Top Crop Manager

Maintenance Seed & Chemical
Clean out the sprayer tank!

Procedures and diligence are required to do the job thoroughly every time.

November 19, 2007  By Lorne McClinton

87aSpraying season is a busy time. Farmers have a lot of acres that need to be sprayed in a narrow window before weed pressure robs crop yield. With today’s diversified crop rotations, farmers know they have to properly clean out their sprayers before switching crops, but cleaning a sprayer properly is easier said than done. Every year, tank cleanout issues kill or badly damage a few crops, and sometimes border on the strange.

“Every year I get mysterious calls from applicators about tank cleanout problems,” says Tom Wolf, a researcher with Agriculture and Agri-Food Canada in Saskatoon. “Calls like this: ‘I sprayed Refine Extra last year. This spring, I sprayed six tanks of glyphosate for pre-seed burnoff. Later I sprayed my Liberty Link canola, and the Refine Extra residue killed it’.”

Is this possible? How can material remain active in the system after six tanks of another product?


“The answer is, ‘it is difficult to say’. We’ve tried, but we haven’t been able to replicate this in our research. First, we have to make sure that the issue is in fact tank cleanout. We need to make sure it’s not soil residue, or some other cause.”

Tank cleanout issues leave tell-tale signs. The first sign is found where the first tank applied in the field shows the worst crop damage, and the damage decreases as more and more spray solution is put through the sprayer. For example, damage may be severe where the first tank was sprayed, and improves dramatically with the second tank.

“The second tell-tale sign is if damage is significantly worse at the beginning of the first pass you make, after the sprayer has sat for 10 minutes or an hour,” Wolf says. “You may see significant damage that diminishes with distance. The third tell-tale sign is the characteristic ‘V’ shaped pattern of damage caused by a contaminated boom being flushed clean. If you have any of these three symptoms, it is probably a tank cleanout problem.”

Wolf says diagnosis of the problem is helped if there is a sprayer miss. The crop in the untreated area can be compared to the sprayed crop to help determine if it is a crop safety issue.

Thoroughness is key to tank cleanout

Wolf says thoroughness and diligence will solve 95 percent of tank cleanout problems. He has developed a five-part set of cleaning instructions to help producers fine-tune their procedures.

“Start by doing a visual inspection,” Wolf says. “Residue might precipitate out and accumulate in sumps or in corners of the boom. So a thorough visual inspection will help identify where the problem areas might be. After this we go through the components starting with the tank.”

The best way to clean the tank is to use a garden hose and a reasonably high-pressure gun to direct-spray the tank with a clean water source. With this method, a tank can be cleaned with as little as 10 gallons of water. Wash down nozzles as well.

The second area to clean is the sump. Poorly designed sprayer sumps are one of Wolf’s pet peeves. “You can’t completely drain the sump in most sprayers. The best you can do is to leave a couple gallons of water in the bottom, add more water to dilute it, and then do it again and again. It is a very cumbersome process.”

The third thing to pay attention to is the plumbing. One and two inch plumbing lines provide a large reservoir for residual herbicides. All lines need to be flushed. Use clean water in the tank and pump it through the boom. “Make sure you open and close the various agitation return lines,” Wolf says. “Be thorough, and make sure that all the lines receive fresh water. It sounds easy but in practice it is difficult. If you start with 100 gallons of fresh water in your tank, and then start up the pump, the first thing that happens is all the pesticide that is in your suction and return lines comes right back in your tank and contaminates your cleaning solution. This means the only way to ensure your lines are clean is to flush them over and over again.”

The filters require special attention, especially when using sulfonylureas (SUs) like Refine Extra. Their dry flowable clay-based formulations can remain caught in the sprayer’s screens even after a fresh water flush.

“This is a common problem,” Wolf says. “If you clean your tanks but not the filters, then every time you stop, a little bit of chemical comes out of the clay and goes into solution. When you start up again, you get a shot of high concentration chemical that diminishes in time. So take out your screens, visually inspect them and clean them thoroughly.”

Tank-cleaning adjuvants

Ammonia can be very effective when cleaning a sprayer after using a SU. Ammonia does not deactivate herbicides. It works by raising the pH, which helps SUs dissolve.

“While I recommend ammonia, and any ammonia containing adjuvant for decontaminating your sprayer, you still have to be thorough,” Wolf says. “You can’t be sloppy, even with ammonia.”

Often, SUs are tank-mixed with an emulsifiable concentrate (EC) like Horizon or Puma Super. Since these EC products are oil-based they can leave an oily film in the sprayer, which can trap an SU.

Wolf recommends using a soap-like surfactant to remove the oil. “Syngenta recommends using Agral 90, a non-ionic surfactant, to clean some of its products. It is basically a detergent.” However, Wolf emphasizes that not every surfactant is a good tank cleaner. “There are certainly a lot of products out there that are also oil-based. They may be good surfactants, but they are not good cleaners.”

Fill and flush sprayers in the field

“We are trying to encourage people to fill and to decontaminate their sprayers in the field, not in their yard,” Wolf says. “There are all kinds of important water sources in the yard that you do not want to contaminate. I think sprayer decontamination is one of the industry’s skeletons in the closet. I don’t think we have addressed the issue too well. I think we would rather not know what farmers do, than address it head on.”

He also believes it should be possible to build sprayers to make the job of decontamination easier. “I would like cleaning a sprayer to be so simple that when you are done spraying, all you need to do is hit a decontamination button in the cab. The technology exists.” What is needed is a reservoir of clean water, and a series of remote control valves that will open and close to flush out the appropriate part of the sprayer in sequence to finish the job. “It should take five minutes and you should never need to leave the cab, or come in contact with the spray. I don’t know why we haven’t done it.”

The Bottom Line

Very few farmers can say they have never seen crop damage from sprayer contamination in their own fields, although they might like to describe the neighbours’ errors before their own. However, I hope once burned, twice shy! Because of the increased mix of crops and chemicals, the potential for crop damage increases. It is definitely a ‘must’. Farmers have to take the time and spend the small amount of money to buy proper surfactants to clean out the sprayer diligently. It is so true that thoroughness is the key to tank cleanout.  – Ian McPhadden, Milden, Sask.

This is a very important topic. I have seen fields with major injury from residual chemical from not having a thorough cleaning of the sprayer. I personally have had some of these problems when changing over to sensitive crops like peas. I really like the idea of being able to clean the sprayer from the cab. This could solve the rinse problem. It would also be helpful to have a list of cleaning adjuvants as well as surfactants which work best with each chemical. I have used Merge and ammonia at different times to ensure that the sprayer is completely clean. – Dave Hegland, Wembley, Alta.


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