Calculating Dilutions

Pesticides


Applying the correct amount of pesticide is a must for responsible, effective pest management. The pesticide label and other recommendations tell you how much to apply. It is your job to:

  • dilute the formulation correctly

  • accurately calculate the size of the application site

  • apply the proper amount of pesticide to the treatment area

Diluting Pesticides Correctly


Unless you have the correct amount of pesticide in your tank mix, you cannot apply the correct amount of pesticide to the target. Under recommended or label rate pesticide may not kill the target pest(s) and too much can injure plants by causing phytotoxic reactions.

As a matter of fact, formulations such as wettable and soluble powders, emulsifiable concentrates and flowables usually are sold as concentrates and must be diluted in the spray tank. Water is the most common diluent, but oil, liquid fertilizers and other liquids are sometimes used. Consult the labeling or other recommendations to find out what diluent to use, how much the formulation should be diluted and in what order the materials should be added.

Performing a simple calculation based on the capacity of your sprayer, how your equipment is calibrated, how much area you want to treat and the recommended application rate.


Dilutions of Dry Formulations


Pounds Per 100 Gallons


Directions for dry formulations, such as wettable or soluble powders, may be given in pounds of pesticide formulation per 100 gallons of diluent. You must know how many gallons your sprayer tank holds (or the number of gallons you will be adding to the tank if the job requires only a partial tank load). Then use the following formula:


Gallons in tank x lbs per 100 gals recommended 100 gallons ( Pounds of product needed in a tank)


For example: Your spray tank holds 500 gallons. The labeling calls for 2 pounds of formulation per 100 gallons of water. How many pounds of the formulation should you add to the tank to make a full tank load? Hint: 100 gallons is one-fifth the volume of your tank so you will need 5 times more than 2 pounds of the formulation.


Gallons in tank (500) x lbs per 100 gallons (2) 100 gallons ( Pounds of product needed in a tank (10)

Dilutions of Liquid Formulations


Pints/Quarts/Gallons per 100 Gallons


Application rates for liquid formulations (EC, F, S, etc.) are often listed as pints, quarts or gallons per 100 gallons of diluent (carrier) or per acre. To make these calculations, use the same formulas you use for calculating dilutions for dry formulations, but substitute the appropriate liquid measure for “pounds” in the formulas. Use the following formula:


Gallons in tank x amount per 100 gals recommended 100 gallons ( Amount formulation needed in the tank)


For example: The labeling rate is 2 pints of pesticide formulation per 100 gallons of water. Your spray tank holds 30 gallons. How many pints of the formulation is needed in the tank?

Hint: Since your tank holds about one-third of the 100 gallons, you will need about one-third of the 2-pints per 100-gallon rate.


Gallons in tank (30) x pints per 100 gallons (2) 100 gallons ( Pints formulation neede the in a tank (0.6)

​0.6 pints x 16 ounces per pint = 9.6 ounces of formulation needed in a tank


Pints/Quarts of Formulation per 1,000 Square Feet


If the application rate is listed as pints or quarts of formulation per 1,000 square feet, use the following formula:

Gallons in tank x rate per 1,000 square feet Amount of equipment applies per 1,000 square feet

= Amount of formulation needed in a tank


For example: Your sprayer tank holds 10 gallons and applies 1_ quarts of spray per 1,000 square feet. The labeling directions indicate a rate of 5 tablespoons per 1,000 square feet. How many formulations do you need to make a tankful of spray? 


Hint: Your sprayer holds 10 gallons, which is 40 quarts, and 64 tablespoons = 1 quart.


Gallons in tank (10 gal = 40 qts) x rate per 1,000 square feet (5 Tbsp)

equipment applies per 1,000 square feet (1.5 quarts) in a tank (133 Tbsp)

= Amount needed

133 Tbsp ( 64 Tbsp per quart = 2 quarts plus 5 Tbsp (2.08 quarts) needed in the tank


Using water-only spray for calibration 


Some pesticides are registered for use at a certain amount per unit area, e.g. fl.oz. per hectare. Firstly, to apply this amount to a given planting of a greenhouse or nursery crop, calculate the size of the area to be treated. Secondly, determine how much spray volume is required to obtain satisfactory coverage by using a water-only spray applied to all or part of the planting. The volume required will vary with the size of the plants, amount of plant canopy and plant structure. Once the required volume has been determined for coverage of the treatment area, the appropriate amount of pesticide can be added to the tank to make the actual application.
Dilutions Rate Calculations

Wettable Powders: Number of ounces of wettable powder to use in small sprayers when amount per 100 gallons is known.

Emulsifiable Concentrates: Number of fluid ounces of emulsifiable concentrate (EC) to use in small sprayer when amount per 100 gallons is known.

Mist Blower: Quantity of emulsifiable concentrate (EC) needed to make a 25X concentrate.

Calculating Size of Target Sites for Fogs and Fumigants


To determine how much pesticide you need for a job, you must measure or calculate the size of the site to be treated. The following examples will help you to calculate the area and the volume of some enclosed spaces.

Greenhouse Volume Calculations:


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