Pesticide Equipment Calibration

Calibration is the process of measuring and adjusting the amount of pesticide your equipment will apply over a target area. Periodic calibrations of sprayers, dusters, and granule distributors are necessary to ensure accurate delivery rates of pesticides per acre. Calibrations are made by measuring the total gallons of water applied per acre, in the case of sprayers, and the total pounds of dust or granules applied per acre, in the case of dust and granule distributors. Too little spray or dust applied results in inadequate distribution of toxicant over plant surfaces. Control is usually poor, and additional applications are required. Too much per acre is hazardous for the applicator, is frequently injurious to plants (phytotoxic), and could lead to excessive residues if applied close to harvest.

Sprayer Calibration

Boom Sprayers

Before Calibrating:

• Thoroughly clean all nozzles, screens, etc., to ensure proper operation.
• Check to be sure that all nozzles are the same, are made by one manufacturer, and have the same part number.
• Check sprayer discharge and calculate gallons per minute. Run the sprayer at a certain pressure and catch the discharge from each nozzle for a known length of time. Check the spray patterns of all nozzles for uniformity and replace nozzles that do not have uniform patterns or do not fill containers at the same rate. If there is more than 10% variation between any nozzles, all the tips should be replaced. Collect all the discharge, measure the total volume and convert the volume to gallons. Divide this volume by the time in minutes to determine discharge in gallons per minute. When it is not convenient to catch the discharge from each nozzle, a trough may be used to catch the total discharge.
• Select an operating speed. Note the tachometer reading or mark the throttle setting. When spraying, be sure to use the same speed as used for calibrating. Careful control of ground speed is very important for accurate spray application. Select a gear and throttle setting to maintain constant speed. A speed of 2-3 miles per hour is desirable. From a "running start," mark off the beginning and ending of a 30-second run. The distance traveled in this 30-second period divided by 44 will equal the speed in miles per hour. Example: At a tractor speed of 1 mile per hour, you would travel 88 feet in 1 minute, 44 feet in 30 seconds or 500 feet in 5 minutes and 41 seconds.
• Select an operating pressure. Adjust pressure to desired psi according to the nozzle manufacturer. Do this while pump is operating at normal speed and water is actually flowing through the nozzles. This pressure should be the same during calibration and field spraying.

Calibration Using the Jar Method:

1. Measure a course on the same type of surface (sod, plowed, etc.) and same type of terrain (hilly, level, etc.) as that to be sprayed, according to nozzle spacing as shown in the table below. This distance is equivalent to 1/128th of an acre.

   Nozzle Spacing (in.)	16	20	24	28	32	36	40
   Course Length (ft.)	255	204	170	146	127	113	102

2. Time the seconds it takes the sprayer to cover the measured distance at the desired speed in the same field conditions that you are spraying. Average several runs. This is the time required to cover 1/128 acre.
3. With the sprayer standing still, operate at selected pressure and pump speed/engine RPM. Catch the water from each nozzle for the number of seconds measured in step 3. Any 1-quart or larger container, such as a mason jar or measuring cup, if calibrated in fluid ounces, can be used. You can also use a specially designed calibration jar; if you buy one, follow the manufacturer’s instructions. Make accurate speed and pressure readings and jar measurements. Make several checks. Keep in mind that you are collecting less than a quart of liquid to measure an application rate of several gallons per acre for many acres.
4. Determine the average output per nozzle in ounces. If the output from any particular nozzle is more than 5 percent higher or lower than the average, check for clogs, clean the nozzle (with compressed air!), or replace the nozzle. Replace all nozzles if the average output is more than 15% more than a new nozzle’s output (from the manufacturer’s chart or discharge test). Repeat steps 4 and 5 after cleaning or replacing any nozzles. The average  ounces of output per nozzle equals the application rate in gallons per acre. For example, 1 oz. output = 1 gallon per acre.

Calibration Using the Tank-Fill Method:

1. Fill sprayer with water.
2. Spray a measured area (width of area covered x distance traveled) at constant speed and pressure selected from manufacturer's information.
3. Measure amount of water necessary to refill tank (gallons used).
4. Multiply gallons used by 43,560 and divide by the number of square feet in area sprayed. This gives gallons per acre.
5. Add correct amount of spray material to tank to give the recommended rate per acre.

EXAMPLE:
Assume:

• 10 gal of water used to spray an area 660 ft long and 20 ft wide
• Tank size - 100 gal
• Spray material - 2 lb formulated product/A

Calculation:
      gal used x 43,560       =       10 x 43,560       =        33 gal/A
          area sprayed                        660x 20                      
 
       tank capacity             =        100 (tank size)   =        3.03 acres sprayed
           gal/A                                             33                                  per tank
 
       3.03 x 2 (lb/A) = 6.06 lb material per tank

Backpack Sprayers

Growers with diverse crops and small plantings often need to be able to apply pesticide to beds or plots of several hundred square feet. It is important to use the correct amount of pesticide in your backpack sprayer when spraying a small area, to mix and spray safely, and to follow the label instructions.

All measuring and mixing utensils used with pesticides or other chemicals should be clearly labeled with warnings that they are only to be used for measuring and mixing pesticides. Measuring equipment should be locked in the pesticide storage area. All equipment calibration should be done on the same surface to which the pesticide will be applied and at the same speed, pressure, etc.

Maintaining constant pressure can be difficult with sprayers that depend on continual hand pumping. To help with backpack sprayer calibration and application, constant flow nozzles are available. G.A.T.E. LLC manufactures a CF Valve that delivers a constant 14.9 psi recommended for spraying herbicides and a 21 psi for insecticides and fungicides. These are designed to deliver the same pressure and flow rate no matter what the pressure in the tank is above the designated pressure and shut off if the pressure in the tank falls below the designated pressure. SOLO makes a "pressure limiting valve" that actually has three settings of 5, 10 and 15 psi for their backpack sprayers that does the same thing.

Calibration will vary with the crop, crop stage, amount of canopy, and location of target pest in the crop. Seedlings will require far less material than a fully grown canopy. Match the amount of pesticide to the amount of water needed to spray the crop area at the target crop stage.

For products with rates listed in amount/acre:

1. Calculate what portion of an acre is being sprayed. Determine sq ft of area to be sprayed (multiply bed or canopy width by row length by number of rows). Calculate what proportion of an acre this is (it may be a small fraction of an acre):
   
   Proportion of acre to be sprayed ÷ 43,560 sq ft per acre = number of sq ft to spray
    
2. Calculate how much pesticide to use. Multiply the label rate per acre for the crop and pest times the proportion of an acre to be sprayed.
   
   Amount of pesticide needed =  amount per acre x proportion of acre to be sprayed

3. Measure water needed per sq ft of crop. Add a known amount of water (e.g., 1 or 2 gallons) to the tank. Spray the water as if you were actually spraying your field. Remember, you must maintain constant pressure, constant walking speed, and consistent nozzle height and boom setup or wand motion to achieve the coverage you need. This amount will change with different crops and size of crop canopy. When the water is gone, stop and mark the spot. Measure the area you sprayed and calculate sq ft (length of swath x width). Calculate how many gallons (or fluid ounces, for smaller areas) are needed per sq ft.
   
   Gallon per sq ft = number of gallons used ÷ number of sq ft sprayed
   
   This can also be calculated by timing how long it takes to spray a known area, then collecting the output for the same amount of time, at the same pressure. Divide the amount used by the area sprayed.
    
4. Determine total water needed:
   
   Gallons of water needed  =  gal per sq ft x number of sq ft to be sprayed
    
5. Mix the required amount of pesticide in required amount of water. Most commonly, it is best to add half the water, add the pesticide, agitate, then add the remaining water. Spray, using the walking speed, pressure, nozzle and boom setup or wand motion that you used for calibrating.

For Products That Give Rates for Backpack Sprayers. Some pesticide labels provide a rate of product to use per gallon, for backpack sprayers or smaller areas. If this is given, it is still important to calibrate to determine the amount of water used per unit area (sq ft). Add the labeled rate pesticide per gallon of water, adjusting the rate to match the fraction or number of gallons that will be used.

Calibration for Granular Applications

The application equipment for granular fertilizer, herbicides, insecticides, etc. in many cases was not designed as precision equipment; therefore, extra care must be taken in calibration to get the results desired. Application rates of granular application equipment are affected by several factors: gate openings or settings, ground speed of the applicator, shape and size of granular material, and roughness of the ground. It takes a conscientious operator, effort, knowledge of equipment, and calibration to achieve accurate application rates. The first step to good application is to be sure the equipment is prepared for operation. Be sure all controls are free and work properly. Check and lubricate moving parts as necessary, remove corrosion, and tighten loose nuts and bolts.

Broadcast Applicators (Gravity-Drop or Spinner Applicators)

1. From the label, determine the application rate.
2. From the operators manual, set dial or feed gate to apply desired rate.
3. On a level surface, fill hopper to a given level and mark this level.
4. Measure test area. Length of run will depend on size of equipment. It need not be one long run but can be multiple runs at shorter distances.
5. Apply material to measured area, operating at the speed applicator will travel during application.
6. Weigh amount of material required to refill hopper to the marked level.
7. Determine application rate:

                                                 number    x        length of      X       width of
      Area covered      =               of runs                 run (ft)             application (ft)
           (acres)                                                       43,560

     Application    =       amount applied (pounds to refill hopper)   
        rate (lb/A)                          area covered (acres)                             

• NOTE: Width of application is width of the spreader for drop or gravity spreaders. For spinner applicators, it is the working width (distance between runs). Check operator's manual for recommendations, generally one-half to three fourths of overall width spread.

EXAMPLE:
Assume:

• 50 lb/A rate
• Test run-200 ft
• Four runs made
• Application width-12 ft
• 11.5 lb to refill hopper

      Area covered    =  4 x 200 x 12     =     0.22A
                                      43,560

      Application rate =      11.5              =     52.27 lb/A
                                            0.22

8. If application rate is not correct, adjust feed gate opening and recheck.

Band Applicators

1. From the label, determine application rate.
2. From the operator's manual, determine applicator setting and adjust accordingly.
3. Fill hopper half full.
4. Operate applicator until all units are feeding.
5. Stop applicator; remove feed tubes at hopper.
6. Attach paper or plastic bag over hopper openings.
7. Operate applicator over measured distance at the speed equipment will be operated.
8. Weigh and record amount delivered from each hopper. (Be sure all hoppers and all tubes deliver the same amount.)
9. Calculate application rate:

• Area covered in bands (acres) =    number           length of                band
                                                              of bands    x      run (ft)       x       width (ft)
                                                                                           43,560
• Application rate: Rate applied in bands (lb/A)   =  total amount collected (lb)
                                                                                          area covered in bands (acres)

10. If not correct, readjust and recheck.

Calibration for Changing from Broadcast to Band Application. Within a field, the treated area may be only a fraction of the total land area. Calculate application rates for portion of the field that is treated, using the ratio of band width to row spacing, as follows:

   Band width               broadcast                 amount needed
     in inches         x          rate                =               per acre                              
   row spacing              per acre                             of field
      in inches