5.3 Adjuvants, Surfactants & Tank Compatibility
Key Takeaways
- Adjuvants are divided into Activator Adjuvants (surfactants, stickers, penetrants) and Utility Adjuvants (buffers, drift agents, antifoam).
- Non-Ionic Surfactants (NIS) reduce surface tension without electrical charges, enabling uniform spray coverage across waxy plant foliage.
- Buffers and acidifiers prevent alkaline hydrolysis, which rapidly breaks down organophosphate and carbamate insecticides in high pH water.
- The Jar Test evaluates physical compatibility on a small scale by mixing proportional components in a 1-quart glass jar and observing for 10-15 minutes.
- The WALES protocol dictates tank-mixing order: Wettable powders (W), Agitate (A), Liquid flowables (L), Emulsifiable concentrates (E), and Surfactants/Solutions (S).
5.3 Adjuvants, Surfactants & Tank Compatibility
Rarely is a commercial pesticide spray mixture composed strictly of water and a single active formulation. To optimize pesticide coverage, improve target adherence, prevent off-target drift, and save application time by combining multiple products in one tank load, applicators frequently utilize chemical additives known as adjuvants.
However, combining multiple formulations and additives in a spray tank introduces physical and chemical risks. Understanding adjuvant classifications, performing compatibility tests, recognizing incompatibility symptoms, and following the standardized tank-mixing sequence are critical responsibilities for certified applicators.
Defining Adjuvants: Utility vs. Activator Adjuvants
An adjuvant is any chemical substance added to a pesticide spray mixture to modify pesticide performance or physical spray characteristics. Adjuvants themselves possess no direct pesticidal activity against target pests. Adjuvants are categorized into two major functional classes: Activator Adjuvants and Utility Adjuvants.
PESTICIDE ADJUVANTS
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+-------------------------+-------------------------+
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ACTIVATOR ADJUVANTS UTILITY ADJUVANTS
(Enhance Target Efficacy) (Modify Tank / Spray Behavior)
• Surfactants (NIS, Cationic, Anionic) • Compatibility Agents
• Spreaders & Stickers • Buffers & Acidifiers
• Crop Oil Concentrates (COC / MSO) • Drift Control Agents (Thickeners)
• Penetrants • Antifoam / Defoamers
1. Activator Adjuvants
Activator adjuvants directly enhance the biological performance of the active ingredient once the spray droplet lands on the target leaf or insect surface.
- Surfactants (Surface Active Agents): Pure water has high surface tension, causing spray drops to bead up and roll off waxy leaf surfaces. Surfactants break water surface tension, allowing droplets to flatten out, spread uniformly, and cover a much larger leaf area.
- Non-Ionic Surfactants (NIS): The most common surfactant class in agriculture and turf. NIS carries no electrical charge, making it non-reactive with most pesticides and safe against crop foliage burn.
- Anionic (Negative Charge) & Cationic (Positive Charge) Surfactants: Less frequently used; can cause severe crop injury or react chemically with certain active ingredients.
- Stickers: Adjuvants that increase the adhesion of spray droplets to plant leaves and insect cuticles, preventing rain wash-off and weathering degradation.
- Penetrants & Crop Oil Concentrates (COC / MSO): Petroleum or methylated seed oils (MSO) that soften or dissolve waxy leaf cuticles, accelerating systemic absorption of foliar herbicides.
2. Utility Adjuvants
Utility adjuvants modify the physical properties of the spray solution inside the tank or spray line to improve application safety and equipment operation.
- Buffers and Acidifiers: Prevent alkaline hydrolysis—the rapid chemical degradation of organophosphate, carbamate, and synthetic pyrethroid insecticides when mixed with high pH (alkaline) water. Buffers lower and stabilize water pH between 5.5 and 6.5.
- Drift Control Agents (Thickeners & Deposition Aids): Increase spray solution viscosity, reducing the proportion of fine mist droplets (under 150 microns) that drift off-target.
- Compatibility Agents: Help blend physically incompatible formulations (such as liquid fertilizer carriers mixed with EC herbicides) to prevent clumping and separation.
- Antifoam (Defoaming) Agents: Suppress foam creation caused by intense hydraulic tank agitation of liquid formulations.
Tank Incompatibility: Physical vs. Chemical
Combining two or more pesticides or fertilizers in a single spray tank saves labor, fuel, and equipment wear. However, mixing incompatible chemicals leads to application failure or severe equipment damage.
Physical Incompatibility
Physical incompatibility occurs when products fail to mix together physically.
- Symptoms: Formation of heavy sludge, curdling, oil-water separation, gel flakes, clumping, or heavy precipitation that settles out and completely clogs spray strainers, pump lines, and nozzles.
- Causes: Improper tank-mixing order, insufficient water carrier volume, cold water temperature, or mixing dry powders directly with ECs without prior water dispersion.
Chemical Incompatibility
Chemical incompatibility occurs when a chemical reaction takes place between tank components, permanently altering the chemical structure of one or more active ingredients.
- Symptoms: Complete loss of pest control efficacy, severe target crop foliage burning (phytotoxicity), unexpected heat evolution in the tank, excessive gas production/foaming, or color change.
- Critical Factor: Chemical incompatibility cannot be remedied by adding compatibility agents or increasing agitation.
The Jar Test Protocol for Physical Compatibility
Before mixing large quantities of pesticides in a spray tank, applicators should perform a Jar Test to verify physical compatibility on a small scale.
Jar Test Procedure (Step-by-Step)
- Safety Equipment: Wear full PPE (gloves, eye protection, apron) in a well-ventilated area.
- Proportional Samples: Use a clean 1-quart glass jar. Fill the jar half full (1 pint) with the exact water or liquid fertilizer carrier that will be used in the spray tank at the same temperature.
- Add Products in Order: Add prospective pesticides and adjuvants in exact proportional amounts (typically 1 teaspoon per pint of carrier equals approximately 1 pint or pound per 100 gallons of spray mix).
- Invert and Stand: Cap the jar tightly, invert it 10 times to mix thoroughly, and let the jar stand undisturbed for 10 to 15 minutes.
- Observe Results:
- Compatible: The mixture remains a uniform solution, suspension, or milky emulsion with no separation or clumps.
- Incompatible: The mixture forms distinct layers, oily scum, heavy curdling, sludge, or gritty flakes. If a compatibility agent dissolves the clumps upon addition, the mix can proceed with that agent added to the main tank first.
Standardized Tank-Mixing Order: The WALES Method
When mixing multiple pesticide formulations and adjuvants into a spray tank, applicators must follow the standardized WALES sequence (or W-A-L-E-S protocol) to prevent physical clumping and formulation breakdown.
THE WALES TANK-MIXING SEQUENCE
W ===> Wettable Powders & Dry Flowables (WP, WDG, DF) into 1/2 filled tank
A ===> Agitate thoroughly until dry products are wetted and suspended
L ===> Liquid Flowables & Suspension Concentrates (F, SC) added next
E ===> Emulsifiable Concentrates (EC, E) added next
S ===> Surfactants, Solutions & Liquid Adjuvants (S, NIS, COC) added last
Detailed Steps of the WALES Protocol:
- Fill Tank Half Full: Fill the spray tank to 50% capacity with clean water carrier and start the tank agitation system.
- W - Wettable Powders & Dry Formulations (WP, WDG, DF): Add dry powders and granules first. They require maximum water volume and agitation to fully hydrate and suspend.
- A - Agitate Thoroughly: Allow agitation to run for 2 to 3 minutes until all dry formulations are completely dispersed and suspended throughout the tank volume.
- L - Liquid Flowables (F, SC): Add liquid suspensions and flowables next into the agitated tank mixture.
- E - Emulsifiable Concentrates (EC, E): Add solvent-based EC products next. (Adding ECs before dry powders are dispersed coats the dry particles in oil, preventing them from hydrating and causing massive clumping).
- S - Solutions & Surfactants (S, NIS, COC, Buffers): Add water-soluble liquids, surfactants, drift control agents, and remaining utility adjuvants last.
- Top Off Tank: Fill the remaining 50% of the spray tank with water carrier while maintaining continuous agitation until spraying is completed.
Summary of Tank Compatibility Rules
| Principle | Core Operational Rule |
|---|---|
| Jar Test Requirement | Perform a quart-jar test whenever mixing unfamiliar product combinations or using liquid fertilizer carriers. |
| WALES Sequence | Always mix dry formulations (W) first, agitate (A), add flowables (L), add ECs (E), and add surfactants/solutions (S) last. |
| Alkaline Hydrolysis Prevention | Add buffers/acidifiers to spray water when pH exceeds 7.0 to prevent insecticide degradation. |
| Never Mix Concentrates | Never combine concentrated pesticides directly together in an empty tank without water carrier. |
What is the primary function of a Non-Ionic Surfactant (NIS) when added to a herbicide spray tank mixture?
An applicator testing hard well water discovers a pH of 8.5. Which type of utility adjuvant should be added to prevent alkaline hydrolysis of sensitive insecticides?
During a Jar Test for physical compatibility, how long should the applicator allow the capped jar to stand undisturbed before evaluating the mixture for clumping or separation?
Following the standardized WALES tank-mixing protocol, in what order should Emulsifiable Concentrates (EC) and Wettable Powders (WP) be added to a half-filled spray tank?