With the amount of money spent on herbicides every year combined with the liability associated with drift, it pays farmers to ensure every droplet stays on the acre. A review of herbicide labels will indicate the need to manage drift and highlight the responsibility of the applicator if an off-target incident occurs. Off-target applications are influenced by several factors. These include, but are not limited to, the products in the tank as well as mechanical and environmental factors.
Drift is the movement of spray droplets to non-target sites during or shortly after application. Farmers can mitigate drift by monitoring the weather and using the right combination of drift reduction technologies, including adjuvants and nozzles. Drift reduction agents (DRA) are adjuvants used in a liquid spray mixture to reduce spray drift. Simply put, they help herbicide sprays stay on target without moving to an adjacent field. DRA requirements are listed on herbicide labels along with the recommended droplet size, referred to as Volume Median Diameter or VMD, which aids in nozzle and pressure selection.
In addition to spray drift, volatility and inversions can also lead to off-target movement. Volatility is the conversion of an applied herbicide to a vapor capable of off-target movement. While all herbicides can drift, only some are subject to volatilization. It varies based on the active ingredient and the formulation. Certain conditions are also more favorable to volatility, including temperatures above 80°F, humidity below 70%, and a lack of rain, dew or irrigation. New regulations instituted in 2021 now require volatility reduction agents (VRA) for over-the-top dicamba tank mixes.
An inversion is an environmental process that keeps the herbicide spray from penetrating the canopy, holding the herbicide droplets in a fog above the canopy. This typically happens in calm conditions early in the morning or late in the evening when there is little cloud cover or wind. When conditions change, the fog or mist containing the herbicide droplets can be carried to non-target sites.
Before any herbicide application this season, always check the label for requirements and guidelines. Visit the herbicide manufacturer’s website for a list of approved DRAs and VRAs if required by the label. For help, work with a Helena representative to help ensure your weed management program is effective and meets all of the legal requirements to mitigate drift.