Pesticide spray drift is the aerial movement, and unintentional deposit, of pesticide outside the target area. Aside from being illegal, there are a lot of compelling reasons for avoiding it:
- Every droplet that drifts means there is less spray being deposited on the target, resulting in reduced efficacy.
- Drift can be measured in financial loss associated with wasted pesticide, wasted time and reduced crop quality/quantity. Plus, if an application is unsuccessful, the operator may have to re-apply, incurring further cost.
- Certainly not least, pesticide drift increases any risk of damage to human health, susceptible plants (e.g. adjacent crops), non-target organisms (e.g. wild and domestic animals, pollinating insects, etc.), the environment, and property.
We’ll limit this discussion to two forms of pesticide drift: Particle Drift and Vapour Drift. There are situations where the two definitions can overlap, but for our purposes:
Particle Drift is the off-target movement of pesticide droplets (or solid particles). This occurs at the time of application, and while it is generally on a scale of tens-of-metres, temperature inversions can carry it much farther.
Vapour Drift is the off-target movement of pesticide vapours. This generally occurs in hot, dry conditions many hours after the application and is exacerbated if the pesticide is volatile. If vapour gets caught up in a light breeze, moves downhill during a temperature inversion, or is redistributed in precipitation, movement is can be on a scale of kilometres.
Drift cannot be entirely eliminated, but sprayer operators can greatly reduce the potential for pesticide drift. Much of what follows relates predominantly to particle drift, but it’s never wrong to follow these best practices. Research and modeling have shown that the three biggest impacts are:
- Wind speed
- Nozzle-to-target distance
- Nozzle size (i.e. median droplet size)
The following factors also affect particle drift:
- High operating pressures reduce median droplet size
- High ground speeds increase drift, especially if driving into the wind (i.e. increased apparent wind speed)
- High temperatures and low relative humidity cause droplets to become smaller due to evaporation
Therefore, the potential for particle drift can be greatly reduced by:
- Reducing the distance between nozzle and target. For a horizontal boom sprayer, such as a herbicide sprayer, that means lowering the boom to the lowest practicable height. A good rule of thumb is that the boom should be 2x as high as the nozzle spacing. For an airblast sprayer, that might mean considering a tower sprayer.
- Using the coarsest effective droplet size, generally achieved through the use of lower pressure combined with higher-rate nozzles, or air induction nozzles at rates slightly higher than conventional hollow cones.
- Observing labelled buffer zones and recommended sprayer settings. In Canada, using optimal sprayer settings in the right environmental conditions may reward the sprayer operator with buffer-zone reductions.
- Spraying when wind speeds are light to moderate and moving away from any nearby sensitive crop, landscape or environmental areas. Planting windbreaks can help manage wind.
- Changing sprayer settings if the wind increases during spraying or halting the job until conditions improve.
Anyone using pesticides is responsible for their safe application. For example, the Ontario Pesticides Act requires that licensed spray applicators carry a specialized liability insurance policy that provides appropriate coverage for their business. Operators who work on a “for hire” basis (e.g. a licensed spray applicator) or away from their own farm operation will need additional coverage. Where drift damages adjacent crops, insurance adjustors generally ask the following questions:
- Was the damage to the applicator’s own crop? If so, it is unlikely that there will be coverage under any insurance policy.
- Was the damage to a neighbour’s property? If so, the applicator’s liability policy may respond.
- Was the product being applied according to label directions?
If you suspect your crops or property have been damaged by pesticide drift, follow these steps (The contact info is specific to Ontario, so substitute your local authorities):
- Diagnose the problem: many other factors can cause symptoms that appear to be herbicide drift. Look for evidence of weed damage, damage patterns and evidence of nearby spray application.
- Contact the appropriate people: Talk to your neighbour or the sprayer operator to find out what was sprayed, when it was applied, (and who did the application).
- Contact your regional Ministry of the Environment office – MOE officers can do a site visit, take samples of tissue and soil, and have them analyzed for the suspect herbicides. Herbicide residues degrade very quickly, so sampling must occur as soon as possible. In Ontario, contact the nearest regional MOE district office or call the Spills Action Centre at toll free: 1-800-268-6060. (Ministry locations are available at www.ontario.ca/environment or in the Blue Pages of the telephone directory).Where appropriate, the offending applicator may face charges under the Pesticide Act.
- Contact your property and crop insurance insurance adjustors, and advise the applicator to contact theirs.
- Document all details of the problem: This includes your spray records, weather data, photographs with times and locations.
- Document loss: Find a similar planting – same age, cultivar, rootstock, etc. At harvest time, you will need to document yields and quality from the damaged area, and from an undamaged area. For perennial crops like vineyards, orchards, asparagus, berries, etc., it will be necessary to document the effects for several years after the damage occurred. Be sure to note any impacts on vigour and cold hardiness.
Managing spray drift is everyone’s responsibility. Extremely low, and often invisible, amounts of spray drift can be very damaging; even long after the application.
Equipment to reduce drift
For airblast sprayers, the potential for drift can be reduced by:
- Adjusting fan settings to produce the minimal effective air speed throughout the season.
- Increasing droplet size by using lower pressures, air induction nozzles or disc & core (or disc & whirl) nozzles that produce a coarser median droplet size. As the median droplet size is increased, be careful to ensure there are enough droplets to achieve sufficient coverage.
- Using air induction nozzles in the highest operable nozzle positions so most spray falls back into the crop.
- 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 or coverage may be compromised.
- Using foliage sensors that turn boom sections on and off to match the size and shape of the canopy.
- Switching to a tangential, recycling, tower or multi-duct sprayer. Many of these sprayers are rare in Ontario, but they are available. Ask your local retailer for more information.
So 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 want to make adjustments to your spray equipment to reduce 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.