2.3 Pesticide Formulations & Tank Mixing Compatibility

2.3 Pesticide Formulations & Tank Mixing Compatibility

Core Concept: Pure active ingredients (technical material) cannot be applied directly in field conditions; they must be processed into usable commercial formulations by combining the active ingredient (AI) with liquid or dry inert carriers, solvents, emulsifiers, and conditioning agents.

Selecting the correct formulation and executing proper tank mixing procedures are critical steps to prevent equipment clogging, pump damage, crop phytotoxicity, and hazardous chemical incompatibility.

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Breakdown of Liquid Formulations

Liquid formulations are manufactured for mixing with water or liquid fertilizer, or applied directly as concentrated liquids:

1. Emulsifiable Concentrates (EC or E)

• Composition: Active ingredient dissolved in an organic petroleum solvent, combined with emulsifiers.
• Appearance in Tank: Mixes with water to form a milky-white emulsion. Requires minimal agitation once mixed.
• Advantages: High active ingredient concentration, easy to handle and store, non-abrasive to pumps and nozzles.
• Disadvantages: Organic solvents are easily absorbed through human skin (high dermal toxicity risk). Solvents can deteriorate rubber hoses, gaskets, and pump seals, and may cause severe plant foliage burning (phytotoxicity). Petroleum solvents are flammable.

2. Solutions (S or Liquid Concentrates)

• Composition: Active ingredient dissolves completely in water or liquid carrier to form a true solution.
• Appearance in Tank: Clear liquid that does not separate or settle out.
• Advantages: Does not clog nozzles or strainers, non-abrasive, requires no agitation once thoroughly mixed.
• Disadvantages: Few technical AI chemicals are water-soluble.

3. Flowables (F or L) / Suspension Concentrates (SC)

• Composition: Solid active ingredient finely ground into a powder and suspended in a liquid carrier slurry.
• Appearance in Tank: Forms a suspension when mixed with water. Requires continuous mechanical agitation to prevent settling.
• Disadvantages: Highly abrasive to pump impellers, pressure regulators, and nozzle orifices (especially brass and plastic nozzles).

4. Microencapsulated (ME or M)

• Composition: Liquid or dry active ingredient encased in microscopic plastic polymer capsules suspended in a liquid carrier.
• Operation: After application, the polymer shell slowly breaks down, releasing the AI over an extended period.
• Advantages: Extended residual pest control, reduced acute handler toxicity.
• Critical Wildlife Hazard: Micro-capsules are identical in size to pollen grains. Foraging honeybees collect ME micro-capsules, carry them back to the hive, and feed contaminated pollen to larvae, causing colony breakdown.

5. Ultra-Low Volume (ULV)

• Composition: Near-pure active ingredient applied in extremely small spray droplet volumes (less than 0.5 gallons per acre) using specialized high-speed rotary atomizers. High drift hazard.

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Breakdown of Dry Formulations

1. Wettable Powders (WP or W)

• Composition: Dry, finely ground powder containing active ingredient, dry clay/talc carrier, and wetting agents.
• Appearance in Tank: Does NOT dissolve in water; forms a suspension.
• Advantages: Low dermal absorption risk compared to ECs, generally non-phytotoxic to crops.
• Disadvantages: Severe inhalation dust hazard when opening bags and measuring powder. Requires continuous, vigorous agitation in spray tanks. Highly abrasive to nozzles and pumps; clogs fine mesh strainers.

2. Soluble Powders (SP)

• Composition: Dry powder that dissolves completely in water to form a true liquid solution.
• Advantages: Non-abrasive, requires no agitation once dissolved.
• Disadvantages: Inhalation dust hazard during measuring and tank loading.

3. Dry Flowables (DF) / Water-Dispersible Granules (WDG)

• Composition: Active ingredient formulated into small, dust-free granules that quickly disperse into a suspension when added to water.
• Advantages: Eliminates the inhalation dust hazard of WPs while maintaining ease of measuring and container pouring.
• Disadvantages: Requires continuous agitation; abrasive to spray equipment.

4. Granules (G) & Pellets (P)

• Composition: Dry, coarse particles (clay, corn cobs, or walnut shells) impregnated with active ingredient. Applied directly as dry granules to soil or foliage using specialized granular spreaders.
• Advantages: Ready to use, no water carrier or mixing required, zero spray drift risk, low handler risk.
• Disadvantages: Requires specialized application equipment; does not adhere to foliage.

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Formulations Characteristics & Operational Comparison Matrix

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Adjuvants & Surfactants

An adjuvant is any substance added to a pesticide spray mixture to modify chemical activity or improve application performance:

• Surfactants (Surface Active Agents): Reduce the surface tension of water droplets, allowing spray drops to flatten, spread out, and wet waxy leaf surfaces uniformly.
• Crop Oil Concentrates (COC) & Methylated Seed Oils (MSO): Petroleum or vegetable oil additives that soften waxy leaf cuticles, enhancing systemic herbicide penetration.
• Stickers & Extenders: Increase spray droplet adherence to foliage, preventing rain wash-off and weathering.
• Buffering Agents & Water Conditioners: Adjust spray tank water pH to prevent alkaline hydrolysis (chemical breakdown of organophosphate and carbamate insecticides in alkaline water above pH 7.0) and tie up hard water cations ($Ca^{2+}, Mg^{2+}, Fe^{3+}$).
• Drift Control Agents & Anti-Foaming Agents: Increase spray droplet size to reduce wind drift, or suppress foam accumulation in agitated tanks.

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Tank Mixing & Compatibility Protocols

Applicators frequently combine two or more pesticides (e.g., herbicide + fungicide + insecticide) alongside liquid fertilizer and adjuvants to save time and fuel.

Incompatibility Types

1. Physical Incompatibility: Chemicals fail to mix properly, forming curd, sludge, clumping, heavy oily layers, or gel that clogs pumps and hoses.
2. Chemical Incompatibility: A chemical reaction occurs between products that alters efficacy (antagonism) or causes severe crop foliage burning (phytotoxicity).

The Jar Test Procedure

Before mixing large chemical batches, applicators must verify physical compatibility by performing a Jar Test:

1. Wear mandatory PPE (gloves, eye protection).
2. Fill a clear 1-quart glass jar half-full with the exact water or liquid fertilizer carrier source to be used in the field.
3. Add proportional amounts of each chemical component in the exact sequence planned for field mixing.
4. Cap the jar tightly, shake vigorously for 10–15 seconds, and let stand undisturbed for 15 to 30 minutes.
5. Inspect the Mixture: If the mixture remains uniformly dispersed or easily re-suspends upon gentle swirling, it is compatible. If heat develops, or if clumping, precipitation, layer separation, or cottage-cheese sludges form, the products are physically INCOMPATIBLE and must NOT be tank-mixed.

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Standard Tank Mixing Sequence (W-A-L-E-S Protocol)

To ensure proper dispersion and prevent tank gelling, products must be added to the spray tank in the industry-standard W-A-L-E-S order. Always check the product labels first — when a label specifies its own mixing order, the label controls.

1. Fill the tank: Fill 1/2 to 3/4 full with water or liquid carrier and begin continuous agitation. Agitation stays on for the rest of the sequence.
2. W — Wettable powders and dry formulations: Wettable Powders (WP), Dry Flowables (DF), and Water-Dispersible Granules (WDG). Pre-slurry dry powders in a bucket of water before adding. Allow full dispersion before moving on.
3. A — Agitate: Hold vigorous agitation until the dry products are completely dispersed and hydrated.
4. L — Liquid flowables and suspensions: Flowables (F), Suspension Concentrates (SC), and Microencapsulated (ME) products.
5. E — Emulsifiable concentrates: Oil-based EC and EW products. Oils added earlier would coat undispersed dry particles and prevent them from wetting out.
6. S — Solutions, surfactants, and adjuvants: Water-soluble liquids (S, SL), non-ionic surfactants, crop oil concentrates, drift-control agents, defoamers, and micronutrients last. Top off with water.

Memory hook: the letters track the physical state of what you are adding — dry solids first, then suspended solids, then oils, then true solutions and additives.