Everyone says quality is important, but it is easy to cut corners when we’re pressed for time. Using contaminated sprayer tanks seldom ends happily, though. Saving a few minutes by taking shortcuts during the herbicide cleanout process almost guarantees you will spend more time in the long run resolving contamination issues. It is much smarter to spend the time to do it right the first time.
Even very small amounts of herbicide residue left in tanks, hoses, screens, fittings or booms can seriously damage crops. There is no place to hide when the wrong herbicide shows up on a crop.
Properly cleaning a self-propelled or pull-behind sprayer may take an hour or more. If you cut corners, you increase the probability that the next field you spray may exhibit an unwanted result. By following specific procedures step by step, you can clean the system each time so you can safely treat subsequent crops with an herbicide.
Step 1: Spray Out Booms Every Night
When applicators leave herbicides overnight in rubber hoses, the herbicide can penetrate and reside in the hoses, becoming more difficult to remove. Some products can settle out in as little as 45 minutes if they are not agitated. Leaving sprayers idle allows herbicides to penetrate into the linings of the hoses or tanks. It also allows time for residue to settle out and become more cemented to interior surfaces.
Completely empty any herbicide left over in the sprayer while in the field. Second, add 10 times the sump’s remnant of clean water, circulate and spray it out in the field. Repeat. These two rinsing steps will take care of the majority of the cleaning and won’t take very long.
End each day by cleaning or emptying the booms, followed by a flush of water to help reduce the risk that herbicides will penetrate hoses.
Step 2: Perform First Rinse in the Field
During the first rinse, water coming out of the nozzles needs to pass the eye test; water should be clear without any evidence of a tint or sheen.
A good rule of thumb is to use 10 percent of the tank’s capacity per rinse. 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 to 50 gallons of water. Add more water if the spray coming out of the nozzles during the flush process doesn’t look clean (e.g., milky-looking).
Some applicators drain as much product as possible out of tanks before circulating clean water. This makes the first rinse a cleaner rinse, because the water is circulated between pump and tank.
You should spray the first rinse over the last crop you treated. Research from Colorado State University evaluated sequential spray tank rinses and found that the first rinse contained nearly the same herbicide concentration as the original solution.
The best-case scenario is to perform the second and third rinses (Steps 5 and 7) in the application field away from any ditches, streams and other water sources. If you choose to perform the second and third rinses elsewhere, take care to avoid contaminating any water sources. Growers should check with their respective state departments of agriculture to ensure this is allowed in their state.
Step 3: Remove and Clean All Screens
After performing the first rinse in the field, it’s time to remove the concentrated herbicide from sprayer equipment screens. Most of this is usually a pasty material that did not completely dissolve when it was added to the tank or that settled out of solution during the spray operation. This material will remain trapped in the screens until the next chemical is added or a solvent breaks down the herbicide residue.
Screens also capture grit, debris and even the occasional aluminum foil cap liners from containers. It’s important to clean off all these materials before the next application.
It is important to actually remove and clean all screens; never just flush them. No amount of water flushed through the screens will remove large particles that have become lodged in the wire and coat the mesh. The best way to clean screens is to scrub the screen inside-out with a brush and soapy water to loosen particles. Then, rinse the screens with clean water.
Step 4: Remove and Clean Boom End Caps
In many cases, there is about a 2-inch section of boom that extends beyond the last nozzle. Just like screens, you need to remove and clean these end caps before using spray equipment again. To clean the boom section of your equipment, first remove the end caps and scrape away any debris and residue inside them with a brush, tank cleaner or detergent, and water.
After thoroughly cleaning the end caps, replace one on each section of the boom. When you replace the end caps, it will probably be necessary to replace the O-rings because they are easily damaged.
Step 5: Perform Second Rinse with Water
A second rinse of water will dislodge most, if not all, of the loose residue that remains on the tank walls, lines the hoses, or is trapped in low-lying places. Circulate the water through the hoses, pumps, tanks, fill lines and flow meter lines.
Turn on each boom section separately to flush out the water in each. Once you’ve flushed all the sections, replace the end caps and remove the caps on the opposite side of the boom section. Continue to run water through the boom, section by section. After you’ve rinsed the boom sections, replace and tighten all end caps.
If your sprayer does not have end caps or quick couplers mounted on the boom or boom sections, leave the end nozzle out of each section, or consider installing a valve or quick coupler device to help with future cleanouts.
Step 6: Add Tank Cleaner
Tank cleaners are sophisticated products that break down the herbicide molecule, increase the herbicide’s solubility, and remove any residues that may have penetrated into the walls of hoses, tanks or fittings. However, tank cleaners have limitations. Remember that tank cleaners only work on herbicides that are vulnerable to alkaline hydrolysis. And never forget that tank cleaners are no substitute for a thorough cleaning.
Step 7: Perform Final Rinse and Flush
Some operators perform one last flush of water to ensure the system is as clean as possible. Others even go an extra step by removing the screens again and using a pressure washer to clean residues from the sprayer surface. Still others use a tank mix surfactant or fertilizer additive, which are good at removing herbicide residue that commercial cleaners can leave behind.
This article is excerpted from a Purdue University Extension report titled “Removing Herbicide Residues from Agricultural Application Equipment,” authored by several experts from around the country, including Fred Whitford, director of Purdue’s pesticide programs, and Kirk Foreman, commercial certified applicator with Falmouth Farm Supply in Falmouth, Ind. The full report can be accessed here.