In modern agriculture, using pesticides effectively and responsibly is crucial. Farmers and agricultural professionals continually face the challenge of safeguarding crops from pests while minimizing environmental impact. This necessity is why horticulturists often need to grasp mathematics, especially when it comes to pesticide calculations, where the delicate balance between efficacy and sustainability is meticulously calculated. This article explains how to interpret pesticide labels and provides a simple framework for the mathematical skills needed to calculate the correct product amount for an application, using a few common examples.
Example 1
How many pounds of active ingredient are there in a 30-pound bag of a 50WP pesticide?
Note: "WP" refers to wettable powder (a dry pesticide formulation)
Solution
To answer this question, you need to first understand that 50WP represents 50% wettable powder. Wettable powder is a formulation where the product is made in a fine dust that easily dissolved in a solvent (typically water).
50% of the product presents active ingredient. Since we know the bag weighs 30 pounds, we can use the formula:
Base × Rate = Portion
The base value (B) is the weight of the bag. Thus, B = 30 lb.
The rate (R) is the percentage converted as a decimal. Thus, R = \(\frac{50\%}{100\%} = 0.5\)
Substituting these values into the formula, we can calculate the portion (P):
\[30 \times 0.5 = P\]
\[P = 15\;\mathrm{lb.}\]
Therefore, the amount of active ingredient is 15 lb.
Example 2
Q2. A 10G herbicide is to be applied at a rate of 2 lb. of product/1000 sq. ft. to 12,000 sq. ft. of lawns.
How much of the herbicide is needed?
Note: "G" refers to granules (a dry pesticide formulation)
Convert the application rate to pounds of active ingredient per 1000 sq. ft.
Solution
The recommend amount is given in the question as \(\frac{2\;\mathrm{lb.}}{1000\;\mathrm{sq. ft.}}\). Since we want to use this product for 12,000 sq. ft., we need to set up a proportion with the given ratio and solve the unknown (which we will call \(x\)).
Therefore, 24 lb. of product is required to fully cover a 12,000 sq. ft. lawn.
Using the same formula as before, we can find the portion of 2 pounds worth of product that is strictly active ingredient. The rate is given by the label 10G, where 10 represents 10% active ingredient per product weight. Thus, we will let rate (R) = 0.10 and base (B) = 2 lb.
\[2\;\mathrm{lb.} \times 0.1 = \mathrm{Portion}\]
\[P = 0.2\;\mathrm{lb.}\]
0.2 represents the weight of active ingredient (A.I.) when 2 lb. of product is given. Thus, the rate is \(\frac{0.2\;\mathrm{lb.\;A.I.}}{1000\;\mathrm{sq. ft}}\)
Extra Questions
The label on a granular (G) pesticide calls for an application rate of 0.75 pounds of a.i. per 1,000 square feet.
How many pounds of active ingredient would you need to treat an area that measures 125 feet long (l) by 90 feet wide (w). (Note: The area of a rectangle is calculated using the formula: \(l \times w\))
How much of a 25G product would you need to provide the amount of active ingredient needed to treat the entire area? (Note: "G" refers to granules (a dry pesticide formulation))
How many pounds of a 75S product are needed to supply 15 pounds of active ingredient? (Note: "S" refers to soluble powders (a dry pesticide formulation))
Solutions
The solutions to these questions can be found here:
