Googling, maybe as you did, seems to show as many answers to the "who owns the airspace...." question as there are people to answer it. Hard to define. Probably even varies by state laws. For drone work, I have read that a landowner controls (not owns) the airspace up to the tallest structure on their property. That's one of the 500 possibilities found when searching for airspace rights and ownership.

Re. getting a lawyer, I'd say one would have to have specific damages to involve the court. But, once you get involved in legal action, you probably put yourself in a situation where you may lose some friends. If you don't care, go for it. If there was deep economic damage, go for it. But the legal action will go against the applicator and pilot. If the pilot is hired, he'll tell company he doesn't care to ever go back to that field, even though it isn't the field owner's fault. The field owner may also get drug into it if the lawyer decides to throw mud up against the wall with everyone's name. The spray company may tell the customer, "it's not worth the money spraying your fields...not your fault, but I think we'll pass next time on spraying for you." So, then it will be neighbor vs neighbor. Not sure that's what everyone wants.

Sometimes, even though you may feel you're 100% right, the outcome may not be worth what you started out to prove.

Personally, I'd call the other farmer first, explain about the livestock, and ask him if he would call the applicator, or if he would mind if you would call & express your concerns.

Maybe it's different "there" vs "here", but whenever you mention getting a lawyer, you suddenly lose some friends, or at least have people that now keep you at arms length. Not sure that's everyone's goal.