How dangerous is it for a huge all black helicopter to be flying below 500 feet over my house, for a half hour now, spraying pesticides all over the area and my farm animals. It is shaking the whole house and almost took the tops off the tall trees in back.
The Federal Aviation Administration (FAA) has regulatory and safety oversight for Agricultural Operations (Crop dusting, pesticide spraying, etc., from aircraft). Agricultural Operators are required to be certificated by the FAA and their operations are subject to the Federal Aviation Regulations.
The Federal Aviation Regulation that addresses Agricultural Aircraft Operations is 14 CFR Part 137. This LINK is to Section 137.37 of that regulation and states the following:
137.37 Manner of Dispensing
No persons may dispense, or cause to be dispensed, from an aircraft, any material or substance in a manner that creates a hazard to persons or property on the surface.
If you think that this helicopter is spraying pesticides contrary to the regulation noted above, you may want to contact the local "Flight Standards District Office" (known as a FSDO) that is responsible for the area. Since the FSDO has regulatory oversight responsibilities for the Agricultural Operators in their area, this would be a place to seek some assistance.
Your question has many potential variables, so contacting the FSDO and explaining what you are experiencing may be the best method of reaching an answer to your question.
The phone number for the Lincoln, NE FSDO is (402) 475-1738 (from their website). I think Nebraska only has one FSDO.