Dicamba herbicides don’t leave much room for error. “A pop can [12 ounces] of leftover dicamba spray solution left in a 1,000-gallon tank is enough to curl up sensitive soybeans [spraying 10 gallons per acre],” says Vince Davis, a BASF technical representative. “Just 3 ml [6⁄10 of a teaspoon] of raw dicamba product in 1,000 gallon[s] is enough to contaminate a load.”
Proper cleaning of sprayers and avoiding tank contamination is important regardless of pesticide. However, the EPA addressed the importance of sprayer cleanout to avoid cross contamination as it revised the 2018 labels for Engenia, FeXapan and XtendiMax, the only dicamba herbicides legal to use in dicamba-tolerant soybeans and cotton.
“The new labels require applicators to document how and when they cleaned the spraye--before and after application. That information must be kept with your spray records,” Davis says.
Careful Sprayer Cleaning. The new labels generally require a standard triple-rinse (see “Triple-Rinse Regime,” above) sprayer cleanout with commercial-based detergent cleaner designed for the task.
One specific concern about dicamba is it requires more effort and care to be removed from the tank than some other commonly used herbicides, University of Missouri weed scientist Mandy Bish notes. “Some herbicides, such as glyphosate, can effectively dissolve remnant dicamba left in the sprayer following improper cleanout.”
Cleaning out residues before a dicamba application can be equally as important--a smidgen of ammonium sulfate left from a prior glyphosate tank mix can be enough to increase volatility of new formulations.
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How Clean? Tom Wolf, a sprayer consultant(sprayers101.com), recommends dividing the cleaning operation into dilution and decontamination.
“Doing the math so there’s little remainder in the tank makes dilution easier and faster,” he advises. Even a sprayer that is sprayed out isn’t really empty. The tank sump and recirculation hoses must still be diluted.
He recommends an app (agrimetrixapps.com/dilutionCalculator) to calculate how much dilution is needed. “In short, triple is better than double, quadruple is better than triple for any one total clean water volume,” Wolf explains. “You want to do it enough to reduce the herbicide concentration well below the danger threshold.”
Decontaminate Next. There are all kinds of hiding places for the active ingredient, as well as sediment and residue. Chief offenders are strainers, screens and end caps. A Mississippi State University study used electron microscopy scans to show how checked and cracked hoses can harbor dicamba. It found polyethylene hoses may help ensure a more thorough dicamba cleanout.
Some applicators have gone to dedicated sprayers and handling systems to reduce risk, Davis says. “Anything that formulated product and/or spray-solution touches prior to the sprayer is a potential source of contamination. Nurse tanks, shuttles, mixing and loading equipment, hoses and pumps at the shed and in the field are other things that need to be considered.”
• Spray out booms every night.
• Perform first rinse in the field.
• Remove, clean and replace all screens.
• Remove and clean end caps.
• Add and hold commercial tank cleaner.
• Perform third rinse and flush.
• Properly dispose of rinse water.
Source: Fred Whitford, Purdue University (For more specifics, download the “Removing Herbicide Residues From Agricultural Application Equipment” bulletin at bit.ly/2FUjRLg.)
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