Section 5.1: Formulations, Compatibility, and Mixing/Loading Safety

Formulations, Compatibility, and Mixing/Loading Safety

To apply pesticides safely and effectively, an applicator must understand how different chemical formulations behave, how to combine them in a spray tank, and how to execute the mixing and loading process without causing environmental contamination or personal injury. This section explores the characteristics of liquid and dry pesticide formulations, procedures for compatibility testing, tank mixing sequences, and critical safety rules under federal and Massachusetts regulations.

Pesticide Formulations: Liquid vs. Dry

Pesticides are rarely sold as pure active ingredients. Instead, manufacturers combine the active ingredient (the chemical that kills or controls the target pest) with inert ingredients (solvents, carriers, adjuvants) to create a formulation. Formulations are generally divided into liquids and dry solids.

Liquid Formulations

1. Emulsifiable Concentrates (EC or E): These contain a liquid active ingredient dissolved in one or more petroleum-based solvents, with an emulsifying agent added. When mixed with water, they form a milky-white emulsion. ECs require moderate agitation. Exam Tip: ECs are easily absorbed through the skin because of the organic solvents they contain, representing a high dermal hazard. They are also abrasive to rubber hoses and seals in application equipment.
2. Solutions (S or SL): These consist of an active ingredient dissolved completely in a liquid carrier (usually water). Once mixed, they form a true solution that will not settle out or separate, requiring no further agitation.
3. Flowables (F or L): Designed for active ingredients that are solids and do not dissolve in water or oil. The active ingredient is finely ground and suspended in a liquid carrier. When mixed with water, they form a suspension that requires constant agitation to keep the particles from settling. Flowables are highly abrasive to nozzle tips.
4. Microencapsulated (ME or M): These contain liquid or solid active ingredients encased in micro-fine plastic capsules suspended in a liquid carrier. After application, the active ingredient is released slowly over time. While this increases applicator safety and extends residual control, it represents a severe hazard to honey bees. Bees mistake the capsules for pollen grains and carry them back to the hive, destroying the colony.

Dry Formulations

1. Wettable Powders (WP or W): Dry, finely ground formulations that look like dust. They do not dissolve in water; they form a suspension. WPs require vigorous and continuous tank agitation. Because they are highly abrasive, they wear down brass nozzles rapidly. Handling dry WPs represents an inhalation hazard during mixing.
2. Dry Flowables (DF) or Water-Dispersible Granules (WDG): Similar to wettable powders, but formulated as small, dust-free granules. When added to water, the granules break apart and form a suspension. They offer the same benefits as WPs but with a significantly reduced inhalation hazard during measuring and pouring.
3. Soluble Powders (SP or WSP): Dry formulations that dissolve completely in water, forming a true solution. Once dissolved, they require no agitation.
4. Granules (G): Dry, ready-to-use formulations containing a low percentage of active ingredient (usually 1% to 15%) adhered to an inert carrier like clay or ground corn cobs. They are applied directly to target sites without mixing with water. They pose a low drift hazard but require moisture (rain or irrigation) to activate.

Tank Mixing and Compatibility: The Jar Test

Applicators frequently mix two or more pesticides (or a pesticide and a liquid fertilizer) in the same tank to save labor, fuel, and time, and to expand the spectrum of pests controlled. However, mixing incompatible chemicals can cause severe problems.

Types of Incompatibility

• Physical Incompatibility: The products fail to mix. This results in the formation of flakes, crystals, gels, sludges, or oil separation (often called a 'clobber' in the tank). Physical incompatibility makes the mixture impossible to spray and can ruin pumps and nozzles.
• Chemical Incompatibility: The products mix without visible change, but a chemical reaction occurs that deactivates one or both active ingredients (antagonism), or makes the mixture highly phytotoxic (causing plant injury).

Conducting a Jar Test

To verify physical compatibility before mixing products in a large spray tank, applicators must perform a Jar Test:

1. Put on the required PPE for the most toxic product to be tested.
2. Obtain a clean, clear glass quart jar.
3. Fill the jar half full with the carrier (water or liquid fertilizer) from the same source and at the same temperature as will be used in the spray tank.
4. Add the products one at a time in the proper mixing order, mixing thoroughly after each addition. Use proportional amounts (e.g., 1 teaspoon of product per pint of carrier for every 1 pound or 1 pint of product per 100 gallons of tank mix).
5. Fill the remainder of the jar with the carrier.
6. Let the mixture stand for 10 to 15 minutes.
7. Observe the jar. If the mixture remains uniform, it is physically compatible. If it clumps, separates, heats up, gels, or forms a sludge, the products are incompatible and must not be tank-mixed.

Tank Mixing Order: The WALES Sequence

To prevent physical incompatibility, dry and liquid formulations must be added to the spray tank in a specific sequence. A standard, tested industry sequence is the WALES method:

• W - Wettable Powders, Dry Flowables, Water-Dispersible Granules, and Water-Soluble Packets: These dry formulations must be added first and allowed to disperse fully in the carrier.
• A - Agitation: Start the tank agitation system and add water to about 90% of the target volume. Ensure the dry products are completely suspended before adding the next ingredient.
• L - Liquid Flowables and Suspensions: Add flowables, liquid suspensions, and microencapsulated products.
• E - Emulsifiable Concentrates (EC): Add ECs next, allowing them to emulsify in the tank.
• S - Surfactants, Soluble liquids, and Adjuvants: Add soluble liquids, surfactants, and adjuvants last.

Mixing and Loading Safety and Backflow Prevention

Mixing and loading is the most hazardous phase of pesticide application because the applicator is handling the product in its concentrated, undiluted form. Dermal and inhalation risks are at their peak.

Personal Safety Rules

• Wear Extra PPE: Always wear a chemical-resistant apron, elbow-length gloves, and protective eyewear/face shield in addition to the standard label-required PPE when mixing and loading concentrates.
• Location: Perform mixing and loading outdoors or in a well-ventilated area, away from wells, surface water, and people.
• Spill Containment: Use a concrete containment pad that is impervious and sloped to a sump to capture any accidental spills or washwater.

Preventing Back-Siphoning

Back-siphoning occurs when a drop in water pressure causes pesticide-laden water to be sucked backward from the spray tank into the water supply. This can contaminate public drinking water or groundwater wells. Under Massachusetts law (333 CMR 10.00), applicators must prevent backflow using one of two methods:

1. Physical Air Gap: Maintain a physical separation between the water supply hose and the top of the spray tank. The air gap must be at least twice the inside diameter of the fill pipe, and never less than 1 inch.
2. Backflow Prevention Device: If an air gap is not possible, a certified backflow prevention device (such as a reduced pressure zone backflow preventer or double check valve assembly) must be installed on the water supply line.