Step 5 of 6 - calibrating your knapsack sprayer for pesticide dose and spray mix/water volume
This video will demonstrate maintaining spraying speed, the nozzle distance and knapsack sprayer pressure. Click the play button to view the video now or to view the video off-line, click the link from the 'download' tab.
Next practice maintaining your spraying speed, the nozzle height and sprayer pressure so that you achieve the right swath width and spray distribution and can complete the calibration.
Your spraying speed is the speed at which you move the nozzle over the treatment surface to achieve the correct application rate. It may vary under different conditions so always check your spraying speed each time you spray.
You will have established your spraying speed when finding out the size of nozzle that you need. To practice it again now and to complete calibration, measure and mark an area of 25 square meters.
In this case, as we are using a single nozzle producing a 0.75 m swath, and as it is easiest to just walk in a straight line, our area will be 0.75 meters wide and 33.3 metres long, to give us our required area of 25 square meters.
With your knapsack sprayer on your back and half full with water, time how long it takes you to walk and spray that 25 square meters at your comfortable spraying speed, with the nozzle 50 cm from the target surface.
In this demonstration, it has taken 55 seconds for our operator to walk 33.3 meters, very close to 2.4 km/hour or 0.67 m/second required. But, to precisely apply 200 liters/hectare (as needed for this spraying task), he will need to very slightly slow his speed down to 50 seconds when spraying this 33.3 meter length.
Now he is spraying at the speed that will apply 200 liters/hectare (as required for this demonstration).
Spraying too fast introduces many poor practices; the operator will apply too little pesticide and it is very likely that the spray deposits will not be uniform. Also the knapsack sprayer may not be stable on the operator’s back increasing the likelihood that the operator will stumble or fall. Spraying speeds that are too slow will mean that it takes a much longer time to spray.