Consider the use of drift retardant adjuvants. Read the label for any advice it may have on the use of adjuvants. Larger spray droplets have a lower potential for drift. Larger nozzle orifices and lower pressures promote larger droplet sizes. Applications made as close to the target as possible also reduce the possibility for drift.
Excessive winds are an obvious cause of drift problems.
Backflow Prevention for Chemigation Idaho's chemigation law requires antipollution devices to prevent backflow into the water source when adding chemicals through the irrigation system. A chemical injection line check valve is needed. An interlock is needed to shut off the chemical injection when the water supply fails. In addition a combination air and vacuum relief valve is required. A gooseneck pipe loop is an alternative.