Adjuvants, Tank-Mix Order, and Compatibility

Adjuvants, Tank-Mix Order, and Compatibility

An adjuvant is added to a spray mixture to improve or modify performance, handling, or application. It is not automatically an inert or harmless material. The pesticide label may require an adjuvant, prohibit one, specify a type and concentration, or limit use by crop or weather. Follow every tank partner’s label and the adjuvant label.

Adjuvant functions

Surfactants reduce surface tension and improve wetting or spreading. Nonionic surfactants are widely used, but ionic character and concentration matter. Crop oil concentrates and methylated seed oils can improve penetration of waxy plant surfaces and can also increase crop injury under some combinations of product, crop stage, rate, and weather. Do not apply a universal 85°F cutoff; use the pesticide and adjuvant labels.

Utility adjuvants modify spray handling. Buffers or acidifiers adjust pH; water conditioners bind antagonistic ions; antifoam agents control foam; compatibility agents help maintain a mixture; drift-reduction agents change the droplet spectrum. A drift-reduction product does not legalize a spray quality, wind speed, or buffer that violates the pesticide label.

Water pH, hardness, temperature, turbidity, and dissolved minerals can affect solubility, stability, and efficacy. Test the actual carrier source and use conditioning only as a label or supported recommendation directs. Some pesticides break down in alkaline water, while acidifying other mixtures can create crop or equipment problems.

General mixing order

First follow any order printed on the product labels. When labels do not provide a complete order, the Illinois General Standards sequence is:

1. fill the tank one-quarter to one-half full with carrier;
2. begin agitation;
3. add utility agents if needed;
4. add suspension products, beginning with pre-slurried dry products such as WP, DF, or WDG, then wet flowables, suspension concentrates, or microencapsulated products;
5. add emulsifiable products such as EC;
6. add solution products such as S, SL, or SP;
7. add spray modifiers such as surfactants or oils if needed; and
8. finish filling with carrier while maintaining appropriate agitation.

This sequence replaces improvised claims that a mnemonic is itself a legal rule. A label may require induction, separate premixing, a different order, minimum water volume, or a delay between additions.

Compatibility jar test

A jar test can reveal physical incompatibility before a full tank is mixed. Wear label PPE and work in a ventilated, contained area. Use the same carrier water and temperature planned for the field. Add products to a clear labeled jar in the same proportions and order planned for the tank. Agitate after each addition, let the jar stand for the recommended time, and observe.

Never use an invented conversion such as “one teaspoon per pint equals one quart per 100 gallons.” Calculate each proportional amount directly. One quart per 100 gallons is 0.25 percent by volume; in one pint of carrier, that is about 1.2 milliliters, not a full teaspoon.

Separation that does not redisperse, flakes, crystals, curds, sludge, gel, excessive heat, or persistent foam indicate a problem. A compatibility agent may help only when labels and technical guidance support it. A mixture that looks uniform can still be chemically antagonistic, phytotoxic, ineffective, or illegal. A jar test cannot verify biological compatibility.

Biological interactions

Tank partners can be physically compatible yet change biological performance. An additive response equals the expected combined effects; synergism produces a greater effect than expected; antagonism reduces performance. Synergism can also increase crop or non-target injury. These outcomes depend on active ingredients, formulations, rates, water, target, and timing. Use only labeled combinations and supported directions. A jar test shows visible physical behavior, not additive, synergistic, or antagonistic biological effects.

Mixing safely

Confirm that all sites, crops, rates, application timings, and maximums overlap legally. Calculate the batch before opening containers. Add one product at a time with agitation, keeping the fill hose protected from backflow. Never climb over an open tank or use a hand to stir. If agitation stops, pause additions and restore safe mixing before continuing.

If the tank gels, heats, or separates, stop the operation. Keep the mixture contained, prevent overflow, and contact product manufacturers or the appropriate authority. Do not add random detergent, fertilizer, acid, alkali, or bleach, and never dump the mixture on the ground or into a drain.

For exam questions, explicit label order wins; otherwise use carrier, agitation, utility agents, suspensions, emulsifiables, solutions, spray modifiers, and final carrier.

Adjuvant rate calculations

Percentage volume-per-volume means adjuvant volume divided by final spray volume. A 0.25 percent v/v rate in 100 gallons is 0.25 gallon, or 1 quart. For a 20-gallon load, multiply 20 by 0.0025 to obtain 0.05 gallon, then convert to 6.4 fluid ounces. Percentage weight-per-weight and “per acre” rates are different and cannot be substituted. Calculate against the label’s stated final volume and use a measuring device accurate at that scale. Excess adjuvant can increase runoff, foam, crop injury, or equipment problems without improving control.