Top tips and new tools for aerial herbicide application
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Aerial herbicide application provides an efficient way to treat large areas of rangeland, pasture and non-crop areas. However, if not done correctly, the potential for damage to nearby desirable plants can be significant. For land managers seeking to use aerial application for weed control, the combination of application best practices and new, nonvolatile herbicides can offer a safer way forward.
Physical drift vs. vapor drift
Physical drift and vapor drift both need to be considered when planning for aerial herbicide application. Although often conflated, the two are distinct issues.1
Vapor drift refers to volatility, which is the ability of herbicides to vaporize and transform from liquid to a gas, increasing the potential for off-target movement. This is a common problem with ester-based herbicides, which are formed with an alcohol, making it easier for absorption through plant leaves.2
Physical drift refers to the airborne movement of herbicides in a non-gaseous form from the target location into adjacent areas.1 Off-target movement can occur in vapor, droplets, mists, aerosols, dusts or other types of fine spray particles. It can occur with any type of herbicide, but steps can be taken to prevent or reduce it.
Aerial application best practices
Prepare in advance:
- Assess the surrounding region for potential risks, including physical hazards for aircraft like electrical wires and the presence of waterways and susceptible plants in adjacent areas.3
- Scout the location for application and record the distance from the site to farms, ranches and operations with animals or livestock.3 Also check proximity to honeybee hives and commercial pollinating insects and know about current cultural practices occurring at the site or other adjacent agricultural areas.
- Check and comply with state regulations regarding aerial application, and ensure that neighbors are properly notified and signage is posted around the area to be sprayed.3
Understand height and wind influence on drift:
- Managing and avoiding spray drift during application is the applicator’s responsibility. Factors that can increase the risk of pesticide drift include wind direction, application height and wind speed.
- Check flight paths to ensure they account for buffer zones, terrain and wind patterns.
- Evaluate techniques that may help minimize off-target herbicide movement, including boom shut-offs, crosswind applications, application height and buffer zones.3
Know best practices for product application:
- Knowing more about the herbicide will provide information about how it handles in different temperatures and humidity situations.
- Make sure the herbicide is applied at the correct rate. Using too little may not provide effective control and can spur development of resistance.4
- Apply herbicides at a time when they are most effective against specific weed challenges.4
- In hot or dry conditions, be aware that using larger droplets may help prevent product evaporation.
Account for wind direction and temperature inversions:
- Use a smoke generator to determine if the spray has the potential to drift based on wind conditions — and identify positive air movement away from critical areas. Smoke systems also can be used to identity temperature inversion situations.3
- Temperature inversions may happen when there is increasing temperature as altitude is gained. This can occur at night if there is limited cloud cover and little wind. The situation may be indicated by ground fog or the movement of smoke provided by a ground-based source or aircraft smoke generator. Smoke that moves laterally and remains in a concentrated cloud indicates an inversion is present. Alternatively, smoke that rapidly dissipates and moves upward signals vertical air mixing.
Use properly aligned spraying equipment:
- Remember to account for boom length — it cannot exceed 75% of the wingspan when using airplane deployment.3 In helicopters, the boom should not exceed 85% of the rotor blade diameter.
- The size, type and direction of the nozzles used help determine droplet size and can be altered to help mitigate drift risk.
- Consider use of low-drift nozzles and remember to select the correct shape of nozzle — straight stream and fan pattern nozzles have tested best in drift studies.
- Using larger droplets is one way to reduce the potential for spray drift. However, while increasing droplet size reduces the potential for drift to occur, the risk of drift remains higher if applications are made incorrectly or when unfavorable environmental conditions are occurring.
Monitor application and dispersal and keep records:
- Swath-marking tools like flags, smoke or GPS aid application and help reduce the possibility of off-target drift. Monitor application to check for uniform dispersal.3
- If the herbicide needs to be mixed, make sure that only approved products and methods are used.4 Different products may need different clean-out procedures to prevent equipment from being clogged or damaged.3
- Remember to collect documentation records from your applicator following spraying to comply with federal regulation. Records should be kept for at least two years. Additional state-level requirements also may be in place.3
Adding new herbicides to the aerial toolkit
Another decision that managers can make to reduce the potential for off-target movement during the aerial application is to select a product that has low volatility.
New HighNoon® herbicide with Rinskor® active is a nonvolatile herbicide that does not include 2,4‑D or dicamba. Instead, HighNoon contains aminopyralid combined with florpyrauxifen-benzyl, a new class of synthetic auxin chemistry branded as Rinskor active. HighNoon controls more than 140 broadleaf and invasive weeds and it maintains grass safety. HighNoon is not a Restricted Use Pesticide and can be used as an aerially applied herbicide when best practices are followed:
- Do not release spray at a height greater than 10 feet above the vegetative canopy unless a greater application height is necessary for pilot safety. This requirement does not apply to forestry or rights-of-way applications.
- Applicators are required to use a coarse to coarser droplet size (ASABE S572.1).
- The boom length must not exceed 75% of the wingspan for airplanes or 85% of the rotor blade diameter for helicopters.
- Applicators must use 1/2 swath displacement upwind at the downwind edge of the field.
- Nozzles must be oriented so the spray is directed toward the back of the aircraft.
- Do not apply when wind speeds exceed 10 miles per hour at the application site.
- Do not apply during temperature inversions.
Making the most of aerial application
There can be several advantages to the aerial application of herbicides, such as addressing wide-spread or ranging weed challenges. Although off-target movement continues to be a consideration when herbicides are applied by air, the proper equipment, products and techniques allow it to be effectively managed.
References:
1 Gratkowski, H. and Stewart, R. “Aerial spray adjuvants for Herbicidal Drift Control.” USDA Forest Service General Technical Report, 1973, https://www.fs.fed.us/pnw/pubs/ pnw_gtr003.pdf.
2 Hager, Aaron. “Formulations of 2,4-D: Acids, Esters, and Amines,” University of Illinois Bulletin, 2007, Vol 7. http://bulletin.ipm.illinois.edu/print.php?id=713.
3 O’Connor-Marer, Patrick. “Aerial Applicator’s Manual: A National Pesticide Applicators Certification study guide.” National Association of State Departments of Agriculture Research Foundation. https://www.agaviation.org/Files/RelatedEntities/Aerial_Applicators_Manual.pdf.
4 “The Top 10 Pesticide Application Mistakes.” Ag Air Update, 2015, https://www.agairupdate.com/the-top-10-pesticide-application-mistakes/. ™
Hay from grass treated with HighNoon™ within the preceding 18 months can only be used on the farm or ranch where the product is applied unless allowed by supplemental labeling. Under normal field conditions, HighNoon is non-volatile. HighNoon has no grazing or haying restrictions for any class of livestock, including lactating dairy cows, horses (including lactating mares) and meat animals prior to slaughter. Label precautions do apply to forage treated with HighNoon and to manure and urine from animals that have consumed treated forage. HighNoon is not registered for sale or use in all states. Contact your state pesticide regulatory agency to determine if a product is registered for sale or use in your state. Always read and follow label directions.
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