About 8-10 years ago we were sprayed by a crop duster plane while he was spraying the neighbor's fields. I was outside at the time, and saw the plane dumping spray as it went over our house which is in the middle of our property. Almost all our grass died, we lost many, many trees, and 2 horses and 2 dogs died...all with the same symptoms (open running sores, strange lumps and tumors, paw pads and hoof undersides sloughing off continuously, and liver failure). The pilot got really ugly with my dh, denied everything, and insisted he hadn't used anything harmful anyway. Dh asked him if he'd used a certain chemical (can't think of the name but it's like Agent Orange), and he flat out denied it and gave us the name of some other chemicals he'd supposedly used. We finally called our local extension agent who called the state ag. dept. They came out and tested our soil and trees and determined that we hadn't been oversprayed...we'd taken a direct hit. They also demanded the pilot's records which showed he'd lied to my dh...he did use the chemical dh had asked about. The state gave him a hefty fine.
We really aren't into sueing people so we let it go. If I had it to do over again, I would sue. The damage was much more severe and long lasting than we had originally thought. The pilot learned nothing and continues his sloppy practice even though he has been fined again. I've personally seen him overspray other people's trees and pastures...which WERE a considerable distance and across the road from where he was supposed to be spraying, and those people suffered damage also.
The only good thing that came out of our situation is that we talked to our neighbor (who had contracted with this jerk to have his fields sprayed) and told him if it happened again we would be sueing everyone involved. Since then he has sprayed using a truck and wagon, and sprays by hand along our fence line.
Arm yourself with plenty of good photos, get someone out from the state to test your soil/plants right after your neighbor sprays, and see your lawyer. You have more at risk than a few flowers. Those sprays are NASTY. Farmers have every right to farm their land. They also have an obligation to keep their chemicals on their own land.