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7 Tips for Reducing Spray Drift

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When spraying herbicides and insecticides, you don't want the drift catching on your plants. Here are 7 tips for reducing spray drift.

Spray drift isn't just a health concern - it's a legal issue.

If you're not in proper control of your pesticide spray, you could have to answer to the Environmental Protection Agency (EPA). As the primary organization responsible for regulating pesticides in the United States, the EPA is serious in ensuring spray drift is minimized as much as possible.

And it's clear to see why it's a big concern for them - the EPA estimates that up to 70 million pounds of pesticides are lost to drift each year.

There's also the legality of being financially responsible for your neighbor's crops or plants if they are damaged by your spray drift. And that's not a cost I'm sure you want to cover.

Keeping pesticide contained within your intended area is a major concern for most farmers. Here are some of the negative effects of spray drift:

  • Reduced efficacy on intended crops - every droplet that drifts mean less spray is being deposited on the target
  • Financial loss
  • Health risks to humans in nearby homes and schools
  • Health risks to non-target organisms, including wild and domestic animals
  • Damage to nearby property
  • Damage to adjacent farms
  • Contamination of household and farm water supplies, including tank water

7 Tips for Reducing Spray Drift

  1. It ain't easy when it's breezy

    Spraying pesticides during heavy winds are bound to result in spray drift. Air movement will almost always result in some spray being carried outside your target area. The greater the wind speeds, the greater the amount of spray drift.

    Aim to only spray when wind velocities are less than 10 mph, and when the wind direction is away from vulnerable crops. In general, winds are calmer early in the morning or late in the evening.

    Using a wind meter is a great way to check the speed of the wind, the temperature, and even humidity and heat stress information. High temperatures and low relative humidity cause the pesticide droplets to become smaller due to evaporation.

    Another weather condition to be aware of it rain. Applying pesticide when rain is not predicted for the next 24 hours will help to ensure that wind or rain does not blow or wash pesticide off the treatment area.

  2. Keep it close

    Try to keep your nozzles as close to the target as possible by using lower spray boom heights. The less distance between your nozzle and the target, the faster the liquid will land and therefore be in the air for less time. the less spray drift.

    For a horizontal boom sprayer such as a herbicide sprayer, try to lower the boom as low as practically possible. A good general rule to remember is that the boom should be twice as high as the nozzle spacing. If you own an airblast sprayer, this could mean considering a tower sprayer.

    Aim to use nozzles that have a spray angle of 110 degrees. This will allow the boom to be lowered more than nozzles with lesser angles but will maintain the spray pattern and proper overlap. In general, for a boom with 20-inch nozzle spacings, maintain a boom height of 24 inches or less above the crop canopy.

  3. Reduce pressure, reduce droplet size

    The spray tips & nozzles you use for spraying can produce different droplet sizes at different pressures. The pesticide spray mixture is broken into spray particles or droplets of various sizes.

    According to the Pesticide Environmental Stewardship, spray droplets smaller than 150 microns are most prone to drift. As they do not have enough weight to overcome air resistance, they're more likely to float in wind currents.

    When the size of the spray droplets is reduced, their numbers increase and they fall more slowly than large droplets. That means the potential for drift increases.

    Lowering the pressure of your spray allows for larger droplet sizes, and therefore less drift. The characteristics of the nozzle tip (type, fan angle, orifice size, etc.) is a major factor in the pressure of your spray.

  4. Use spray thickeners/ drift retardants

    These types of solutions are normally a type of long-chain polymer or gum that increases the viscosity of the spray mixture.

    Adding these types of solutions to your spray liquid can make your spray thicker. This will dramatically change the flow rate and droplet size for more effective spraying.

    However, don't use spray thickeners or drift retardants at the same time as air induction nozzles. This can create clogging.

  5. Slow and steady wins

    The faster you are driving while spraying, the more your spray will drift. Fast moving sprayers may cause the boom to bounce and spray droplets high into the air, affecting a larger space than the intended area.

    Aim to reduce your sprayer ground speeds to less than 10mph.

  6. Buffer zones

    A buffer zone is an area left designated as a no-spray zone between a sensitive area and a crop being sprayed.

    If there are vulnerable crops close to your targeted crops, buffer zones are a great idea. Always be aware of labeled buffer zones near you.

    The required distance of a buffer zone may continually be different each day, depending on certain factors such as:

    - The product you are using - some legally require a certain buffer zone to be present in order to use the product
    - The wind direction and speed on the day
    - The nature of the sensitive area you are trying to protect. Different distances may be required for crops compared to residential housing
    - The type of application equipment you are using - a boom spray that produces large, coarse droplets is less prone to drift than a mister producing fine, smaller droplets

  7. Use air-curtains or air-shielded booms

    Air-curtain or air-shield booms are designed with an external blower fan system. The blower creates a high velocity of air that directs the spray towards the target.

    Some sprayers provide a shield in front or behind the nozzles. This will prevent the spray from being blown off-target by blocking any wind blowing towards it.