Mixing the pesticide thoroughly and carefully is an important step in good sprayer operation. Incomplete mixing results in varied application rates – too high at times, too low otherwise. Some chemicals, when mixed improperly with others, form a thick, mayonnaise-like mixture that will not spray properly and is difficult to clean out of the sprayer. Always read the label for proper mixing sequence, and test the compatibility of chemicals in a small container before mixing.
Generally, when preparing the spray mixture, fill the tank half full of water and pour in the correct amount of chemical while the pump is running. Then finish filling the tank. When using wettable powders, again fill the tank half full, make a slurry in a separate container or through an inductor system, and then add the slurry to the tank to ensure good mixing. Rinse the slurry container three times, pouring the rinsate into the tank. Finally, finish filling the tank with water.
You can spend hours in the field calibrating your sprayer to achieve the desired accuracy, but your efforts are wasted if you don’t know how much chemical to put in the tank. In a survey conducted by agricultural engineers at the University of Nebraska, 38 percent of the applicators failed to add the correct amount of chemical to the tank.
The amount of chemical needed per tankful depends on the recommended rate and the size of area you can treat per tank of spray. Calculations are the same whether you are using a manual backpack sprayer or a powered boom sprayer. The only difference is in the units. For small manual sprayers, the rate is in gallons or quarts per 1,000 sq ft, and for boom sprayers the application rate is usually given in gallons per acre. So, make sure you use the right units in tank mix calculations. Let’s assume now that you have a boom sprayer.
A sprayer has a 100-gallon tank, and it has been calibrated to apply 40 gallons per acre. The pesticide label recommends 2 quarts of commercial product per acre for broadcast application. Determine the quantity of pesticide to add to the tank:
| 100 gal per tank | = 2.5 A/tank |
| 40 gal per A |
Sometimes, chemical manufacturers give recommended rates in terms of active ingredient (A.I.) to be used per acre rather than the amount of total product per acre. In these cases, calculate the amount of material to be applied as shown in examples 2 and 3 for dry chemicals and liquid chemicals, respectively.
The application rate of the chemical applied with the sprayer in Example 1 is 2 pounds A.I. applied per acre. The material to be used is a wettable powder containing 50 percent A.I. Determine the quantity of chemical to add to the tank:
Lbs. of formulated product per A = 2 lbs/A x 100/50 = 4 lbs/A
Lbs. of formulated product per tankful = 4 lbs/A x 2.5 A/tank = 10 lbs/tank
The chemical you are applying with the sprayer in Example 1 is liquid. The recommendation calls for 2 pounds A.I. per acre. You have purchased a formulation that contains 4 pounds A.I. per gallon. Determine the amount of product needed per acre:
| Gal. of formulated product needed per A = | 2 lbs A.I./A | = 0.5gal/A |
| 4 lbs A.I./gal |