Reducing Pesticide Spray Drift: 5 Key Aspects

What is pesticide spray drift?

Pesticide spray drift is the movement of a pesticide through the air away from the intended target.

When spraying terrestrial weeds and aquatic weeds that are not submerged, the spray is expected to reach specific targets and remain there. When a pesticide goes where it is not needed, it may endanger human health, injure desirable plants and animals, and contaminate the environment.

When spraying submerged aquatic weeds, the spray is intended to reach and stay on specific targets. However, within aquatic systems, the spray solution is subjected to waves, inflow, outflow, and currents which can cause pesticides to drift and impact the control of aquatic weeds.

Pesticide spray drift was originally thought to occur only when applications were not done properly. It is now widely accepted that even when pesticides are applied properly, spray drift can occur.

What causes spray to drift?

In terrestrial systems, factors like weather, the application site, and type of pesticide formulation used can determine the potential ofpesticide spray to drift off-target.

In aquatic systems, underwater currents will determine the potential of pesticide spray to drift off-target.

However, the most critical determinant whether or not pesticide spray drift will occur is the decision by the applicator. The applicator must be trained and fully aware of the potential for pesticide spray to occur even when pesticides have been applied properly and according to label instructions.

Why ispesticide spray drift a concern?

1. Pesticides are expensive and prevention of drift is a cost saving measure for this pest management tool.
2. Pesticides are undesirable in the environment for several reasons, including:
   1. Unacceptable smell, which can be offensive to some people.
   2. Danger to wildlife and other non-targets.
   3. Contamination of groundwater and freshwater resources used for human consumption.
   4. Being hazardous to human health.
3. Pesticides that drift can damage sensitive crops in surrounding areas leading to potential lawsuits. Therefore, a greater awareness of pesticides in the environment has caused spray drift management to become every applicator’s business.

5 Key aspects to reducing the potential for pesticide spray drift

To reduce the potential for pesticide spray drift, pesticide applicators must pay attention to five key aspects. 

1. Spray characteristics -Large-sizedspray droplets are less likely to drift off-target compared with small-sized spray droplets.
2. Choice of adjuvants – An ideal drift control adjuvant:

1. Increases the viscosity of spray droplets which makes them heavier and less likely to drift off-target.
2. Has nonionic properties which allows it to be mixed with a variety of pesticides and fertilizers.
3. May include additional properties, such as:
4. Wetting ability – which helps reduce the surface tension of spray droplets and increases spray coverage on plant leaf surfaces.
5. Penetrating ability – which improves the ability of the pesticide to penetrate the cuticle of leaf surfaces and be absorbed.

• Sticking ability – which causes the spray droplets to adhere to the target surface, decreasing potential for wash-off during rainfall, and enhancing retention of the spray.

1. Sinking ability – which helps develop viscous droplets which enable spray to reach submerged weeds at the bottom of an aquatic system.
2. Examples of drift-reducing spray adjuvants from Brewer International.
   1. I’vod™ – Nonionic drift control, penetrating, and sticking agent.
   2. Polyan™ – Nonionic drift control and sinking agent.

• Poly Control 2™ – Nonionic drift control and sticking agent.
  • When adjuvants are used, read the label!
    • The label is the law.
    • For the best outcome, read and follow all recommended instructions on pesticide and adjuvant labels.

3. Equipment and application techniques:

1. 1. In terrestrial systems, drift-reducing nozzles, such as air induction nozzles, are designed to produce large, air-filled coarse droplets which substantially reduce the risk of spray drift.
   2. In aquatic systems, subsurface pesticide injection techniques specifically designed for managing submerged weeds in aquatic systems, allow herbicide to be placed near the submerged aquatic weed thereby reducing the risk of spray drift.
2. Weather conditions at the time of application:
   1. In terrestrial systems, air movement, temperature, and humidity are factors that need to be accounted for when applying herbicides to control weeds and aquatic plants that are not submersed.
   2. In aquatic systems, wind, waves, inflow, outflow, and currents can dilute herbicides and impact the control of aquatic weeds.
3. Operator care, attitude, and skill:
   1. Custom and private applicators need to be knowledgeable of:

1. The latest technologies and techniques that help reduce spray drift.
2. Current state and federal government laws governing pesticide spray application as they relate to spray drift.

1. 1. Preventing harmful exposure to people or property requires the applicators to evaluate:

1. Their equipment.
2. The weather.

• The site to be treated.

1. The surrounding area.

Further Reading

• I’Vod – A Superior Spray Drift Control Adjuvant

References

• Bohmont, B.L. 2007. The Standard Pesticide User’s Guide – 7^th Pearson Prentice Hall.
• United States Environmental Protection Agency (US EPA). Introduction to Pesticide Drift. https://www.epa.gov/reducing-pesticide-drift/introduction-pesticide-drift. Accessed, May 27, 2022.