11.3 Tank-Mixing Procedures, Compatibility Testing & Equipment Cleanout

11.3 Tank-Mixing Procedures, Compatibility Testing & Equipment Cleanout

Tank-mixing involves combining two or more pesticide formulations and adjuvants into a single spray mixture. While tank-mixing saves operational time, labor, and fuel by addressing multiple pest problems in a single pass, improper mixing order or chemical incompatibility can cause severe equipment damage, crop phytotoxicity, or complete loss of pest control.

Benefits & Risks of Tank Mixing

• Operational Benefits: Reduces tractor field passes, minimizes soil compaction, saves fuel, and enables simultaneous weed, insect, and disease control.
• Potential Risks: Incompatible chemical combinations can cause immediate precipitation, tank gelling, pump seizure, nozzle clogging, reduced pest control efficacy (antagonism), or severe foliage burning on crops (phytotoxicity).

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Step-by-Step Tank-Mixing Protocol & W-A-L-E-S Sequence

Always consult product labels for specific mixing instructions and prohibited combinations. If the label does not specify a loading order, applicators must follow the standardized industry mixing sequence known by the acronym WALES (also written W-A-L-E-S).

Prerequisite: Fill tank 1/4–1/2 with carrier water and start continuous agitation, then add products in WALES order:

   W                       A                       L                       E                       S
Wettable Powders       Agitate                Liquid Flowables        Emulsifiable Concentrates   Solutions & Surfactants
(WP, WDG, DF)          (keep mixing)            (F, FL, SC)                   (EC)                    (S, SL, Adjuvants)
       |                       |                       |                       |                       |
       +-----------------------+-----------------------+-----------------------+-----------------------+---> Top Off Tank

Detailed WALES Loading Steps

Always begin by filling the spray tank 1/4 to 1/2 full with clean water or the designated liquid fertilizer carrier and start continuous agitation. The WALES letters then describe the order in which pesticide products and additives enter that partially filled, agitated tank:

1. W — Wettable Powders & Other Dry Formulations: Add dry formulations that require mechanical agitation to suspend: Wettable Powders (WP), Water-Dispersible Granules (WDG/DF), and similar dry products. Pre-slurry dry powders in a bucket of clean water before adding them to the spray tank to ensure rapid, complete dispersion and prevent clumping. Allow agitation to run for several minutes until dry particles are fully wetted and suspended.

2. A — Agitate: Maintain continuous, vigorous agitation after each addition so dry particles remain suspended and subsequent products blend uniformly. Never shut off agitation while dry formulations are in the tank.

3. L — Liquid Flowables & Suspensions: Add liquid suspensions and flowables: Flowables (F, FL), Suspension Concentrates (SC), and Microencapsulated (ME) products. These liquid formulations contain finely ground solid active ingredients suspended in a liquid base and blend easily into the agitated mixture.

4. E — Emulsifiable Concentrates: Add Emulsifiable Concentrates (EC). EC formulations consist of oil-soluble active ingredients, petroleum solvents, and emulsifiers. When mixed with water under agitation, ECs form a milky emulsion. Adding ECs after dry powders and liquid flowables prevents petroleum solvents from coating dry particles and preventing their dispersion.

5. S — Solutions, Surfactants & Adjuvants: Add water-soluble products, surfactants, crop oil concentrates, and other adjuvants last, unless the label directs a different sequence. Adding surfactants too early can cause excessive foaming that interferes with accurate tank filling and product metering.

After all products are added, fill the tank to the final volume with carrier while agitation continues, and apply the mixture promptly.

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Compatibility Concepts & Jar Testing Protocol

Physical vs. Chemical Incompatibility

Jar Test Procedure (Physical Compatibility Verification)

Before mixing large volumes of pesticides in a spray tank, perform a jar test to verify physical compatibility:

1. Safety Equipment: Put on chemical-resistant gloves and eye protection.
2. Container & Carrier: Obtain a clean 1-quart clear glass jar. Add 1 pint of the intended spray carrier (water or liquid fertilizer) from the exact source to be used in the spray tank.
3. Proportional Measuring: Calculate proportional amounts of each pesticide based on intended field application rates. As a general rule, 1 teaspoon of liquid or dry pesticide per quart of carrier corresponds to approximately 1 pint or 1 pound per 100 gallons of spray tank mix.
4. Sequential Addition: Add each product one at a time in the exact W-A-L-E-S sequence:
   • Add dry products (WP, WDG, DF) first; shake jar gently and allow 2 minutes for complete dispersion.
   • Add liquid flowables (F, SC); shake jar.
   • Add emulsifiable concentrates (EC); shake jar.
   • Add soluble liquids (S, SL) and surfactants; shake jar.
5. Stand & Inspect: Cap the jar tightly, invert it 10 times, and let it stand undisturbed for 15 to 30 minutes.
6. Evaluation:
   • Compatible: Mixture remains uniformly dispersed, or minor separation re-emulsifies easily with gentle shaking.
   • Incompatible: Separation, layering, heavy clumping, gelling, heat generation, or sludge formation occurs. Do not tank-mix these products.

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Equipment Cleanout & Triple-Rinsing Protocol

Immediate, thorough sprayer cleanout after completing an application is mandatory. Chemical residues left in spray equipment can harden, ruin pumps and valves, corrode metals, and cause catastrophic crop destruction when the equipment is subsequently used on sensitive crops (e.g., trace residues of dicamba or sulfonylurea herbicides left in a boom can destroy non-tolerant broadleaf crops).

   Step 1: Drain & First Rinse           Step 2: Neutralizing Wash               Step 3: Final Clean Rinse
  [Drain Tank -> Add 10-20% Water]   [Refill Water + Ammonia / Cleaner]      [Refill Clean Water -> Flush Boom]
  [Flush Lines -> Drain Completely]  [Circulate 15 Min -> Soak Overnight]    [Remove & Clean Strainers/Tips]

Step-by-Step Triple-Rinsing Protocol

1. First Rinse (Immediate Drain & Flush):

   • Immediately after emptying the spray tank, park the sprayer on an approved containment pad or target field site.
   • Drain the tank completely. Add clean water to fill the tank 10% to 20% of its capacity.
   • Flush clean water through the entire system—circulating through agitators, bypass lines, hose reels, spray booms, and nozzles for at least 10 to 15 minutes. Drain the system completely.

2. Second Rinse (Chemical Neutralization & Line Soaking):

   • Refill the tank with clean water and add a recommended commercial tank cleaning agent or specific neutralizing chemical:
     • Sulfonylurea Herbicides: Add household ammonia at a rate of 1 quart per 100 gallons of water. Ammonia raises pH, dramatically increasing sulfonylurea solubility so residues can be flushed out.
     • Phenoxy Herbicides (2,4-D, Dicamba): Add commercial tank cleaner, household ammonia, or activated charcoal slurry.
   • Circulate the cleaning solution through the entire pump, agitator, and boom system for 15 minutes. Shut off the boom and allow the solution to soak in hoses and boom pipes for several hours or overnight.
   • Flush the solution through the nozzles and drain completely.
   • Manual Component Cleaning: Remove all nozzle tips, nozzle strainers, in-line filters, and suction strainers. Clean them individually in a bucket of soapy water using a soft nylon brush. Never clean nozzle tips with wire or metal pins.

3. Third Rinse (Final System Rinse):

   • Refill the tank with clean water. Circulate clean water through the pump, agitator, and boom system, flushing thoroughly through all nozzles. Drain completely.

Proper Rinsate Disposal Rules

Rinsate is the pesticide-containing wash water generated during equipment cleaning. Rinsate must be managed responsibly and legally:

• Primary Disposal Method: Apply rinsate directly onto a labeled target application site at or below labeled rate limits.
• Secondary Disposal Method: Collect rinsate in dedicated storage tanks and use it as makeup water for subsequent spray batches of the same pesticide product.
• Prohibited Disposal Practices: NEVER discharge rinsate into ditches, storm drains, sanitary sewers, surface streams, sinkholes, near wellheads, or areas where runoff can contaminate groundwater.