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We Catch Your Drift

Warm, windy days have arrived: cottages are open, barbeques are hot and pesticide is drifting in the air. Anything seem out of place in that description? So what are you doing to keep those expensive products on-target and out of the summer breeze?

Drift is the airborne movement of agricultural chemicals onto a non-target area with the risk of injury or damage to humans, plants, animals, environment or property. Every farm should develop spray drift management strategies relevant to their particular circumstances and spray applicators (in-house or commercial applicators) should follow them.

Develop Spray Drift Awareness Zones

Much can be done to mitigate spray drift when planning a new farm by identifying where pesticide use may conflict with adjacent land use. Incorporate adequate separation between cropped areas and so-called "sensitive areas". For established plantings, create a map of the crop and surround it with a 1 km spray drift awareness zone. Survey the zone and identify any sensitive areas that could be affected by spraying: e.g. neighbouring sensitive crops, native flora and fauna, waterways and wetlands, bees and sites of human habitation or activity (see Figure 1). An operational plan should be prepared for all routine spraying that includes site-specific instructions for each sensitive area falling in the awareness zone. Note that droplets can be carried well beyond 1 kilometre, depending on the conditions, even long after the application.

Fig 1 - Establishing a 1.0 kilometre Awareness Zone

Observe Buffer Zones and Establish Vegetative Barriers

Pesticide labels specify downwind buffer zones to protect sensitive areas. The distance will depend on the toxicity of the product, the potential exposure to non-target organisms, the weather and the application method. At the time of this article, a new approach to determining buffer zone width is being developed by the Pest Management Regulatory Agency (PMRA). It uses a series of multipliers that increase or decrease the zone based on the type of sprayer, wind speed, and the nature of sensitive area, such as the depth of any permanent aquatic area. Until this new method is introduced, follow the label and consider planting vegetative barriers (aka wind breaks or buffer strips) along the downwind side of the crop. It can be a tree or shrub line surrounded by tall grass and should be more than one row of vegetation. Studies have shown that a density of about 50% with a minimum height of 1.5 times the release height of the spray can potentially reduce drift by 45 to 90% (See Figure 2). For more information see the Best Management Practices publication entitled "Buffer Strips".

Fig 2 - Plant Downwind Vegetative Barriers

Watch the Weather and Employ Drift Mitigating Technology

Operators should spray only when temperatures are low and relative humidity is relatively high. This reduces the chance of drift due to temperature inversions or evaporation and it increases target deposition and coverage. In general, only spray when relative humidity is between 40 and 80% and air temperature is less than 25°C.

Wind speed affects the distance that a droplet will travel before deposition. Only spray when wind direction is consistent and between 2-15 km/h, or as indicated on the product label. Table 1 matches the visible signs of wind to the potential for drift and advises whether or not to spray. Cut out the scale shown in Figure 3 and tape it up in the spray cab for quick and easy reference. Applicators can operate in the higher end of this range by using:

• drift-mitigating nozzles,
  
• larger droplets,
  
• slower forward speeds,
  
• by reducing the distance-to-target, and
  
• by using shrouds or deflectors

Fig 3 - Drift Scale Cut-out

Table 1: Wind Conditions and Spraying Recommendations

Communication

Last, but not least, communicate with your neighbours. Many drift incidents can be avoided or greatly reduced if neighbours and contractors are advised and consulted prior to application. This can be verbal communication or written depending on the situation. Come to a mutually agreeable solution, perhaps sharing the responsibility for buffer zones or wind breaks.

Mitigating drift is the responsibility of all applicators. I hope you catch my drift so no one catches yours.