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Pesticide Tank Mix Incompatibility

Bob Herzfeld, Product Manager
Bob Herzfeld, Product Manager

The cause and fix

The anticipated shortages of pesticide products may force the industry to look for alternative products to fill the void if the first choice is unavailable. This could lead applicators and growers to use products that they are less familiar with. This could lead to “Tank Mix Incompatibility.”

Tank mix incompatibility will cause a host of problems that you really do not want to deal with. The headache of cleaning out a spray tank during a busy spring season is not easy or fun. Incompatibility issues cause financial loss not only due to the cost of lost material but also because of reduced yield caused by reduced pesticide efficacy.

Tank mix incompatibility can be triggered by several factors. Preventing incompatibility can be achieved by:
      • Familiarity with product labels.
      • Jar testing in advance.
      • Spray solution water quality.
      • Chemical properties of tank-mix partners.
      • Mixing order.
      • Amount of spray solution water.
      • Agitation.

Familiarity with product labels

Product labels have information about what to consider when using an active ingredient. It is important to always read labels, in particular when different products will be mixed. Chemical formulations can change over time, so it is important to read the labels even if a product has been used in previous years.

The fix. Always read labels to understand the product needs in a tank mix.

Labels provide usage instructions
Labels provide usage instructions

Jar Testing

Pesticide labels have straightforward recommendations about jar testing when tank mixing two or more pesticides or adjuvants. However, when four or more tank-mix partners are added, the chances of incompatibility increase.

The fix. Do a jar test to learn if products are compatible. To jar test, you should use the current product that will be used in the tank mix, not a leftover from previous years. This is because the formulation of the chemicals may have changed. Also, use the same water you use for the spray solution carrier. Finally, add the tank mix partners at the same ratio you would add to the spray tank. For more specific information, pesticide labels have jar test recommendations for you to follow.

Performing a jar test before mixing in a tank can prevent a lot of trouble
Performing a jar test before mixing in a tank can prevent a lot of trouble
A jar test can show incompatibility for tank mix partners

Spray solution water quality

Usually, up to 90% of the spray solution is water. Numerous pesticides are sensitive to a high pH and the hardness of the water. High pH causes hydrolysis for some pesticides, making them less effective. High pH can also reduce the solubility of certain pesticides. Also, water with a high dissolved mineral content can react with sensitive pesticides, lowering efficacy (e.g., glyphosate, 2,4-D).

Low temperatures can reduce the solubilization of the products. For example, ammonium sulfate used for water conditioning may take up to half an hour to fully solubilize in cold, hard water.

The fix. Use a high-quality water conditioner and/or a pH buffer. Use either an acid or alkaline buffer, depending on the chemistries being tank mixed. There are numerous formulations of alkaline/acid pH adjusters, water conditioners with multiple modes of action, and multifunctionals that include water conditioners on the market.

Tank Mix Partners

To reduce costly trips over the field, applicators are increasingly mixing several pesticides with nutrients in the tank. Each additive has unique properties that may or may not agree with other tank-mix partners. For example, liquid nitrogen products, like 28% and 32% UAN, and micro-nutrient products are commonly mixed with several other pesticides.

There are two different types of incompatibility, physical and chemical. Physical incompatibility is like mixing oil and water, which will separate into distinct layers. When chemical incompatibility occurs, the efficacy of the tank mix partners is decreased because they react with each other.

Physical Incompatibility

Oil- and water-based pesticides do not stay mixed by themselves. Physical incompatibility is visible in various ways.

      • Precipitation: active ingredients coagulate and fall out as solids to the bottom of the container.
      • Separation: spray solutions separate into layers within the tank. This will cause uneven distribution of pesticides across the field.
      • Coagulation: spray mixture coagulates into lumps, clumps, or creates a highly viscous solution that causes plugged filters, pumps, pipes, and nozzles.

Physical incompatibility can cause financial loss due to clogged equipment, causing lost time, potential equipment cost, and loss of pesticide & nutrients. In addition, uneven spray applications reduce pest control efficacy, which can lead to reduced yields or multiple applications.

The fix. When jar testing indicates a physical incompatibility problem, a compatibility agent could help as a preventive measure. Repeat the jar test, starting by adding the compatibility agent first followed by the lowest label recommended rate of each active to the jar. Compatibility agents cannot solve all compatibility problems, but they can be a valuable tool for specific challenging tank mixes.

Chemical Incompatibility

Chemical incompatibility occurs when one or more of the tank-mix partners chemically react with each other. It is often not visible while tank mixing, unlike the physical incompatibility described above. 

Chemical incompatibility can negatively affect spray quality, product uptake, and plant surface retention of the application. The effect of a chemically incompatible tank mixture may not always be evident at first. Visible crop injury (phytotoxicity) may occur a few hours to several days following an application. Sometimes, reduced efficacy is the only observable effect of chemical incompatibility. This may require additional applications and can decrease yield, harm crop quality, or both.

The fix. Use pesticide compatibility charts offered by universities and extension services, and always perform jar tests for unfamiliar or complex tank mixes.

Mixing Order

In the past, the mixing order of pesticides was described by the “WALES” method.  WALES is an acronym for W – Water Soluble Active Ingredients, A – Agitation, L – Liquid Active ingredients, E- Emulsified Concentrates & S – Surfactants. 

With the development of new pesticide formulations with different mixing characteristics, the WALES mixing acronym has become outdated. Microencapsulated suspensions and glyphosate with new high-load inert packages have moved the industry to use a new acronym, WAMLEGS.

WAMLEGS stands for:

W – Wettable Powders

A – Agitation (anti-foaming agents and buffers)

M – Microencapsulated suspension products

L – Liquid and soluble products

E – Emulsified concentrates

G – High-load glyphosate products

S – Surfactants

After the sequence above is completed, add micronutrients and other fertilizers.

Mixing in the wrong order can cause problems. For example, changing the mixing order of dry formulations or water-soluble bags and adding them after emulsified concentrates cause “wrapping” of the dry or bag material. This means the emulsifier will surround the dry particles or water-soluble bag and not allow them to dissolve, leading to clean-up issues and waste of time and money. Instead, create a pre-slurry with dry formulations and water-soluble bags first.

The fix. Follow all label instructions for the order of addition and perform a jar test if unsure about the compatibility of specific mixes.

Amount of Spray Solution Water

Growers and applicators resist transporting spray solutions with large amounts of water. This means they have to haul a lot of water, tying up equipment capacity while not covering as many acres.

The amount of water that is used to prepare a tank mix is crucial. Mixing instructions usually recommend filling the tank halfway with water first. If you use less water, the tank mix partners will not solubilize because the solution becomes saturated. Likewise, you could have mixing issues if you begin adding actives when the tank is less than 20% full.

Liquid Fertilizer as Part of the Carrier

It is common practice to use liquid fertilizer as part of the carrier along with water. However, spray solutions that use liquid fertilizers as part of the carrier can create their own set of problems. Liquid nitrogen fertilizers are close to saturation already, and therefore it may hinder the solubilization of ingredients.  

The fix. Always follow label instructions about spray carrier water quantity.


When tank mixing dry, granular, wettable powders, emulsified concentrates, or suspension concentrates, formulations with insufficient agitation will cause them to settle out over time.

Using too much agitation could cause foaming issues. High foam could cause water-dispersible granules (WDG) and wettable powders to float on top of the foam. When this happens, the products will not hydrate correctly. The product will swell and eventually fall to the bottom of the tank, possibly causing system plugging. Over-agitation also affects emulsified concentrates, causing the surfactants to separate from the surface of solid active ingredients. This could destabilize the solution causing clumping or a substance that looks like cottage cheese. This leads to more downtime and wasted product.

Proper agitation will keep the product in suspension when liquid fertilizers are used as part of the carrier in a tank mix with granular products.

Not taking enough time to mix the spray solution properly can cause a range of problems, as described above. However, taking enough time is essential to create a good tank mix that delivers a good application and the desired results.

The fix. always follow label directions for agitation, especially when using dry, granular, wettable powders, emulsifiable concentrates, or suspension concentrates.

With more complex tank mixes, incompatibility is more likely to become an issue. Prevent issues by following these steps

To Summarize

With new pesticide formulations introduced, using the proper compatibility protocol can keep you out of trouble. With transportation delays and product shortages, applicators and growers may need to switch to alternative products. Jar testing before tank mixing is essential. Use an adequate amount of water and know your spray water quality, hardness, and pH. Use the right amount of agitation. Follow the correct mixing order.  If you experience a compatibility issue, try to fix it with a compatibility agent. Read and follow all pesticide and adjuvant label recommendations to give yourself the best chance at a successful application.

Find more information about tank mix compatibility on the Purdue University Extension website. Excerpts from this bulletin were used in this tech update.

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