A crop duster is flying directly over my house while spraying. I can see the mist coming out while I am standing in the middle of my yard (6 acres). Is this legal?
No. 14 CFR 137.37 - Manner of dispensing is pretty clear:
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.
Flying directly over you or your house while spraying is illegal. There are factors like altitude etc, but spraying pesticides over people is rarely legal.