Not Have The Right-Of-Way
§ 107.37 Operation near aircraft; right-of-way rules.
(a) Each operator must maintain awareness so as to see and avoid other aircraft and vehicles and must yield the right-of-way to all aircraft, airborne vehicles, and launch and reentry vehicles.
(1) In order to maintain awareness so as to see other aircraft and vehicles, either the operator or a visual observer must, at each point of the small unmanned aircraft’s flight, satisfy the criteria specified in § 107.31.
(2) Yielding the right-of-way means that the small unmanned aircraft must give way to the aircraft or vehicle and may not pass over, under, or ahead of it unless well clear.
(b) No person may operate a small unmanned aircraft so close to another aircraft as to create a collision hazard.
This is simple. You can not interfere with another aircraft, and that includes another UAS. If the spray plane is nearby, you have to move, not him.