How much water should you flush through sprayers in the field? “A general rule of thumb is to use 10% of the tank’s capacity per rinse," writes Fred Whitford and his co-authors in Removing Herbicide Residues from Agricultural Application Equipment - How Proper Cleaning Helps Prevent Crop Damage and Improves Performance, a publication of Purdue University Pesticide Programs.
Another general rule says to add at least two to three times the amount of gallons applied per acre. Each rinse of the boom will range from 30-50 gallons of water. For example, if a spray application used 15 gallons per acre, 30-50 gallons should be sufficient to flush the sprayer. Add more water if the spray coming out of the nozzles during the flush process doesn’t look clean.
Some applicators drain as much product as possible out of tanks before circulating clean water. They will open the main valves to drain the tanks and hoses. They will put in 3 to 5 gallons of clean water and recirculate to get the remaining material out of the tank by reopening the tank valve. This tactic will make the first rinse a cleaner rinse, because the water is circulated between pump and tank.
Preliminary research suggests that rinsing three times with adequate water is more important than the type of detergent used for a commercial tank cleaner on the second rinse. Only use a cleaner recommended by the label and/or manufacturer.
The only absolute way to avoid tank contamination with plant growth regulators (PGR) is to have a sprayer dedicated to PGR applications. If this is not an option, a thorough cleaning for the required time with the proper tank cleaner and adequate water is crucial. Never mix ammonia and chlorine beach; their solution will produce a toxic chloramine gas, which is a health hazard to the applicator.
Have a plan to eliminate PGR residues from tender or nurse trucks as well. There have been examples where “hot loads” from an uncleaned nurse tank were supplied to the field sprayer, contaminating a clean sprayer. Outside sources of contamination also can come from shuttles and minibulks (not recommended to be reused), induction cones, tank-fill hoses, tires on sprayers with front mount booms and nurse tanks supplying hot loads.