Pesticides - Best Practice Guides


Nozzle Selection and Maintainence


Selecting the appropriate nozzle will have implications for product efficacy and the risk of loses both in run-off to the soil and spray drift. Nozzle selection will often involve a compromise between the requirements for efficacy and for good drift control (see Best Practice Guide on Drift Control)


  • Read the product label
    • follow specific advice given
  • Choose an application volume rate
    • low application volumes (<150 l/ha for arable crops) improve work rates and timeliness.
    • high application rates (>150 l/ha for arable crops) are recognised for good coverage of a dense canopy.
  • Choose a forward speed
    • improved vehicle design and better boom suspensions mean that spraying speeds up to 20 km/h may now be possible. higher speeds (12-16 km/h) improve work rates and timeliness.
    • lower speeds 8-12 km/h) are required to give canopy penetration.
  • Choose a spray quality.
    • a fine spray quality will give improved coverage for a given volume rate, reduced canopy penetration and a high risk of drift.
    • a medium spray quality is the default choice.
    • a coarse spray quality will give lower levels of drift and penetration to the base of the canopy.
    • Use very fine or very coarse spray qualities only in exceptional circumstances.
  • Calculate a nozzle flow rate, from
    • Nozzle flowrate (litres/min) = (application rate (l/ha) x speed (km/h) x nozzle spacing (m))/600
  • Choose a nozzle type.
    • Conventional flat fan
    • Conventional hollow cone
    • Air induction flat fan
    • Pre-orifice deflector

See also the HGCA nozzle guide.

Selecting a Nozzle - The Main Steps:

  • Twin-fluid nozzles give a wide range of spray quality and flow rate depending on pressure settings see manufacturers literature.
  • Twin-caps give a relatively fine spray for higher flow rates and a variation of trajectory angle that will improve canopy coverage but reduce penetration.
  • Avoid the use of higher pressures (>4.0 bar) that could cause leaks and component failure.
  • A good boom suspension will enable lower boom heights and wider angle nozzles to be used. The preferred option for drift control, coverage and penetration is to use the lowest practical boom height.
  • Not all combinations of flow rate and spray quality can be achieved with conventional pressure nozzle designs. Wider spray angles and lower flow rate nozzles give finer sprays.
  • Use manufacturers catalogues for final selection. PSD website gives details of LERAP star ratings.
  • Refine your selection adjust forward speed and/or volume rate to give final selection.


  • Check all nozzles on the boom are the same size, type and angle colour coding will help check size (flow rate).
  • Visually check spray pattern change any nozzles giving a disturbed pattern.
  • Check flow rates at the selected pressure using a jug test on a sample of nozzles
  • are they the same?
  • Do they agree with manufacturers data?


  • Check all nozzle mountings for leaks, security and direction.
  • Measure flow rates (jug test) replace all nozzles on a boom if flow rates exceed manufacturers quoted value by more than 10%.
  • Visually check spray patterns replace nozzles having a damaged pattern.
  • Clean and unblock any blocked or partially blocked nozzles using a brush. Replace nozzles that cannot be cleaned and unblocked easily.

Avoiding Drift

  • Apply in ideal spraying conditions Force 2 light breeze (3.2-6.5 km/hour)
  • Select drift reducing nozzles
  • Ensure correct boom height above crop; keep as low as practical
  • Ensure correct forward speed and pressure. More advice can be found in the CPA Best Practice Guide "Avoiding Drift".

HGCA Nozzle selection chart.

This guide was produced by the Crop Protection Association.

April 2005

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