Trace amounts of herbicide left in the sprayer can injure a crop when the sprayer is used again, according to Rich Zollinger, a weed specialist with North Dakota State University.
“A gallon or two left on the bottom of the tank doesn’t seem like much but it can seriously damage a crop, depending on the herbicide used.”
Herbicides applied at low concentrations can cause the most damage. They include all Group 2 ALS inhibitor mode of action products and hormone-type herbicides such as 2,4-D, MCP and dicamba.
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“Even one percent of the recommended rate of these herbicides will definitely cause damage to many broadleaf crops,” Zollinger said.
“The damage to legumes caused by trace amounts of ALS herbicides in the spray is greater in the presence of grass-selective herbicides.”
Immediately after using either ALS or hormone herbicides, the sprayer should be thoroughly cleaned using the appropriate method. Sprayer cleanout procedures are given on many herbicide labels and the procedure on the label should be followed for specific herbicides.
The following sprayer clean-up procedure is effective for most herbicides:
- Drain the tank and thoroughly rinse the interior surface with clean water. Spray rinse water through the spray boom for at least five minutes.
- Fill the sprayer tank with clean water and add a cleaning solution. Many labels provide recommended cleaning solutions. Fill the boom, hoses, and nozzles and allow the agitator to operate for 15 minutes.
- Allow the sprayer to sit for eight hours while full of cleaning solution so the herbicide can be fully desorbed from the residues inside the sprayer.
- Spray cleaning solution through the booms.
- Clean nozzles, screens and filters. Rinse the sprayer to remove cleaning solution and spray rinsate through the booms.
Chlorine bleach, ammonia, and commercially formulated tank cleaners are common types of cleaning solutions. Chlorine lowers the pH of the solution, which speeds the degradation of some herbicides. Ammonia increases the pH of the solution, which increases the solubility of sulfonylureas and weak acid herbicides. Commercially formulated tank cleaners generally raise pH and act as detergents to remove herbicides.
Never mix chlorine bleach and ammonia because a dangerous and irritating gas will be released.
“Sprayers should be cleaned as soon as possible after use to prevent the deposit of dried spray residues,” Zollinger said.
A sprayer should not remain empty overnight without cleaning.
