Three Ways to Reduce Off-Target Drift

Dr. Jason S.T. Deveau, OMAF & MRA; Tara Wiedeman, Summer Research Student, OMAF & MRA

There is no excuse for off-target herbicide drift because the spray operator can reduce the potential impact using these methods:

  • Apparent wind speed (i.e. the sum of wind speed and travel speed)
  • Boom height (i.e. release height)
  • Droplet size (i.e. nozzle spray quality)

We recently conducted a short demonstration to show the impact of these factors on spray drift using a backpack sprayer, a variable-rate fan and some water-sensitive paper positioned every 1.5 metres downwind.

Wind Speed

Spray operators know they should not spray when the air is calm or when the wind is too high, but they often forget that the nozzles experience “apparent wind speed” which means driving 10 km h into a 10 kmh headwind is essentially spraying in a 20 kmh wind. Here are the results of spraying with a medium spray quality in 10 kmh and 15 kmh wind:

The water-sensitive papers and graph indicate that there is more downwind drift in higher winds.
The water-sensitive papers and graph indicate that there is more downwind drift in higher winds.

Boom Height

Spray operators raise their booms to ensure their nozzles clear the crops, but this contributes to off target drift and greatly reduces coverage – particularly when using twin-fan style tips. Dr. Tom Wolf explains how to set your boom height here: http://www.realagriculture.com/2014/04/spray-tips-tom-wolf-ep-5/. Here are the results of spraying with a medium spray quality in a 10 kmh wind at 50 cm and 100 cm from the ground:

The water-sensitive papers and graph indicate that downwind drift increases as the boom gets higher.
The water-sensitive papers and graph indicate that downwind drift increases as the boom gets higher.

 

 

Droplet Size

The coarser the spray quality, the less likely the spray will drift off target. Remember that shifting to larger droplets means fewer droplets, so application volumes may have to increase to compensate for potentially reduced coverage. Here are the results of spraying with a medium spray quality versus spraying with an extremely coarse spray quality:

The water-sensitive papers and graph indicate that there is more downwind drift from smaller droplets.
The water-sensitive papers and graph indicate that there is more downwind drift from smaller droplets.

 

Take-Home

So even when the spray window is small and the spray has to go on, take a moment to drop the boom, use a coarser droplet size and if it’s too windy, don’t spray.

See the entire spray demonstration on Real Agriculture:

http://www.realagriculture.com/2014/05/three-tips-managing-spray-drift/

For more information about pesticide drift, go to:

http://sprayers101.ca/additional-information/spray-drift/

Always follow the pesticide label and STOP DRIFT BEFORE IT STARTS!

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