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Calculating Dilutions

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:

  • Diluting 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.

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.


Diluting 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 gal recommended 
100 gallons ( Pounds of product needed in tank)

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)

Diluting 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 gal recommended
100 gallons ( Amount formulation needed in the tank)


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 tank (0.6)

0.6 pints x 16 ounces per pint = 9.6 ounces of formulation needed in 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 equipment applies per 1,000 square feet = Amount formulation needed in tank

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 much formulation 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) = Amount needed Amount equipment applies per 1,000 square feet (1.5 quarts) in tank (133 Tbsp)

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. To apply this amount to a given planting of a greenhouse or nursery crop, first 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.

Rate Calculations

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Dilution Tables:

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

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

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

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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.

Rectangles
The area of a rectangle is found by multiplying the length (L) by the width (W).

Example: Area = Length x Width
L = 125 feet
W = 40 feet
Area = 125 ft. x 40 ft.
Area = 5,000 sq. ft.

Circles
The area of a circle is the radius (half the diameter) times the radius-time 3.14.

Example: Area = radius x radius x 3.14
r = 35 feet

Area = 35 ft. x 35 ft. x 3.14
Area = 3,846.5 sq. ft.

Cubes or Boxes
The volume of a cube or box is found by multiplying the length (L) by the width (W) by the height (H).

Example: Volume = Length x Width x Height 
L = 125 feet

W = 40 feet
H = 12 feet
Volume = 125 feet x 40 feet x 12 feet
Volume = 60,000 cubic feet (feet3)

Cylinders
The volume of a cylindrical structure is found by multiplying the height by the are of the circle at the base. The area of the circle is the radius (half the diameter) times the radius times 3.14.


Example:
 Volume = Height x radius x radius x 3.14
Height = 125 feet

Radius = 35 feet
Volume = 125 feet x 35 feet x 35 feet x 3.14
Volume = 480,812 cubic feet (feet3)

Tent-shaped Spaces
The volume of a tent-shaped structure is found by multiplying the length (L) by the width (W) by the height (H) and dividing by 2.

Example: Volume = LxWxH
L = 125 feet 2

W = 40 feet
H = 12 feet
Volume = 125 feet x 40 feet x 12 feet
2

Volume = 30,000 cubic feet (feet3)

Quonset-style Structures
The volume of quonset-style structures is found by figuring the area of the end and multiplying that by the length.

To figure the area of the half-circle-shaped end, treat it as a whole circle, using the height from the ground to the highest point as the radius (H1). After you have figured the area of the whole circle (H1 x H1 x 3.14), divide by 2 to get the area of the half circle.

Example: H1 x H1 x 3.14 x L = Volume of half-circle
H1 = 12 feet 2 

L = 125 feet

12 ft. x 12 ft. x 3.14 x 125 ft. = 28,260 cubic feet
2

Greenhouse Volume Calculations:

EVEN SPAN STRUCTURE
sketch here
Area A and B = .5 (5 x 10) = 25
Area C = 20 x 5 = 100
Total Area = A + B + C = 100 + 25 + 25 = 100
Volume = Length x Total Area = 100 x 150 = 15,000 cu. ft.

ROUNDUP STRUCTURE
sketch here
Area A + B = .5 (r2) = 127
Area C = 5 x 18 = 90 sq. ft.
Total Area = A + B + C = 127 + 90 = 217
Volume = Length x Total Area = 50 x 217 = 10,850 cu. ft.

 

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