Spray good for one, not good for other

The ‘ticking time bomb’ | Crops, particularly canola, can be damaged by residue of other herbicides left in the sprayer

More awareness of the potential for carryover during crop spraying could result in fewer injured canola crops, says a weed control specialist.

Clark Brenzil of Saskatchewan Agriculture said an increasing number of cases have come through the Crop Protection Lab in Regina in which producers apply one herbicide and see injury symptoms from another.

The lab says that sprayer contamination caused all of the cases last year.

“The key sign about tank contamination is when you’ve got injury that runs in a straight line, and only equipment runs in a straight line,” he said during an integrated canola pest panel discussion at CropSphere in Saskatoon Jan. 14.

Sprayer contamination becomes a bigger problem in diversified cropping systems with different sensitivities to different groups of herbicides.

“That means that we have to be really on the ball about making sure our sprayers are cleaned out when we go from one crop to the next,” Brenzil said.

Contamination occurs when herbicide deposits form in the sprayer, whether in the tank, screens, nozzles or the overall plumbing during previous applications.

“There may be successive layers that build up over time. It may be even two or three crops beyond the one that you’re treating is the one that ends up showing injury, but it tends to be in crops that are very sensitive to herbicide injury,” he said.

“That’s a ticking time bomb for when you get one of those cleaning type herbicides or adjuvants that come into the system and flush all that stuff out and injure the crop.”

Most lab cases in the past five years have involved Liberty applied to 
LibertyLink canola. The adjuvants in Liberty are soapy and act as detergents in the tank, which break down fatty substances.

Other herbicide applications involving solvent based adjuvants, such as Merge or Turbocharge, can also clean fatty substances out of the tank.


Brenzil said a Group 2 herbicide is the contaminant herbicide in most cases, but it isn’t what necessarily causes the deposit. That usually occurs when it is applied in association with something with an oil or fat based adjuvant. The fat can layer over the Group 2 herbicide and trap it in the sprayer’s plumbing.

Damage can also occur several loads after the contaminant herbicide was applied.

“Canola is probably one of the most susceptible crops to Group 2 injury, so you’ve got the perfect storm occurring when you’re applying to LibertyLink canola,” he said.

A common assumption is that multiple tanks of another herbicide that isn’t a contaminant type will clean enough of the problem herbicide out of the tank so that no cleaning is necessary before going into a sensitive crop.

“That’s not necessarily the case,” he said.

Brenzil said he saw a scenario last year in which several tanks showed no injury and then one tank “completely obliterates the canola in that area and then subsequent tanks are fine.” It was the first time he had ever seen that occur.

Lab tests determined that the tank load that caused the injury had sat for a significant time with Liberty inside the sprayer.

“It’s got more time to do more cleaning and so it pulls out a very concentrated amount of that contaminant herbicide and goes out on the field and it completely kills the canola,” he said.

The late start to seeding and variable weather combined to cause significant problems last year. As a result there were sporadic periods when sprayers operated for a day or two and then sat for two or three days.

“That’s not only going to contribute to more layering on the front end of the contaminant but it’s also going to contribute to those really catastrophic removal events where you get complete death to that one tank load.”


Brenzil said many farmers also assume that spraying glyphosate will alleviate the problem.

“There’s an assumption out there that glyphosate will clean things out of tanks after you’ve got Group 2 combination ahead of time,” he said.

Brenzil said the new glyphosate formulations are oily and easily layer on tanks. This may coat more fat over the top of the contaminant and trap it even more.

Prepass and Priority products also stood out last year as some of the primary contaminant sources by forming solids and settling.

Good sprayer sanitation is the key. Brenzil said the sprayer needs to be cleaned out with at least water but preferably a full cleanout after any prolonged period of inactivity.

“Don’t let that stuff sit in the tank and layer things on the inside of the sprayer,” he said.

As a short-term solution during the summer, Brenzil advised letting water sit in the tank after it’s been emptied and cleaned before resuming spraying.

Using an ammonium based cleaner is recommended for Group 2, but it is not a strong enough grease cutter.

“Don’t be afraid to add detergent into that ammonia rinse or even use one of the commercial tank cleaners that have both of those as a component,” he said.

“The detergent breaks down the oil, the ammonia solubilizes the Group 2 and they all go out in the rinse.”


For more information, contact the Agriculture Knowledge Centre at 866-457-2377.

  • 85% overall on the article. Just a couple of points of clarification;
    1) PrePass and Priority are only a particular problem for settling out of solution if they are mixed with the wrong glyphosate formulations.
    2) The key to preventing a problem is to be sure to clean out the sprayer each time the sprayer is stopped for long enough for the power plant to be turned off or clean your sprayer as often as you shower. Start the cleanout in the evening and let the cleaning solution sit in the sprayer overnight to work on caked on layers.