Your Reading List

Stopping sprayer clean out errors

Curb those embarrassing mistakes with 
tips from sprayer pro Tom Wolf

Spraying machine working on the green field

When Tom Wolf told his audience at CropSphere in Saskatoon on January 9 that sprayer clean out errors can be embarrassing, the nervous laughter in the room made it clear that most farmers have made some sort sprayer mistake. And, as Wolf pointed out, making the crowd laugh again, those mistakes usually happens in the field near the highway.

Tom Wolf is a sprayer consultant with AgriMetrix and, along with a partner, runs the helpful website Sprayers101. At CropSphere, Wolf reminded us that, with more dicamba-tolerant soybeans in local fields, we’re going to be seeing more spray issues in the future. “If you think that canola is sensitive to Group 2 residues, multiply that by 100. That is how sensitive soybeans are to dicamba. So we have to be super diligent,” Wolf said.

The symptoms of dicamba damage are easily identifiable, even for people who don’t know a lot about farming. “It is of great concern to the industry as a whole because anyone can see a cupped leaf and say ‘oh oh, agriculture,’” Wolf said, meaning that urban residents may take a negative view of our farming practices.

The problems that farmers, primarily in the U.S., have experienced with dicamba in the last couple of years are “bigger than clean out” issues, Wolf says. However, to avoid crop damage (and embarrassment), careful sprayer clean out is a must.

Planning the clean out

You will know your in-field problem is a result of a spray clean out issue when the problem is a V-shape. “The classic is a sudden start with a V-shape petering out,” Wolf said. The contaminated spray reaches the closest nozzles first and the end nozzles last.

To avoid this problem, Wolf said, there are two steps: dilution and decontamination.

“The first step that we all must do is dilute the remainder in the tank.” The less you have in the tank when you’re finished spraying the field, the easier your clean out will be. “We cannot empty the tank completely, so there’s always going to be something left in the plumbing — a few gallons. And that must be diluted.”

“Once you have a clean plumbing system, then you decomtaminate.”

Wolf recommends identifying potential problems early. Pay particular attention to the damage Group 2 herbicides can cause in canola, and dicamba in soybeans. “Those are big ones.”

“If you have a situation where you’re going to be spraying your canola and you’re also going to be spraying a Group 2,” Wolf said, “try to spray the Group 2 after the canola.” Of course that won’t always be possible.

The last tank is the key to clean out. “That’s a very important tank.” Sometimes, there are extra steps you can take. For example, DuPont suggests adding ammonia to glyphosate in the last load of the day, to boost the pH. (DuPont’s website suggests adding 10 L of household ammonia containing three per cent ammonia to Express SG, prior to the addition of Express, water and glyphosate.)

“The other thing you want to do on your last tank?” Wolf asked. “Be really, really sure that it’s going to be empty when you’re done.” Or as close to empty as you can get it. There might be cases where you can spray double the label rate, to empty the tank in the field rather than in your yard.

Once you’re done spraying, Wolf says, “Clean it right away.”

Group 2 products

When it comes to sprayer clean out, all Group 2 herbicides are not equal. Wolf and his co-reserachers have divided Group 2 herbicides into four chemical subgroups. For products in three of these four categories, ammonia will raise the pH and help the solubility, but it’s not useful for herbicides in the fourth category.

1. Sulfonylureas. These include thifensulfuron (Refine) and tribenuron (Express) — Dow/DuPont products. These are the “classic Group 2 problem,” Wolf says. “They’re typically dry formulations and they typically dissolve better at higher pHs.”

2. Triazolopyrimidines. These include florasulam (PrePass) and pyroxsulam (Simplicity) — traditional Dow products. “Those are typically liquids, but they also dissolve better at higher pH.”

3. Triazolones. Such as Varro, Velocity and M3. These also dissolve better at higher pHs.

4. Imidazolinones. These include imazethpyr (Pursuit), imazamox (Odyssey, Solo), imazapyr (Ares) and imazamethabenz (Assert) — primarily BASF products.

There are known as the “imis.” Wolf said, “they dissolve better at low pH. And they are not implicated in our tank cleanout issues. They don’t even recommend ammonia as a tank cleaner.” “In fact,” Wolf said, “if you clean those with ammonia, you raise the pH, you’ve hampered their solubility. You go against what you should be doing.”

For farmers interested in taking it to the next step, Wolf recommends buying a pH meter for about $50.

What’s the ideal pH? “Most of our herbicides lower the pH below seven,” Wolf said. Glyphosate will typically lower the pH to five.

“You want to raise the pH back up to seven if you can. That’s what the ammonia is for.”

Oily mixtures

Oily tank mixtures, EC formulations, can make clean out problems worse. An EC formulation is an emulsifiable concentrate — typically a liquid active ingredient, petroleum-based solvents and an agent that forms an emulsion.

“An EC formulation is milky in solution,” Wolf said. This “milk” is “water plus two per cent oil in emulsion.” The oily layer in ECs can trap residue on sprayer walls. “If you do have an EC mixture in there, you need to use a detergent to get rid of that oil.”

Know your plumbing

“Understanding your sprayer’s plumbing is absolutely imperative,” Wolf said. He recommended climbing under the sprayer to figure out which hose is going where, and why. Sometimes, this can be a difficult job, but Wolf sees it as essential. Once you know where the herbicide is going, you can identify places (like boom ends) where residue is likely to accumulate.

Steel tanks are easier to clean, Wolf said, but they can be difficult to see, with baffles and false floors. “It just means you have to be diligent.”

For good sprayer clean out, Wolf believes a clean water tank is an essential sprayer component. If you don’t have one from the factory, he recommends retrofitting one.

Know what your dealing with

The effectiveness of your final rinses will depend on how much product you have left to dilute.

Once your pressure gauge has gone to zero, do you known how much product do you have left in your sprayer?

“If you spray a water-based solution that’s clear, and if you’re going to an EC that’s milky, here’s what you do. There’s milk in the tank, and your boom hasn’t seen any of that stuff yet. You start your stopwatch when you start your sprayer.” Also, reset your gallon count to zero. Then, “when your last nozzle sprays milky stop the sprayer, stop your stopwatch and check your gallons.” This way, you’ll know how much was in the tank when you started.

Wolf explained the power of serial dilution: If you have 50 gallons left in the tank and you use a 150 gallon flush, you have four-fold dilution (diluting 50 gallons into a total of 200 gallons). “That’s all that you’ve just accomplished and you’ve wasted 150 gallons of water,” Wolf said.

If instead you use that same amount of water for three 50-gallon flushes, you’ll have eight-fold dilution (two-fold x two x two). “That’s the same as a 350 gallon flush.”

If you’ve managed to only have 10 gallons remaining in the tank, a 350-gallon flush will give you 16-fold dilution. Three 50-gallon flushes would give you 216-fold dilution (eight-fold x eight x eight). “That’s the equivalent of diluting that 10-gallon remainder by 2,150 gallons.” Using four 35-gallon flushes would be even better.

Wolf had two key points: try to have a small volume remaining in the tank at the end of the field, and clean out with small batches of the same volume are better than using a single, large batch.

Sprayer design

Many of the problems with sprayer clean out could be improved with better sprayer design. Wolf believes European models are already more advanced than models available here. In the future, he says, “I think plumbing designs like continuous cleaning and recirculating booms really are going to make this job a lot easier.”


Wolf pointed out that “water that has enough residue to kill canola or soybeans looks exactly the same as clean water.”

Then he told a joke. “When do you know that you’re done cleaning your sprayer? In two weeks.”

However, when farmer Gerrid Gust posted this joke on Twitter after the meeting, we soon found out that residues can last even longer.

In the Crop Protection Lab, Saskatchewan’s provincial weed control specialist Clark Brenzil has seen several plants that have suffered from herbicide injury.

Based on sprayer history and field patterns reported by the farmers bringing those plants in, Brenzil has come to a worrying conclusion. “We’ve got cases that have been sent to us where there has been no Group 2 in the sprayer going back to the burn-off. That’s the only place where the Group 2 was in the sprayer.”

About the author

Leeann Minogue's recent articles



Stories from our other publications