Some permies might not have been around in the 80s with the medfly scare in California, but this video shows that Big Ag will stop at nothing to keep mono-cropping alive. If you locate your homestead among fields of monocrops or in a state that gets lots of income from monocropping, beware of the "threat from the skies."
NY Times Video: Battle over the Medfly 1981
(Note: not sure which is more scary, the aerial spraying or the hair and clothing styles we wore back then, argh!)