The Dos and Don’ts of Safe and Effective Herbicide Application: Part 4

Disclaimer: This series is informational only and does not act as a substitute for the Indiana Pesticide Applicators Certification. For more information on obtaining an Indianan herbicide Applicator License please see the Office of the Indiana State Chemist. 

Click Here to Read Part 1
Click Here to Read Part 2
Click Here to Read Part 3
 
Pesticide and herbicide applications play an important role in managing pests and maintaining plant health. However, improper application can result in off-target impacts—where chemicals drift or move to unintended areas, harming non-target plants, wildlife, and even human health. By using safe application methods and effective spray techniques, we can minimize these risks while achieving optimal results. The following guidelines and considerations will help make your next herbicide application a success.
 
Choose the Right Equipment

Nozzle Selection – Sprayer nozzles can produce different spray shapes and characteristics.  Nozzles that produce larger droplets are less likely to drift than those that produce finer droplets. Drift-reducing nozzles are designed specifically to help minimize off-target movement.

Pressure Settings - Keep your sprayer at the lowest pressure that still provides good coverage. Higher pressure can create fine mist droplets that are more susceptible to drifting in the wind.

Application Method - Your application methods may vary depending on factors such as environmental conditions, target species, plant density, proximity to water or sensitive habitats, and the size of the target area. This variation can also affect the equipment required. Methods like foliar treatment with a backpack sprayer, cut-stump application, hand-wicking, high-pressure spraying, and others each have specific tools, skills, and approaches. For assistance in determining the most appropriate method for your needs, consider reaching out to your local Soil and Water Conservation District (SWCD) or Extension representative for a site-specific recommendation.

Applicator Type - Herbicide applicators come in many shapes and sizes, from Buckthorn Blasters which gently paint herbicide onto cut stems and small surfaces to hand-held sprayers, backpack sprayers, or high pressure power sprayers that can carry many gallons of herbicide and dispense them in short order. Understanding the scope of work, your skillset, and target species is essential to determining which sprayer you should use. If you are doing a cut-stump herbicide treatment on a relatively small area of land (less than an acre), consider using a buckthorn blaster or hand-held sprayer. For larger properties or for a more versatile approach a backpack sprayer might be a good investment, and in extreme cases of widespread dense invasive coverage it may be useful to buy or rent a high-pressure power sprayer. These are just a few of the more common herbicide applicator types and there are a wide variety of options available for specialized uses - to learn more about what tools are appropriate for your property, contact your local SWCD or Extension office. 

Hand-Pump sprayers are highly versatile when relatively little herbicide is being applied. They can be used for cut-stump treatments, foliar spraying, and basal bark applications.

Backpack Sprayers can be hand-pump operated or utilize gas or electric motors to generate pressure. They are the tool of choice for many people with larger projects or operating professionally.

Timing Your Application

Weather Conditions - Avoid spraying in windy conditions, as wind can carry droplets away from the target area. Ideal wind speeds for spraying are typically between 3-10 mph in open areas or areas with sensitive environments. Higher winds of 10-15 mph can be acceptable, especially if spraying in a more sheltered environment or an area with monoculture/near monoculture invasive coverage provided the sprayer tip is kept lower to the ground and droplet size is increased to reduce drift. Spraying during still air can also be problematic due to thermal inversions, where air near the ground is cooler and denser, trapping spray droplets and allowing them to drift horizontally.

Dauber bottles excel at minimizing off target application.

High-Pressure Power Sprayers can help professionals or those with acres of dense invasive species coverage manage large projects efficiently. These sprayers have high potential for off-target application and should only be used by trained and knowledgeable individuals.

Avoid High Temperatures - Spraying during the heat of the day can cause the droplets to evaporate before they reach the target, which increases the risk of drift and reduces effectiveness. Additionally, plant intake of herbicide can be reduced at extreme temperatures approaching or above 100 degrees Fahrenheit. Read your herbicide label for guidance on the recommended temperatures for that specific formulation.

Using the Correct Formulation

Water-Soluble vs. Oil-Based - Formulations Water-soluble formulations are less likely to volatilize (evaporate into a gas), which can reduce drift. Volatile products can move off-target even in calm conditions after they have been applied.

Granular vs. Liquid - In some cases, granular formulations may be preferred, especially in areas prone to drift. Granules are less likely to move in the air compared to liquid sprays.

Aquatic Safe Herbicides - Some herbicide formulations are permitted to be sprayed in flood planes, adjacent to water, or even directly into the water. Read your herbicide label to understand its environmental considerations and locations it can or cannot be used.

Broad Spectrum vs. Selective – Broad Spectrum Herbicides attack a wide range of plants whereas selective herbicides may target a specific family or grouping of plants. An example of a selective herbicide includes Alligare Triclopyr 3 which targets woody plants, vines, and broadleaf weeds.

Buffer Zones and Target Identification

Create Buffer Zones - Establishing a buffer area between the target zone and sensitive areas, such as water bodies, wildlife habitats, or non-target crops, can significantly reduce the risk of unintended exposure. The size of the buffer zone will depend on the terrain, the type of product used, and the application method.

Know Your Surroundings - Before application, survey the area to identify non-target plants, crops, or environments that may be sensitive to chemicals. Protect these areas by adjusting application methods or selecting products with reduced off-target risks.

Buffer Zones can help protect more sensitive areas that require different management strategies.

Maintain and Calibrate Equipment Regularly

Regular Maintenance - Clean and check your equipment regularly to ensure everything is working correctly. Worn nozzles or malfunctioning pressure regulators can lead to uneven application and increased drift. Spray nozzles and hoses should be purged of herbicide after every use. Built up pressure and corrosive herbicides can destroy the O-Rings that are essential for proper sprayer function and safety.

Calibration - Calibrating your sprayer ensures that the proper amount of product is being applied. Over-application can increase the likelihood of off-target movement, while under-application can reduce effectiveness.

Spray Techniques to Reduce Drift and Off Target Application

Spray Close to the Target - The closer you spray to the target plants, the less chance there is for drift. Use a shielded sprayer for added control, especially in windy conditions or near sensitive areas.

Direct Spraying - For weeds or pests located close to desirable plants, direct spray techniques such as spot spraying or wicking can be used. These methods allow for targeted application with minimal effect to surrounding plants.

Adjust Spray Angle - When using a boom sprayer, angle the nozzles forward to ensure that droplets hit the plants directly. This reduces the amount of spray that can be carried away by the wind.

Adjust Spray Nozzles – Most spray nozzles have adjustment settings to change whether your spray is a finer mist, a stream of herbicide, or somewhere in the middle. Usually somewhere between a mist and a stream of herbicide is ideal as it maximizes sprayer coverage while minimizing drift potential.

Spray on the Lowest Pressure Possible – Whether your sprayer is a hand-pump or powered by a gas/electric motor it should be able to adjust the spray pressure for the setting. Lower pressure reduces overspray, especially on individual or dispersed plants whereas higher pressure can make it more effective to pray large monocultures of undesirable plants.

By changing the nozzle type on your herbicide sprayer and fine-tuning its settings you can change the profile of your spray for different applications.

Use Drift Control Additives

Additives - These products can be mixed with your spray solution to increase droplet size, making them less prone to drift. Always follow the manufacturer's guidelines for proper use.

Personal Safety Measures

Protective Gear - Wear appropriate protective gear such as gloves, masks, and long-sleeved clothing to prevent exposure to the chemicals you're applying.

Proper Handling - Follow all safety guidelines when mixing and applying chemicals, and be sure to clean all equipment thoroughly after use to prevent accidental exposure.​

Conclusion: When used properly and responsibly, herbicide application can be one of our greatest tools for invasive plant management and control of unwanted weeds. By taking a site-by-site approach to management strategies we can maximize our efforts while minimizing negative effects of herbicide application. For assistance with choosing herbicides, understanding application method, purchasing the right equipment and more contact your local Soil and Water Conservation District or Extension Office. ​