Irrigation districts commonly use herbicides for vegetation control on levees and ditches. When applied correctly, recommended herbicides do not typically injure people, animals, or crops. However, if improperly applied, herbicides can be dangerous and costly.

Application Risks

If improperly applied, herbicides can travel to non-target areas such as nearby homes, playgrounds, waterbodies, and fields, causing contamination, injury, or other damages. Two critical application risks are drift and runoff as herbicides can travel via air and water.

Spray drift occurs when herbicides move through the air. This can be in the form of droplets, particles (fine dust), or vapors, and can occur during or soon after application. Small spray droplets are most susceptible to drift during periods of high wind. Additionally, some herbicides evaporate as temperatures increase and can result in vapor drift.

In addition to water contamination due to drift over water bodies, contamination of groundwater and surface water can occur due to surface runoff and leaching of herbicides. Spills or leaks, overwatering treated areas, improper disposal of herbicide containers, and rinsing equipment near drainage areas can all contribute to water contamination.

Application Considerations

Consider the following application recommendations to reduce the risks of runoff and spray drift.[1]

• Only apply the herbicide directly to the treatment area.
• Be mindful of the location of storm drains, drainage ditches, gutters, or surface waters during application.
• Apply during calm weather conditions, when rain is not predicted for the next 24 hours.
• Measure wind speed and direction before, during, and after application (wind speeds of 3 to 7 mph are preferable[2]).
• Do not apply herbicides during a temperature inversion (when warm air rises above cool air, typically from dusk to dawn3).
• Properly calibrate sprayers at recommended rates.
• When calibrating the equipment, check nozzles for blockage or wear which could result in increased or uneven output.
• When applying granular products, sweep any excess product from driveways, sidewalks, streets, or other hard, impervious surfaces back onto the treated area.
• When watering treated areas, refer to the watering instructions on the label, and ensure you do not water the treated area to the point of runoff.
• Rinse application equipment over the treated area to help avoid runoff to water bodies or drainage systems.

Additional Safety Recommendations

Select a method of application that minimizes the risk of the herbicide traveling away from the intended treatment area. Additionally, select a method that minimizes the release of herbicides to the environment and minimizes the risk of contact to the applicator and others that may be in the area during and after application.  

Consider the following safety recommendations when applying herbicides. [i]

• Make sure you are familiar with current federal and state herbicide/pesticide laws and regulations and that the applicator is licensed, where required.
• Avoid drift of spray or dust that may endanger other crops or animals. 
• Never eat, drink, or smoke while applying herbicides.
• Read and follow all manufacturers’ instructions on the label.
• Wear protective clothing and use protective equipment according to the instructions on the label.
• Wash immediately with soap and water if the herbicide spills on skin or clothing.
• Wash pesticide-contaminated clothing separate from other laundry and take care in disposing of the wash water.
• Store herbicides in their original containers, in a locked and correctly marked cabinet or storeroom, and away from food or feed.
• To avoid cross-contamination, do not store herbicides with other pesticides.
• Triple-rinse all empty containers before disposal (verify state/local requirements for recycling/disposal in an approved landfill).
• Record the date, time, location, weather conditions, and amount of each herbicide used.
• If you suspect poisoning, contact your nearest Poison Control Center, hospital emergency room, or physician.

Conclusion

Herbicides may travel from the application area and cause issues such as contamination of water systems and damage to crops. When applying herbicides, it is important to understand the site conditions, such as proximity to water, depth of groundwater, and crops on or near the property. Selecting an application method that minimizes environmental impact is vital. Ensuring proper application of herbicides will help irrigation districts reduce the risks of contamination and other associated dangers.

[1] US Environmental Protection Agency (EPA). (2017). Introduction to pesticide drift. Retrieved from https://www.epa.gov/reducing-pesticide-drift/introduction-pesticide-drift

[1] Dorn, E., Hansen, P., Ogg, C., Bauer, E., & Hygnstrom, J. (2017). 5 Things to know to avoid herbicide drift. University of Nebraska-Lincoln Institute of Agricultural and Natural Resources. Retrieved from https://cropwatch.unl.edu/5-things-know-avoid-herbicide-drift

[1] Lingenfelter, D. (n.d.). Introduction to weeds and herbicides. PennState Extension. Retrieved from https://extension.psu.edu/introduction-to-weeds-and-herbicides#section-31