Herbicide drift refers to the unintended movement of herbicide particles or vapors away from the intended application site to non-target areas. This is a concern in agriculture and landscaping, as it can damage sensitive plants and other organisms. The accidental spread of these chemicals can lead to various issues, impacting both the environment and economic activities.
Understanding How Herbicide Drift Happens
Herbicide drift occurs through two mechanisms: particle drift and vapor drift. Particle drift involves the physical movement of small spray droplets by wind during or shortly after application. Nozzle type, spray pressure, and boom height influence droplet size, with smaller droplets being more susceptible to wind dispersal. Increasing spray pressure can create finer droplets, while lowering boom height can reduce the distance droplets travel horizontally before reaching the ground.
Vapor drift occurs when volatile herbicide formulations turn into a gas after application, moving off-target. This transformation is influenced by environmental temperatures, particularly during temperature inversions, where warm air traps cooler air near the ground. These conditions can hold herbicide vapors close to the surface, allowing them to travel considerable distances. The herbicide’s chemical properties, including its vapor pressure, determine its likelihood of volatilizing.
Environmental conditions play a role in exacerbating both types of drift. Wind speed and direction are direct drivers of particle drift, as stronger winds can carry droplets further from the application zone. Temperature inversions can prevent vertical mixing of air, trapping herbicide particles and vapors and allowing them to move horizontally over long distances. Low humidity can also contribute to drift by causing spray droplets to evaporate more quickly, resulting in smaller, more drift-prone particles.
Impacts of Herbicide Drift
Herbicide drift affects non-target plants. Sensitive crops like soybeans, grapes, and tomatoes are susceptible, often showing symptoms such as leaf curling, discoloration, stunted growth, or plant death. Ornamental plants and native vegetation can also suffer similar damage, diminishing aesthetic value and disrupting local ecosystems. The extent of damage depends on the herbicide type, its concentration, and the sensitivity of the exposed plant species.
Beyond plant damage, herbicide drift can have broader environmental effects. Drift can indirectly contribute to water quality concerns if deposited chemicals are washed into streams or ponds. There are also impacts on non-target organisms, including beneficial insects like pollinators and other wildlife. Effects vary depending on the chemical and exposure level. The disruption of insect populations can have cascading effects on food webs and ecosystem services.
Economically, herbicide drift can result in losses for farmers due to reduced crop yields or destruction of affected crops, necessitating replanting. These financial burdens can be substantial, particularly for specialty crop growers whose products are sensitive to herbicide exposure. Incidents can also lead to legal disputes between affected parties, adding economic strain and potentially souring neighborly relations.
Concerns also extend to human and animal exposure. The severity of symptoms depends on the herbicide, exposure level, and individual sensitivity. Humans can be exposed through direct contact, inhalation of airborne particles or vapors, or by consuming contaminated produce. Pets and livestock can also be exposed by grazing on affected vegetation or through direct contact. Awareness of exposure pathways is important.
Strategies to Reduce Herbicide Drift
Careful applicator practices minimize herbicide drift. Before and during application, check weather conditions, including wind speed, direction, temperature, and humidity. Applying herbicides when wind speeds are low (below 10 miles per hour) reduces off-target movement. Avoiding applications during temperature inversions is also important, as these conditions can trap and transport herbicide vapors over long distances.
Selecting appropriate equipment and formulations also reduces drift. Using low-drift nozzles, which produce larger, heavier droplets less prone to wind dispersal, mitigates particle drift. Maintaining correct spray pressure and setting the boom height at the lowest practical level for uniform coverage minimizes the distance droplets travel. Applicators can also choose less volatile herbicide formulations, which are less likely to convert into vapors after application, especially in warmer temperatures.
Drift reduction adjuvants, substances added to the spray mixture, can also help by modifying droplet characteristics to reduce drift. Establishing buffer zones, untreated areas around sensitive crops, residential properties, or water bodies, provides protection by creating a physical barrier. These zones act as a safety margin, allowing stray herbicide particles to settle before reaching vulnerable areas.
Adhering to herbicide product labels is a fundamental practice for drift mitigation. These labels contain specific instructions regarding application rates, environmental conditions, and equipment settings designed to minimize off-target movement. Following these guidelines is a regulatory requirement and an effective means of preventing drift incidents.
What to Do if Herbicide Drift Occurs
If you suspect your property or plants have been affected by herbicide drift, documenting the incident thoroughly is a sensible first step. Take clear photos and videos of the affected plants, showing visible symptoms like leaf curling, discoloration, or stunted growth. Note the date and time you first observed the damage, the specific location, and any relevant weather conditions at the time of the suspected application. This detailed record will be helpful in any subsequent actions.
If the source of the application is known, communicating directly with the responsible party can sometimes resolve the issue amicably. Sharing observations and documentation might lead to a better understanding of the incident and potential solutions. Open communication can often prevent further complications and foster better relationships within the community.
If direct communication is not possible or does not resolve the situation, report the incident to the appropriate authorities. State agricultural departments or pesticide regulatory agencies are responsible for investigating herbicide drift complaints. The Environmental Protection Agency (EPA) also oversees pesticide use and can provide guidance or direct you to relevant state offices. Providing them with your documentation will assist their investigation.
As a safety precaution, avoid direct contact with affected areas and refrain from consuming produce from plants that show signs of contamination. If consumption cannot be avoided, washing produce thoroughly before eating is recommended. These measures help minimize potential exposure to herbicide residues.
References
Kansas State University. (n.d.). Understanding Herbicide Drift. [Online]. Available: https://www.bookstore.ksre.ksu.edu/pubs/mf3320.pdf
North Dakota State University. (n.d.). Herbicide Drift and Injury to Plants. [Online]. Available: https://www.ndsu.edu/agriculture/ag-hub/ag-experts/extension-specialists/plant-sciences/weed-science/herbicide-drift-and-injury-plants
University of California Agriculture & Natural Resources. (n.d.). Reducing Herbicide Spray Drift. [Online]. Available: https://anrcatalog.ucanr.edu/pdf/8596.pdf
University of Missouri Extension. (n.d.). What to Do if Herbicide Drift Occurs. [Online]. Available: https://ipm.mo.edu/cropPest/2012/6/What-to-Do-if-Herbicide-Drift-Occurs/