Tank Mixing Calculations, Active Ingredient Rates, and Compatibility Testing

Tank Mixing Calculations, Active Ingredient Rates, and Compatibility Testing

Quick Answer: Combining multiple pesticides and liquid fertilizers in a single tank load saves time and fuel. However, applicators must verify physical and chemical compatibility. Follow the standardized W-A-L-E-S mixing sequence and perform a jar test prior to field mixing. Product load calculations convert labeled active ingredient (a.i.) rates into exact formulation quantities per tank load.

Tank mixing errors cause costly equipment downtime, gelled spray mixtures, clogged plumbing, reduced pest control efficacy, or severe crop phytotoxicity. Florida licensing exams thoroughly evaluate compatibility testing and tank mix math.

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Tank Mix Incompatibility: Physical vs. Chemical

1. Physical Incompatibility: Products fail to mix physically, forming heavy sludge, butter-like clumps, curd, flakes, or layer separation. Usually caused by improper mixing order, hard water, lack of agitation, or mixing EC formulations directly with liquid fertilizers.
2. Chemical Incompatibility: A chemical reaction alters the active ingredients, resulting in reduced pest control efficacy (antagonism) or unexpected crop destruction (phytotoxicity) without any visible physical change in the spray tank liquid.

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The Standardized W-A-L-E-S Tank Mixing Sequence

Unless product labels explicitly direct otherwise, add tank mix components to a tank filled 1/2 to 3/4 full with clean water using the industry-standard W-A-L-E-S protocol:

 1. W ──► Wettable Powders (WP) & Dry Flowables (WDG/DF)
 2. A ──► Agitate Tank Thoroughly until dry products disperse
 3. L ──► Liquid Flowables (F/FL) & Water-Soluble Concentrates (S/SL)
 4. E ──► Emulsifiable Concentrates (EC)
 5. S ──► Surfactants, Crop Oils, & Drift Adjuvants (add last)

Exam Tip: Remember W-A-L-E-S. Dry formulations (W) must always be added and fully dispersed in water before emulsifiable concentrates (E) or surfactants (S) are introduced.

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Jar Testing Protocol for Physical Compatibility

Perform a jar test before mixing large volumes in the spray tank:

1. Wear chemical-resistant PPE. Fill a 1-quart clean glass jar 1/2 full with the field water source.
2. Add proportional amounts of each pesticide formulation matching the tank mix ratio (typically 1 teaspoon per pint equivalent per rate per acre).
3. Follow W-A-L-E-S order, shaking the jar gently after adding each component.
4. Cap jar, invert 10 times, and let stand for 15 to 30 minutes.
5. Evaluate Results:
   • Compatible: Smooth, uniform suspension or easily re-dispersed mixture.
   • Incompatible: Heat formation, precipitation, clumping, grease layers, or separation into distinct oil/water bands that will not re-disperse.

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Active Ingredient (a.i.) Rate Mathematics

Pesticide labels may state rates in terms of formulation product (e.g., "2 quarts of Weed-B-Gone per acre") or active ingredient (e.g., "0.5 lbs a.i. of glyphosate per acre").

1. Dry Formulations (WP, WDG, DF, G)

Dry product concentrations are expressed as a weight percentage (%). An 80 WP contains 80% active ingredient (0.80 lbs a.i. per 1 lb product).

$\text{Lbs Dry Product Needed} = \frac{\text{Lbs Active Ingredient Required}}{\text{Percent Active Ingredient in Product (\%)}} \times 100$

2. Liquid Formulations (EC, F, UL)

Liquid formulation active ingredients are expressed in pounds of a.i. per gallon. A 4 EC contains 4 pounds of active ingredient per gallon of product.

$\text{Gallons Liquid Product Needed} = \frac{\text{Lbs Active Ingredient Required}}{\text{Lbs Active Ingredient per Gallon Product}}$

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Fully Worked Tank Load Scenarios

Worked Example 1: Dry Formulation Active Ingredient Calculation

Question: A grower needs to apply 1.5 pounds of active ingredient per acre of a herbicide formulated as a 75% WDG. How many pounds of 75% WDG product are required to treat a 50-acre field?

• Step 1: Calculate total a.i. needed: $\text{Total a.i.} = 50\text{ acres} \times 1.5\text{ lbs a.i./acre} = 75\text{ lbs a.i.}$
• Step 2: Convert a.i. to dry formulation weight: $\text{Lbs Product} = \frac{75\text{ lbs a.i.}}{75\%} \times 100 = 100\text{ pounds of 75\% WDG}$

Worked Example 2: Liquid Tank Load Preparation

Question: An applicator has a 400-gallon spray tank calibrated to deliver 20 GPA. The label specifies applying 1.5 quarts of a 4 EC herbicide per acre. How many acres can be sprayed per full tank, and how many gallons of herbicide product must be added per tank load?

• Step 1: Calculate Acres per Tank: $\text{Acres per Tank} = \frac{\text{Tank Capacity (gallons)}}{\text{Application Rate (GPA)}} = \frac{400\text{ gal}}{20\text{ GPA}} = 20\text{ acres}$
• Step 2: Calculate Total Product Needed per Tank: $\text{Total Quarts Product} = 20\text{ acres} \times 1.5\text{ quarts/acre} = 30\text{ quarts}$
• Step 3: Convert Quarts to Gallons: $\text{Gallons Product} = \frac{30\text{ quarts}}{4\text{ quarts/gallon}} = 7.5\text{ gallons of product per tank}$