Most non air inducted flat fan nozzles suck in the wind. I remember one of my friends running a herbicide trial. He had one of those 9' booms with the nozzles spaced at 10". They were conventional flat fans. He was applying a combination of Celsius and Monument. As it was blowing about 10 MPH with shifts in direction and gusts, I was worried about the trees down wind. If the trees were killed or damaged, that is chemical trespass. I consider conventional flat fans unusable for herbicides except in perfectly still conditions. In my location that is a rare event and those perfectly still conditions are normally accompanied by weather conducive to inversion or volatility.
They who can give up essential liberty to obtain a little temporary safety, deserve neither liberty nor safety.
Benjamin Franklin 1775
Sell not virtue to purchase wealth, nor Liberty to purchase power.
Benjamin Franklin Poor Richard's Almanac1738