Application rates and settings for insecticide metering units on planter hoppers are usually given on the chemical label. However, correct rates can be attained only if the application units are calibrated properly because each insecticide flows differently depending on its density, particle size, type of carrier used and relative humidity. Therefore, the setting used for one 15G may not be the same as that needed for another 15G. Follow steps below to calibrate your applicator.
1. Read the label and determine the rate of material you want to apply (for corn rootworms this is usually 1.2 oz. a.i./1000 row ft. or 8oz of a 15G, or 6 oz. of a 20G formulation/1000 row ft; 4 oz of a 3G at 0.12 oz. a.i./1000 row ft).
2. Fill the insecticide boxes and attach a plastic bag or a calibration tube to each applicator tube.
3. Open the metering units to a beginning setting of the previous year's setting or that suggested on the insecticide label.
4. Measure out 250 feet and operate the planter at planting speed over this distance. Collect the granules.
5. Weigh the amount collected, or use a calibration tube provided by the product manufacturer to determine the weight per 250 row ft.
6. Multiply the amount collected by 4 to determine amount per 1000 row ft. Compare this with the recommended amount per 1000 row ft.
7. Repeat steps 1 through 6 above until the difference between the desired (intended) rate and the measured rate in step 6 is less than 5% of the intended rate.