Tank Mixing – 8 Steps Towards Getting It Right

Pre-plant herbicide application. Photo: Debra L Ferguson

Pre-plant herbicide application. Photo: Debra L Ferguson

When herbicide-resistant crops entered the market, two radical changes in farming practices occurred: First, weed control got easier, faster and less costly. Second, the art and science of tank-mixing herbicides gave way to a one postemergence herbicide-fits-all approach.



But it would not last long. Glyphosate-resistant weeds soon appeared on the farmscape and resistance to other herbicides followed. To manage resistance, weed scientists and other people dealing with the problem began recommending programs with multiple modes of action – including residual herbicides – with every application.

Tank mixes began making a big comeback, but there are challenges.

For Starters: Still Not Enough Tank Mixing Anyway

For one thing, producers rarely do enough tank mixing with new products and technologies coming on the market, says Bill Johnson, a Purdue University weed scientist. Dozens of premixes have also reduced the commitment to tank-mixing.

“We’ve also been too reliant on a single active ingredient and in the process, we retired a generation of farmers who really understood complex mixtures and how to make them work,” Johnson observes. “The flip side is that we have better spray equipment today that does a better job of agitating once products are in the tank. But we still have to get products in there in the right order.”

Patience, caution and knowledge are paramount for a successful tank mix, according to Johnson.

“Number one, there is an increased need for more complex mixtures to kill the weeds,” Johnson emphasizes. “Number two, so many herbicides are now off-patent, and we have a number of different companies supplying them. These materials may come from different formulations, so you never really know what you’re getting yourself into. Metribuzin from one company may not be the same as metribuzin from another company. There could be materials in the formulations that create mixing challenges.”

A mixing mishap can be costly, ineffective, time-consuming, or all of the above, Johnson points out. A common problem is physical incompatibility, caused by improper mixing, inadequate agitation or lack of stable emulsifiers in ECs (emulsifiable concentrates).

Curdling And Clogging: Not A Pretty Sight

Cottage cheese is great in lasagna, but when materials in your spray tank take on that texture, well, there’s no fast way to remove it.



“You can also be in a situation where you have hard water or you’re spraying under cool weather conditions (and thus cold spray water) and you have a lot of fine particles in your spray solution that plug up your screens,” Johnson explains.

The effect on spray coverage and control may be much less obvious than those clumps of goop floating in the tank, Johnson says.

“You may not be spraying at the optimum output or you might have a couple of nozzles that are putting out less than other nozzles. But that may proceed over a number of hours or a number of fields and result in a faulty application.”

This kind of issue also eats into efficiency during busy times of the season. As he points out, cleaning out a spray tank and all the inline and nozzle screens can take hours, even an entire day.

Spring Rush And The Challenge Of Slowing Down

Problems can also arise from rushing through the process, Johnson points out.

“Producers are so busy in the spring,” he says. “The weather windows to spray are narrow, and we get into a rush. That ultimately is what creates a lot of our problems.”

Producers should also be cautious with hard water cations and foliar fertilizers, particularly with glyphosate and 2,4-D applications, according to Johnson. “The active ingredients of both herbicides are weak acids in solution and may bind to cations present from hard water used as herbicide carrier or from foliar fertilizers added to spray solutions,” Johnson adds.

Beyond that, you might have a compatibility issue that’s not obvious to you in the spray tank, Johnson continues. “And you might reduce efficacy because you’ve put all these hard-water cations with a weak acid herbicide.”

Read more on cations and ammonium sulfate here.

Weather, temperature and commodity prices are big variables affecting a producer’s bottom line. But a proper tank mix is one factor that producers have the most control over, Johnson adds. “If you’re trying to distribute a uniform amount of product to the target, it’s of utmost importance that all of the application technology is optimized.

“Basically, we’re operating under such a narrow margin of controlling many pests – whether they’re weeds, insects or diseases – that must avoid shortcuts with the process.”

Things To Remember

Here are 8 steps to help people in the field avoid curdling, clogging, layering and other calamities that can result from improper techniques or mixing order mistakes.

#1. Read the label.

Labels specify mixing order, instructions for agitation, listings of products that should not be tank-mixed, recommended carrier volume, warnings about spray water carrier pH or mineral content and such.

#2. Shake it up.

 Make sure you shake product containers before you dispense them into the tank, so you thoroughly mix the active ingredient and inert ingredients together.

#3. Add water.

Fill the spray tank with 50% of required water volume.

#4. Mix it up.

Start the agitation and continue through the mixing process. Never add multiple products to the inductor simultaneously. Before adding the next product, flush the inductor with clean water. Remember that agitating too aggressively can cause foaming.

#5. Mix in order.

Add products based on formulation type. According to Avoid Tank Mixing Errors – Purdue Extension, the proper mixing order is:

  1. Water soluble packets.
  2. Dry formulations.
  3. Ammonium sulfate. Dry or solid anti-drift agents.
  4. Compatibility agents and anti-foamers.
  5. Dispersed liquid formulations.
  6. Liquid drift retardants.
  7. Remaining liquid formulations.
  8. Adjuvants.
  9. Micronutrients and liquid fertilizers.

#6. Be patient.

Wait three to five minutes before adding products after dry formulations. Dry formulations include wettable granules, soluble granules and dry flowables. If you use water-soluble packets, visually ensure that the bags have fully dissolved and the product has dispersed before you add more products to the solution.



#7. Add the remaining water.

In the process, continue agitation until the tank mixture appears uniform.

#8. Measure the pH.

Add pH adjusters at the end of the mixing process to ensure that the final spray solution is in the pH range specified by the product label. Use pH adjustors with care. Acidifiers can lower the pH of the tank mixture too much, causing some active ingredients to precipitate out of solution or to volatilize.

You can adjust pH before adding other products, but these materials can change the pH (especially glyphosate products and AMS), so you would still need to check pH after everything has been added to the tank.

A Link Between pH And Dicamba Movement?

In field and laboratory studies in Tennessee, tank pH is proving to be a very important factor for off-site emissions of dicamba, according to Tom Mueller, professor of weed science at the University of Tennessee.



Mueller has been studying dicamba drift and tank pH for several years. The studies are funded by the Tennessee Soybean Promotion Board.

Mueller’s study detects dicamba molecules, which he says may or may not be the result of volatility. But a pattern has emerged.

“Our studies have been very consistent,” Mueller said. “As you lower the tank pH, we get more emissions, which probably includes volatility. We also know that the higher the pH, the fewer the emissions.”

Adding PowerMax to dicamba formations has been shown to lower pH, Mueller adds.

More on pH and dicamba.