A common practice in crop protection is tank mixing pesticides and other agrichemicals such as adjuvants, fertilizers, biostimulants, and plant growth regulators. Promoted as an efficient way to apply inputs to crops, tank mixing is a routine procedure for most farmers.
Reasons for tank mixing pesticides with other agrochemicals
- Reduce crop damage and soil compaction associated with making multiple applications and passes across a field.
- Make timely applications based on weather conditions, crop stage, or pest life cycle stage.
- Improve the control of certain pests, e.g. tank mixing pesticides with different modes of action to control a resistant pest.
- Broaden the spectrum of targeted pests, e.g., tank mixing herbicides with insecticides enables targeting and controlling weed and insect pests.
- Enhance the efficacy of active ingredients by adding spray adjuvants.
Despite the many benefits of tank mixing, it must be done properly to achieve the desired outcome. If not done properly, tank mixing can be costly, time-consuming, and problematic. When tank mixing problems occur, they are collectively called incompatibilities.
What leads to incompatibilities?
- Each formulated product has a set of complex chemical structures.
- When a new agrichemical is added to the tank mix, it increases the likelihood of incompatibilities.
- When one product influences how other products in the mixture disperse, mix, and deliver.
- The most types of incompatibilities are common: physical and chemical.
Physical incompatibility
Products with ingredients that do not mix properly, which can block spray systems and disrupt chemical application. Some examples include when:
- Products will not be suspended in spray solution.
- Product clumps together.
- Product doesn’t completely dissolve.
- Oil residue appears in the tank.
- Product separates into layers.
- Spray solution foams excessively.
In some severe cases, physical incompatibility may cause the spray solution to form gels or cause solids to form. When this happens, operators have to drain and flush tanks, and clean all filters, screens, and nozzles. The residue and rinsate from the cleanup can be expensive to remediate and difficult to dispose of.
Chemical Incompatibility
The spray solution may mix effectively and look fine in the tank, but products may contain ingredients that are chemically incompatible. Some examples include:
- When spray solution creates physical incompatibilities, e.g., separation, formation of gels and clumps, etc.
- Spray solution that injures crops.
- Product which has reduced biological activity.
Chemical incompatibility may not always be obvious.
- Reduced efficacy is often the only observable effect.
- Visible crop injury may occur a few hours to several days following application.
- Most chemical incompatibilities arise from surfactants in the tank mix that are not compatible in mixtures.
Factors that may lead to incompatibility
- Combining formulations that have not been tested.
- Applying new tank mixtures using multiple products.
- Not following label instructions.
- Mixing products in the wrong sequence.
- Adding products when there is insufficient water in the spray tank.
- Adding products to the tank mix before previous products have time to dissolve and disperse.
- Mixing with too much agitation, which can cause foaming with liquid flowables; or too little agitation, which can cause dry formulations not to dissolve.
- Not considering compatibility when substituting water with liquid fertilizer.
- Not considering slower mixing times due to using cold water.
Eight Factors that will help you avoid tank-mix incompatibilities
- Check containers – to ensure that formulations that can separate into layers, e.g., suspension concentrates (SC), are thoroughly mixed before you use them.
- Follow label instructions – product manufacturers develop their mixing instructions based on laboratory tests and mixing and handling feedback from customers, researchers, and application specialists. Mixing guidelines from this information appears on the product label.
- Mix in the proper order – reduces occurrence of physical incompatibilities.
- Use the right water volume – typically, the tank must be half full of water before you add the first product.
- Be patient when adding products – some products require agitation while others take time to dissolve in water, especially when using cold water.
- Agitate properly – some products, such as water dispersible granules (WDG), wettable powders (WP), suspension concentrates (SC), and emulsifiable concentrates (EC) will settle out over time and require agitation. However, too much agitation may result in problems like foaming.
- Adjust for the carrier – the most common carriers used for applying pesticides are water and liquid fertilizer (e.g., 28% nitrogen). Understanding the differences between liquid fertilizer and water helps you determine how many products you can add to a mixture.
- Account for product and water temperatures – water temperature can influence the rate that products dissolve, disperse, emulsify, and flow.
The ABCs of Mixing Order
When using water as the carrier:
- Read all product labels.
- Shake all liquid product containers.
- Fill the spray tank with 50% of the required water volume.
- Start the agitation and continue through the mixing process.
- Add products based on formulation type in the following order:
- Water soluble packets.
- Dry formulations.
- Dry or solid anti-drift agents.
- Compatibility agents and anti-foamers.
- Dispersed liquid formulations.
- Liquid drift retardants.
- Remaining liquid formulations.
- Adjuvants.
- Micronutrients and liquid fertilizers.
- Wait three to five minutes before adding products after dry formulations.
- Add remaining water.
- Measure pH of your spray solution.
- Should always be done at the end of the mixing process to see if it is in the desired range.
- Use a pH adjuster, if necessary.
- Caution: Some products prohibit the use of pH adjusters, and this information can be found on the product label.
When using liquid fertilizer as the carrier:
- Read all product labels.
- Shake all liquid product containers.
- Fill the spray tank with 50 – 75% of the required liquid fertilizer volume.
- Never premix products.
- Add products based on formulation type as follows:
- Pre-slurries of water soluble packets and dry formulations.
- Pre-slurries of dry anti-drift agents.
- Compatibility agents and anti-foamers.
- Dispersed liquid formulations.
- Liquid drift retardants.
- Remaining liquid formulations.
- Adjuvants.
- Micronutrients.
- Add remaining liquid fertilizer to the tank.
- Inspect solution for signs of incompatibilities, e.g. separation.
- Continue to agitate the mixture until it is applied.
An important tool for compatibility testing …. The Jar Test
Pesticide application is an expensive venture and potential incompatibilities need to be identified prior to mixing the chemicals in the tank. One way you can determine if two chemicals are compatible is to conduct a ‘Jar Test’.
Jar Test
- A procedure that ensures that products will mix together well prior to mixing in the tank.
- Allows you to test product combinations for compatibility.
- Particularly important when mixing products in a liquid fertilizer carrier and when mixing more than two products in water.
- It simulates what occurs in a tank mixture.
- Provides evidence of physical incompatibilities such as separation, settling, inversions, and oil residue buildups.
- Always follow product label directions on how to conduct jar tests for specific products. For example, different products may require different water volumes for jar tests.
References
- Manuchehri, M.R. 2018. PSS-2789: Herbicide Mixing Order. https://extension.okstate.edu/fact-sheets/herbicide-mixing-order.html. Accessed, August 30, 2021.
- Whitford, F., Olds, M., et al. 2018. PPP-122: Avoid Tank Mixing Errors. https://ppp.purdue.edu/ppp-122-avoid-tank-mixing-errors-mobile-files/. Accessed, August 30, 2021.
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