First, select the GPA from the pesticide label or from other written recommendations. These recommendations usually assume that the material is applied uniformly (broadcast) over the entire area.
Second, select an appropriate speed of travel in miles per hour (MPH) as determined by ground roughness, etc.
Third, determine the effective spray width (W) in inches per nozzle. For boom type sprayers, W is equal to the nozzle spacing on the boom in inches. For band sprayers, W equals the band width in inches. For row crop sprayers, W equals the row spacing in inches divided by the number of nozzles per row.
Fourth, determine the required gallons per minute (GPM) for each nozzle from the formula:
GPM = GPA x MPH x W/5940
GPA = gals/act (to be applied uniformly over an acre) MPH = miles per hour
W = effective spray width, inches
Example 1
Twenty gallons per acre is to be applied at 4 MPH broadcast by a boom sprayer. Nozzles are spaced 20 inches apart on the boom.
GPM = 20 GPA x 4 MPH x 20 in./5940 = 0.27 gallons per minute
Example 2
Material is to be band sprayed at the broadcast rate of 20 GPA. Band width is 10 inches.
GPM = 20 GPA x 4 MPH x 10 in./5940 = 0.13 gallons per minute
Fifth, select a nozzle tip that will give the required GPM when operating within the desired pressure range.Example 3
Select a broadcast nozzle which will deliver 0.27 GPM. Refer to Fig. 13a. Follow down the column titled Capacity 1 nozzle GPM. An 8003 nozzle delivers 0.26 GPM at 30 PSI. Pressure could be increased slightly to obtain the desired capacity.
Example 4
Select a band spray nozzle which will deliver 0.13 GPM. Refer to Fig. 13b. Follow down the column titled Nozzle Capacity in GPM. An 80015E or a 95015E nozzle delivers 0.13 GPM at 30 PSI. Either nozzle could be used.
Check the sprayer for leaks at hose connections, etc.
Sixth, make certain that the proper size nozzle tip is installed in each nozzle.
Seventh, adjust the spray height to that recommended by the nozzle manufacturer. You will note from Fig. 13a that a 17 to 19 inch height is recommended for the broadcast nozzles listed.
Partially fill the spray tank with water. When filling the tank from surface waters or a public water supply, you must use an effective anti-siphon device to prevent backflow. Operate at the selected pressure and observe the spray patterns at each nozzle. If the spray patterns are not uniform, clean or replace the nozzle. Use containers (quart jars will work) to catch the spray from each nozzle for a measured length of time. Either measure the amount in ounces or measure the depth of water in each jar. Record the amounts and compare nozzles. Replace any nozzle with an output 5 percent more or less than the average of all nozzles.
When using flat fan nozzles, adjust the nozzle tips so that the spray patterns are about perpendicular to the direction of travel but with no interference of the patterns.
Set the nozzles at the manufacturers recommended height. Check uniformity of distribution as suggested earlier.
Example 5
| Nozzle No. | Nozzle Output ounces | Difference from Average ounces |
|---|---|---|
| 1 | 28 | 0.2 |
| 2 | 27 | 0.8 |
| 3 | 28 | 0.2 |
| 4 | 25 | 2.8 |
| 5 | 29 | 1.2 |
| 6 | 31 | 3.2 |
| 7 | 30 | 2.2 |
| 8 | 28 | 0.2 |
| 9 | 29 | 1.2 |
| 10 | 27 | 0.8 |
| 11 | 26 | 1.8 |
| 12 | 27 | 0.8 |
| 13 | 27 | 0.8 |
| Total 362 ozs . 13 nozzle = 27.8 ozs/nozzle | ||
| 5% variation = 27.8 x 0.05 = 1.4 ounces | ||
| Nozzles 4, 6, 7, and 11 exceed the 5% variation allowed and should be replaced. | ||