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Spraying insecticides or fungicides downwards with a knapsack sprayer


This video will show you how to downward spray a pesticide, using water. Click the play button to view the video now or click on the script tab to view the storyboard. To view the video off-line, click the link from the 'download' tab.


This video will show you how to downward spray a pesticide, using water. You will need:

  • your pesticide label
  • your knapsack sprayer and nozzle
  • clean water
  • canes or sticks and



personal protective equipment as directed by your pesticide label.





From the pesticide label you will know:

  • the amount of pesticide to be applied
  • the water volume rate to use and
  • the type of nozzle advised



You will have used some of this information to find out the size of nozzle you need and so will now also know your:

  • row or swath width
  • your comfortable spraying speed, the
  • nozzle flow rate and the
  • pressure of the knapsack sprayer



In this demonstration, the label advises us to use a hollow cone nozzle to spray smaller, ‘Fine’ drops and we will use 200 ml of a contact insecticide in 400 litres of water to control the pest.





We have calculated that the nozzle size we need has a flow rate of 1.2 litres/minute. The swath width produced by the nozzle is 0.5 metres.





The sprayer will be pressurised at 2.3 bar. Our operator will be spraying with the nozzle 50 cm from the foliage at a speed of 1 metre/second or 3.6 km/hour





When practicing spraying, only use clean water.






And wear your PPE so that you get used to wearing it and can adjust it so that you are comfortable. When spraying downwards, pull your coverall/long sleeve out and over the glove so that the glove is worn inside the sleeve. Some pesticide labels will permit the use of long sleeved shirt and trousers as dedicated PPE; a better option is to wear a coverall. Always wash PPE separately.




This knapsack has already been cleaned, checked, and calibrated. If you are not familiar with how to do this, please have a look at our separate videos.





As you approach the start point of the row to be sprayed, walk at your preferred spraying speed – the speed which you used to calibrate your sprayer. As you reach your start point, start spraying with your nozzle 50 cms from the foliage. Walk slightly to one side of the spraying nozzle to avoid contact with the sprayed vegetation.





If you are spraying a band/row, spray only the target surfaces. For instance, adjust your swath width so that you only spray the crop row or the row of vegetables. If possible spray with the wind at your back, blowing from you towards the nozzle. Monitor your spraying pressure and keep your spraying speed constant.





Constantly check that your nozzle is producing the right spray pattern and drop size. Check that the spray is reaching the target surfaces. Avoid spraying too much pesticide so that the drops run-off the leaves.





This is too much.






Check that spray is reaching the leaves of the potato canopy that are lower down as well as those at the top of the canopy. Contact insecticides and fungicides will only control the pest where the spray has made direct contact with the pest, so check that every leaf and stem that is sprayed has a cover of drops over the entire surface. Contact herbicides also need an even coverage over all of the weed





You can use the same techniques for the spraying of systemic herbicides. However there is an opportunity with all systemic pesticides to use larger drops rather than the smaller sizes. The spraying of larger drops of systemic sprays will be safer for you as you are less likely to inhale the droplets and safer for the environment as larger droplets are less likely to drift.





When air is coming out of the nozzle and the spray liquid is all used,






place a stick at this point. This will mark the point where spraying will continue with the next load.





Leave a small un-sprayed area which can be sprayed later with the water used to clean the inside of the sprayer.