How Should Pesticides Be Diluted Correctly? A Detailed Explanation of Concentration Calculation Methods

“The way pesticides are diluted directly affects how well they work and how the crops grow, so how exactly should they be diluted correctly?” “Is what the experts say and what is written on the label really what I think it means?” Questions like these often trouble farming friends, and after reading this article you will understand the correct way to dilute pesticides.

1. Dilution methods

Percentage concentration refers to the number of parts of pesticide or fertilizer contained in 100 parts of pesticide-fertilizer liquid or pesticide-fertilizer powder, expressed with “%”.

For example: 2% urea means that in 100 kg of urea solution there are 2 kg of urea and 98 kg of water.

2. Multiple concentration

This refers to the multiple of water added to 1 part of pesticide, usually expressed by weight.

For example: to prepare 700 times 50% carbendazim, use 1 part of 50% carbendazim and add 700 parts of water, then stir.

3. Conversion methods

The conversion formula for converting percentage concentration into ppm concentration is:

Number of parts of water added to 1 part of pesticide = percentage of pesticide × 1000000 / the ppm number to be prepared.

For example: to prepare 1 kg of a 2000 ppm solution from ethephon with a content of 40%, the amount of water added to the ethephon is 40% × 1000000 / 2000 = 200 parts.

4. Conversion into multiple concentration

Divide the percentage by the ppm number and move the decimal point 4 places to the right to get the dilution multiple.

For example: for 40% ethephon at 1000 ppm, when converting to multiple concentration, use 40 ÷ 1000 = 0.04, move the decimal point 4 places to the right, and you get 400 times.

5. Method of adding water

When several pesticides are mixed and used, you do not add water once for each pesticide added; instead, all the pesticides are calculated at the same 1 part of water for concentration.

For example: to prepare 500 times urea plus 1000 times thiophanate-methyl, use 2 parts urea plus 1 part thiophanate-methyl plus 1000 parts water. In addition, when adding water, a mother solution should first be prepared, that is, first use a small amount of warm water to dissolve the pesticide liquid, then add water to the required concentration and dissolve fully, so as to improve efficacy and prevent pesticide damage.

How should pesticides be diluted correctly?

I. Methods for expressing pesticide concentration

1. Percentage concentration: refers to the number of parts occupied by the active ingredient in 100 parts of pesticide, usually expressed as (%).

2. Parts per million concentration: refers to the number of parts occupied by the active ingredient in 1,000,000 parts of pesticide, with the symbol PPm (or micrograms/mL; milligrams/L; grams/cubic meter, etc.).

3. Multiple method (that is, dilution multiple): refers to the multiple of water or other diluents (fine soil, granules, etc.) added when commercial pesticides are diluted. When diluting 100 times or less, the 1 part occupied by the original pesticide must be deducted in the calculation, for example: diluting 50 times means using 1 part of the original pesticide plus 49 parts of diluent. When diluting more than 100 times, the part occupied by the original pesticide is not deducted in the calculation, for example: diluting 600 times means using 1 part of the original pesticide plus 600 parts of diluent.

II. Conversion between concentration expression methods

1. Conversion between percentage concentration and parts per million concentration: parts per million concentration (ppm) = 10000 × percentage concentration.

2. Conversion between the multiple method and percentage concentration: percentage concentration (%) = (original pesticide concentration / dilution multiple) x 100.

III. Calculation methods when diluting pesticides

1. Calculation by active ingredient

(1) Find the amount of diluent (water or filler, etc.) to use:

① Dilution below 100 times: amount of diluent = weight of original pesticide x (original pesticide concentration - prepared pesticide concentration) / prepared pesticide concentration.

② Dilution above 100 times: amount of diluent = weight of original pesticide x original pesticide concentration / prepared pesticide concentration.

(2) Find the amount of pesticide to use:

Amount of original pesticide used = weight of prepared pesticide x prepared pesticide concentration / original pesticide concentration.

2. Calculation by the multiple method (without considering active ingredient content)

(1) Dilution below 100 times: amount of diluent = weight of original pesticide × dilution multiple — weight of original pesticide.

(2) Dilution above 100 times: amount of diluent = weight of original pesticide × dilution multiple.

(3) Find the amount of pesticide to use: amount of original pesticide used = weight of prepared pesticide / dilution multiple

(4) Find the dilution multiple:

① Find the dilution multiple from the concentration ratio: dilution multiple = original pesticide concentration / prepared pesticide concentration.

② Find the dilution multiple from the weight ratio: dilution multiple = weight of prepared pesticide / weight of original pesticide.

3. Conversion by concentration and concentration units:

Concentration of a solution: solution concentration can be divided into three categories: mass concentration (such as mass percentage concentration), volume concentration (such as molar concentration, equivalent concentration) and mass-volume concentration.

(1) Mass percentage concentration

The concentration of a solution expressed as the percentage of the mass of the solute in the total mass of the solution is called mass percentage concentration, expressed with the symbol %. For example, 25% glucose injection means that 100 injectable solution contains 25 grams of glucose.

Mass percentage concentration (%) = solute mass / solution mass 100%

(2) Volume concentration

① Molar concentration: the concentration of a solution expressed as the number of moles of solute contained in 1 liter of solution is called molar concentration, expressed with the symbol mol. For example, if 1 liter of concentrated sulfuric acid contains 18.4 moles of sulfuric acid, then the concentration is 18.4 mol. Molar concentration (mol) = number of moles of solute / solution volume (liters).

② Equivalent concentration (N): the concentration of a solution expressed as the number of gram equivalents of solute contained in 1 liter of solution is called equivalent concentration, expressed with the symbol N. For example, if 1 liter of concentrated hydrochloric acid contains 12.0 gram equivalents of hydrochloric acid (HCl), then the concentration is 12.0 N. Equivalent concentration = number of gram equivalents of solute / solution volume (liters).

(3) Mass-volume concentration

The concentration expressed by the mass of solute contained in a unit volume (1 cubic meter or 1 liter) of solution is called mass-volume concentration, expressed with the symbol g/m3 or mg/L. For example, if 1 liter of chromium-containing wastewater contains 2 milligrams of hexavalent chromium, then the concentration of hexavalent chromium is 2 milligrams/liter (mg/L).

Mass-volume concentration = mass of solute (grams or milligrams) / volume of solution (cubic meters or liters).

4. Conversion formulas for concentration units

1) Equivalent concentration = 1000.d mass percentage concentration / E

2) Mass percentage concentration = equivalent concentration E / 1000.d

3) Molar concentration = 1000.d mass percentage concentration / M

4) Mass percentage concentration = mass-volume concentration (mg/L) / 104.d

5) Mass-volume concentration (mg/L) = 104 mass percentage concentration

5. ppm is a percentage by weight

ppm = mg/kg = mg/L

That is, 1 ppm = 1 ppm = 1000 ug/L

1 ppb = 1 ug/L = 0.001 mg

Where: E — gram equivalent of the solute; d — specific gravity of the solution; M — molar mass of the solute.

IV. PPM concentration conversion method

PPM is a concentration unit commonly used internationally, because PPM is an English abbreviation, not the name of a calculation unit; that is to say, 1 PPM = 1x10^-6, meaning 1 PPM is a concentration of one part per million.

1G of a drug at 100% concentration diluted in 1000KG of water is a 1PPM concentration; if the effective ingredient content of the drug concentration is 50%, then 1G of a drug at 50% concentration diluted in 500KG of water is a 1PPM concentration.

For example: to find how many times 500PPM GA3 (content 100%) needs to be diluted with water?

100/500X10000=2000 times

That is, 1G diluted in 2000G of water is a 500PPM concentration; the conversion formula can be substituted: pesticide active ingredient content (%) / target effective concentration of the pesticide liquid (PPM) X 10000 = water dilution multiple.