Paul E. Sumner
The procedure below is based on spraying 1/128 of an acre per nozzle or row spacing and collecting the spray that would be released during the time it takes to spray the area. Because there are 128 ounces of liquid in 1 gallon, this convenient relationship results in ounces of liquid caught being directly equal to the application rate in gallons per acre.
Calibrate with clean water whenever possible. When applying materials that are appreciably different from water in weight or flow characteristics, such as fertilizer solutions, etc., calibrate with the material to be applied. Exercise extreme care and use protective equipment when active ingredient is involved. Check uniformity of nozzle output across the boom. Collect from each for a known time period. Each nozzle should be within 10 percent of the average output. Replace with new nozzles if necessary.
Step 1. Determine type of application to be made and select appropriate procedure from Table 1. Example: Herbicide Broadcast Procedure B.
Table 1. Calibration for Application of Herbicide, Insecticides, Nematicides Fungicides, or Liquid Fertilizers.
| Type of Application | Procedure | Coverage Basis |
| Row (See Note) | A | Row (gal/acre of row) |
| Broadcast | B | Broadcast (gal/acre) |
| Band | C | Broadcast (gal/acre of band |
Note: Determine and use average row spacing for modified row patterns. Use width of area covered per row as row spacing in skip row patterns.
Step 2. Using procedure A, B, or C below as selected in Step 1, determine appropriate calibration distance from Table 2.
Table 2. Calibration Distances for Various Row and Outlet Spacings or Band Widths.
| Row Spacing, Outlet Spacing or Band Width (Whichever Applies) (inches)2 |
Calibration Distance Distance1 (feet) |
| 48 | 85.8 |
| 46 | 88.8 |
| 44 | 92.8 |
| 42 | 97.2 |
| 40 | 102.1 |
| 38 | 107.5 |
| 36 | 113.4 |
| 34 | 120.1 |
| 32 | 127.6 |
| 30 | 136.1 |
| 24 | 170.2 |
| 20 | 204.2 |
| 19 | 214.9 |
| 18 | 226.9 |
| 12 | 340.3 |
| 10 | 408.4 |
| 8 | 510.5 |
1 To determine distance for spacing or band width not
listed, divide the spacing or band width expressed in feet into 340.3. Example:
for a 13" band the calibration distance would be 340 divided by 13/12 = 314.1.
2 To increase calibration accuracy for a wide nozzle spacing, multiply
calibration distance by a factor (for example, 2); then, divide the fluid amount collected
by the same factor for GPA. For narrow nozzle spacings with long calibration distances,
divide calibration distance by a factor (for example, 4); then, multiply the fluid amount
collected by the same factor for GPA.
Step 3. Measure and mark calibration distance in a typical portion of the field to be sprayed.
Step 4. With all attachments in operation (harrows, planters, etc.) and traveling at the desired operating speed, determine the seconds it takes to travel calibration distance. Be sure machinery is traveling at full operating speed the full length of the calibration distance. Mark or make note of engine RPM. You must operate machine at same speed used for calibration.
Step 5. With sprayer sitting still and operating at same throttle setting or engine R.P.M. as used in Step 4, adjust pressure to the desired setting. Machine must be operated at same pressure used for calibration.
Step 6.
Step 7. Measure the amount of liquid collected in fluid ounces. The number of ounces collected is the gallons per acre rate on the coverage basis selected in Table 1. For example, if you collect 18 ounces using procedure B or C the sprayer will apply 18 gallons per acre on a broadcast coverage basis. Adjust applicator speed, pressure, nozzle size, etc. to get recommended rate. If speed is adjusted, start at Step 4 and recalibrate. If pressure or nozzles are changed, start at Step 5 and recalibrate.
Step 8. To determine amount of pesticide to put into a sprayer or applicator tank, divide the total number of gallons of mixture to be made (tank capacity for a full tank) by the gallons per acre rate from Step 7 and add recommended amount of pesticide for this number of acres.
Step 9. Check for proper calibration every four to eight hours of use. Simply repeat steps 6 and7. If there is a difference of more than five percent of original calibration, check the system.
Use the recommended broadcast rates of pesticide to make tank mixtures for band applications when calibrating with procedure C. The number of gallons/acre determined in Step 7 is the gallons that will be applied to each acre actually treated.
To determine the gallons of spray mixture required to make a band application on a field, determine the number of acres that will be in the actually treated band. When all treated bands are the same width and all untreated bands are the same width, which is usually the case, the acres in the actually treated band can be calculated by placing the width of the treated band over the sum of the widths of the treated band and the untreated band, and multiplying this fraction times the number of acres in the field. Example: How many acres will actually be treated in a 30 acre field if a 12" band of chemical is applied over the drill of rows spaced 36" apart? The treated band width is 12". The untreated band width is (36" - 12") 24".
Acres actually treated will be:
The amount of mixture required will be 10 times the number of gallons per acre from Step7. The amount of chemical will be 10 times the recommended broadcast rate for one acre.
Check rate recommendations carefully as to application type, broadcast, band or row, and type of material specified, formulated product and active ingredient.
To determine amount of liquid pesticide required for a rate given in pounds of active ingredient per acre, divide recommended rate by pounds active ingredient per gallon stated on label. Example: Pesticide label states 4 lbs. active ingredient per gallon and recommends 1/2 pound active ingredient per acre. Amount of pesticide required: 1/2 lb./A divided by 4 lb./gal. = 1/8 gal./A.
To determine amount of wettable powder required for a rate given in pounds active ingredient per acre, divide recommended rate by percent active ingredient stated on label. Example: Pesticide label states powder is 50% active ingredient. Two pounds of active ingredient is recommended per acre. Amount of pesticide powder required: 2 lbs. AI/A divided by 0.5 AI/lb. = 4 lbs./A.
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