Sprayer cleanout is important. Many of the herbicides commonly used today are active at very low rates, often ounces/per acre or in some cases, a fraction of an ounce per acre. A very small residual amount of these types of herbicides left in the sprayer has the potential to cause some significant damage if the next crop sprayed is sensitive to the herbicide. Depending upon the herbicide used, the label may require an adjuvant such as a surfactant or a crop oil to help the product perform better. While the effectiveness of the product is increased, those adjuvants can, in some cases, dislodge or break down herbicide residues that were stable and/or embedded in tank walls, hoses or screens. Those residues end up in the current spray solution and have the potential to injure a sensitive crop.
Thorough sprayer cleanout requires understanding how much spray solution remains in your sprayer after the application is over, recognizing where pesticide residues can accumulate, and following a cleanout protocol or checklist. Many spray tanks do not drain completely, so even when you can no longer pump a spray solution, there is residual in the tank. Often the spray tank drainage opening is slightly above the bottom of the sump. It is good to know the size of the sump and the area below the drain opening to determine how much spray solution remains in the tank after “empty”. When the tank is empty and the pump has lost its prime spray solution still remains in the booms. According to the Purdue Extension publication entitled “Removing Herbicide Residues from Agricultural Application Equipment” a 120 foot boom can hold 35 gallons of liquid, a 90 foot boom 25 gallons and an 80 foot boom 18 gallons. Even if you operate a much smaller sprayer there can be several gallons of spray solution left in the boom after the spray tank is empty. Finally, look at the hoses on your sprayer. Any place where hoses sag can potentially be a place to trap liquids.
Herbicide residues can accumulate in both obvious and some not-so-obvious locations. Obviously, the spray tank, hoses and screens are places where herbicide residues can accumulate. As fiberglass and poly tanks age, they can develop micro cracks and roughened surfaces that provide places for herbicide residues to accumulate and that make thorough cleaning more difficult. Hoses, and in particular rubber hoses, can hold herbicide residues, especially as they age and develop small cracks and rough edges. There are some non-porous hose materials including plastic coated hoses and nylon braided hoses that prevent herbicide residue accumulation. They are costly, but for the operator that sprays a lot of acres or switches back and forth often between crops, the extra cost may be worth it. Screens are designed to catch materials that could potentially plug a nozzle and offer another place herbicide residues accumulate, in particular dry formulation types of herbicides.
Less obvious places where herbicide residues can accumulate include unused nozzle clusters, nozzle turrets, valves with “Y” junctures, flow meters, and the sight gauge tube and end caps. Pay special attention to end caps. Depending upon the sprayer, the last nozzle or nozzle body on the boom may be several inches away from the end cap. The dead space between the last nozzle and the end cap is a prime site for herbicide residues to accumulate.
In the Purdue publication mentioned previously, a recommended protocol for sprayer cleanout includes the following steps and involves three rinses that each use ten percent of the tank’s capacity per rinse or three times the spray volume applied per acre:
- Empty the boom at the end of every spray day
- First rinse: applied in the field or fallow area and water coming out of nozzles should be free of any tint or sheen.
- Remove and clean screens. Flushing water through screens is not cleaning screens. The best way to clean screens is to remove them and scrub the screen from the inside out using a brush and soapy water combined and then rinsed with pressurized water.
- Remove and clean end caps. In some cases, it may be necessary to insert a brush and scrub the inside, that dead area space. Flush the line with water and flush water through nozzles. Rotate all the nozzles on a turret and flush out.
- Second rinse: Put end caps back on and circulate water through hoses, pumps, tanks, fill lines, and flow meters. Turn on each boom section and flush separately.
- Add tank cleaner and circulate throughout the pump and all sprayer plumbing. Labels for tank cleaners are usually not specific in terms of how long to hold the cleaner in the sprayer, but in general, the longer you can leave the cleaner in the better it works.
- Add water and flush out tank cleaner
- Final rinse and flush.