Two more reasons to consider a jar test before tank mixing

It’s better to be safe than sorry when you combine multiple modes of action or include micronutrients in the tank

When tank mixing goes well, farmers can reduce the number of passes through their fields, saving equipment operating time and man-hours, reducing compaction and optimizing application timing. When tank mixing goes badly, however, the results can be disastrous. Because chemical companies won’t and, in fact, can’t test their products with every possible mixing option, making sure the intended mix is safe and effective is up to individual farmers.

Jar tests have never been more important due to tank mixes of three or even four modes of action for a single pass solution, or the inclusion of the newer category of micronutrients.

Of 2,000 farmers watching 50 hands-on jar test demonstrations, 75 per cent reported they were familiar with the concept and only 10 per cent said they’d conducted a jar test themselves. Spray experts say jar tests can save you money, time and frustration.

“Just imagine how many permutations there are — which chemicals, with which mixes, in what order, with what water, on what crop? It’s impossible for any company to do that,” says Jason Deveau, an application technology specialist with Ontario Ministry of Agricultural Food and Rural Affairs (OMAFRA) and co-curator of sprayer resource

If you’ve done your homework of reading the label, checking with the Pest Management Regulatory Agency and talking to a chemical rep or crop consultant and you still don’t have good answers on whether you can mix the products you’d like, your next step is to do a jar test. It’s just what it sounds like — a miniature replication of your tank mix inside a mason jar.

“If you’ve exhausted all the other avenues and nothing tells you that you can’t or shouldn’t, that’s when you jar test,” says Deveau. “Jar testing is a much better option than crossing your fingers and mixing 1,200 gallons. Obviously, you don’t want your sprayer to become a test tube.”

Presently, two factors make jar tests more important than ever. The first is the increasing concern about herbicide resistance. To delay the onset of resistance, weed management experts are recommending farmers mix multiple modes of action into single tanks.

“We’re not just mixing one or two but we’re into three and four modes of action for a single pass solution,” says Tom Wolf, sprayer expert and scientist and partner in Saskatoon-based Agrimetrix Research and Training, which specializes in the study of agricultural sprays.

Increasing the number of chemicals in a single tank mix increases the likelihood of negative interaction between two or more of the chemicals. In certain cases, unexpected interactions in a multi-product mix can occur even when any two of the included chemicals would be fine together. And, in some cases, incorrect mixing order can have disastrous consequences.

Another factor increasing the importance of conducting a jar test is the inclusion of a relatively new category of ingredients into tank mixes — micronutrients.

“The specialty fertilizer industry has really blossomed recently. It’s largely unregulated, however, and, by and large, it’s user beware,” says Wolf.

“Micronutrients are basically salts. They’re ionizable and you just don’t know how they are going to agree with other salts. Sometimes things don’t go so well — you can have flocculation, sedimentation and coagulation.”

Do a jar test for known combos

Wolf recommends doing a jar test even for product combinations you’ve used successfully in the past. Some products may have undergone a formulation change, for example, moving from a dry to a liquid formulation. Others might have undergone changes in manufacturing processes or have slightly different chemical signatures, depending on whether the products are generic or name brand.

Jar testing is only useful if it closely mimics the realities of your sprayer tank. If you pull murky water from a dugout to fill your sprayer tank, doing a jar test using clean water from your kitchen tap might not give you accurate results. The same holds true if you fill your sprayer with water from your deep well at 5 C but jar test using lukewarm water.

Time matters too — if you routinely spray half a tank, then leave the remainder overnight before completing the job, don’t expect accurate jar test answers inside of five minutes. Instead, leave the jar in your chemical shed and see what happens to products over time. How easy do they resuspend? Do they leave an oily residue that might indicate a more thorough sprayer cleanout will be required?

While jar testing is a great first step, keep in mind that a mason jar can’t recreate the realities of a sprayer tank. For example, if you mix an oil-based additive with a chemical that unexpectedly acts as an emulsifier, then turn on your sprayer’s pump, you can quickly end up with a sludge your jar test couldn’t have predicted. Also, some chemical interactions are subtle or invisible — a jar test won’t show if a particular mix reduces one chemical’s efficacy, for example. Still, while a jar test isn’t foolproof, it’s a good practice.

“It’s a kind of insurance. It might not catch all the problems, but it’ll catch some of them,” says Deveau.

Consider the math

Jar testing isn’t a completely simple affair. Calculating how a large tank translates to a tiny jar requires some mathematics and accurate measurements. However, testing kits are now available, complete with disposable pipets, tiny scoops and clear instructions.

One summer, Deveau and OMAFRA colleague Mike Cowbrough conducted more than 50 hands-on jar test demonstrations showing many ways tank mixing can go awry. Altogether, Deveau estimates approximately 2,000 farmers watched the demonstrations. Of the 2,000, Deveau says approximately 75 per cent reported they were familiar with the jar testing concept, but only about 10 per cent had actually conducted a jar test themselves.

Should more farmers consider jar testing?

“Without a doubt,” says Wolf. “Prevention is so much better than any other option.”

Consider the math, he says. If a tank mix goes bad and gels up, the first cost is the now wasted chemical. The second cost (and significant headache) is the disposal of an entire tank of useless, but still chemically active, product. The third and most problematic cost is the time it’ll take to clean that tank — a cost that should be measured in opportunity lost rather than man-hours wasted.

“If it costs you a day to clean out that tank, how much is that day worth? If it means you can’t spray 500 acres that absolutely needed to be sprayed that day, it’s worth a lot. It’s more than the hours. If you lost five bushels per acre because you didn’t treat that field on time, that could be $6,000 to $7,000. That’s an expensive mistake,” says Wolf. “The most powerful agronomic tool is doing things with the right timing. A really good job done at the wrong time isn’t worth much in our business.”

For an excellent resource and guide to jar tests, visit

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