March 15, 2011
By Dr. Jason S.T. Deveau
Application technology specialist, OMAFRA

It’s time to consider making changes for this year’s spraying season. Ask yourself a few questions:
  • Do you want to keep more of your product on target?
  • Do you want to extend your spray window (a little)?
  • Do you want to improve the overall effectiveness of your applications?
  • Do you want to reduce the risk of off-target deposition?
Of course you do!

That’s why you need to make adjustments to your spray equipment and reduce the potential for pesticide drift. Spray drift is everyone’s responsibility. Extremely low, and often invisible, amounts of spray drift can be very damaging, even long after the application.

While there are many types of agricultural sprayers used for ground application of pesticides, the two most often associated with spray drift are the airblast sprayers (including cannon sprayers) and the boom sprayers (typically horizontal).

Generally, the goal is to produce a coarser spray quality and bring the nozzle as close to the target as possible, without compromising coverage, or spray quality. There are a variety of ways to modify your sprayer to accomplish this.

For airblast sprayers the potential for drift can be reduced by:
  • adjusting fan settings to produce the minimal effective air speed throughout the season. High fan speeds early in the season are rarely appropriate
  • increasing droplet size by using lower pressures (within the nozzle manufacturer’s ratings), air-induction nozzles or disc-core or disc-whirl nozzles that produce a coarser spray quality
  • using deflectors to channel air into, not over or under, the target
  • using towers to reduce distance-to-target and direct air into the target. Be careful not to get any closer than 50 cm
  • using foliage sensors that turn boom sections on and off to match the size and shape of the canopy
  • switching to a tangential, recycling, multi-duct, or multi-fan sprayer, all of which reduce off-target deposition. Many of these sprayers are rare in Ontario, but they are available. Ask your local retailer for more information. Many eventually pay for themselves in saved pesticide.
For horizontal boom sprayers the potential for drift can be reduced by:
  • maintaining a minimal effective boom height
  • using low-drift nozzles, such as air-induction, drift-guard, turbo tee jet, etc.
  • using drop-arms to bring nozzles closer to the target
  • using the appropriate spray angle. Wider spray angle nozzles (e.g. 110°) create smaller droplets than nozzles with narrower spray angles (e.g. 80°). Although smaller droplets generally increase the chance of drift and reduce penetration in dense canopies, the wider angle nozzles allow the boom to lie closer to the target
  • using air-assist to direct spray into the canopy
  • using shrouds to create physical barriers to drift
Be aware that the equipment described here can reduce, but does not eliminate pesticide drift. Spraying in bad weather and not accounting for the nature of the target increases the potential for drift.

Even with the best equipment, weather plays a big role in increasing or decreasing the potential for pesticide drift. Check out OMAFRA factsheet 09-037W How Weather Conditions Affect Spray Application.

If you’d like to know more about spray drift, methods for preventing it and what to do if you suspect drift damage, keep an eye out for a new OMAFRA Factsheet on Pesticide Drift – it should be available before next year’s spraying season.