Know the warning signs and avoid untimely herbicide applications
A thin layer of fog sits atop a young crop in the early morning hours. It has a peaceful appearance, but these conditions may provoke horizontal movement of surface-level air, causing any trapped particles — such as pesticides — to move into neighboring fields.
What you see may be a temperature inversion. A layer of warm air covers a layer of cooler air and acts like a lid, preventing the cooler air from rising and mixing with the upper atmosphere.
According to the National Oceanic and Atmospheric Administration (NOAA), temperature inversions commonly form when the air near the ground cools at night. Calm winds, clear skies and long nights increases the likelihood of a temperature inversion occurring.
Gases trapped near the surface can’t mix with the warmer air above and dissipate naturally, so they hover near the ground and often drift sideways. Pesticides hanging in this layer of air can move into neighboring fields, lawns and gardens with unintended consequences.
“We want a light wind — 3 to 10 miles per hour — when making a herbicide application,” says Haley Nabors, Enlist™ field specialist. Within a temperature inversion, applied products can move great distances. “Furthermore, the direction the trapped air will move is unpredictable.”
Watch for signs of a temperature inversion
Nabors urges farmers applying herbicides and other crop protection products to watch for common conditions that create temperature inversions. If these conditions occur, avoid applying any herbicides until the environment is favorable for a successful, on-target application.
“We tend to associate temperature inversions with early mornings or late afternoons, dawn or dusk,” Nabors says. “The traditional expectation is that we’ll see a fog hovering over the field during a temperature inversion.”
However, Nabors says in West Texas, New Mexico and other areas with low humidity, the telltale layer of fog may not develop, and therefore, there’s no visual signal of a temperature inversion.
So how does a farmer know if there’s a problem? Temperature inversions are most likely when wind speeds are less than 3 mph and/or if the temperature is within 5 degrees of the nighttime low. That’s why spraying in wind conditions of 0-3 mph is never recommended.
Technology helps farmers identify best application conditions
Farmers should plan to check local weather conditions before making any herbicide application.
“If you identify a temperature inversion, do not make an application,” Nabors says. “The spray particles may never hit the intended surface, which makes the application less effective for your crop. If it doesn’t reach the weeds, you’re wasting your herbicide dollars.”
In addition, farmers run the risk of damaging susceptible plants in nearby fields, lawns and gardens.
Nabors urges farmers to check conditions before every application and even during applications. Weather apps for smartphones and tablets can be useful tools to monitor changing weather throughout a herbicide application. Always monitor conditions while you are in the field. In addition to weather apps or websites, an inexpensive windsock shows wind direction. An anemometer provides wind speed. A quick check of the temperature also is a good idea.
If farmers prefer a visual sign, releasing smoke or powder can indicate particle movement. The smoke or powder should drift gently with the wind. If it gathers in a stationary, suspended cloud, that indicates a temperature inversion, which may cause an application to move far and wide.
“With Enlist herbicides, we recommend a minimum wind speed of 3 mph,” Nabors says. “This allows some stirring in the atmosphere to dissipate any potential inversion layer.”
Many farmers throughout the South who incorporated the Enlist weed control system into their acres have seen great success with the technology when applied according to label requirements. Farmers who grew PhytoGen® cottonseed with the Enlist trait have been pleased with how Enlist herbicides stay where applied. They also attest to the weed control Enlist™ herbicides provide.
Enlist Duo® herbicide contains new 2,4-D choline and glyphosate, while Enlist One™ herbicide is a straight-goods 2,4-D choline that offers greater tank-mix flexibility. Both feature Colex-D® technology, which limits drift and provides near-zero volatility. Like other herbicides, neither Enlist herbicide should be sprayed during a temperature inversion.
Remember, a complete lack of wind is a warning. Do not apply herbicides. Wait until later in the day and check again for a more favorable application environment.
®™ Trademark of The Dow Chemical Company (“Dow”) or E. I. du Pont de Nemours and Company (“DuPont”) or affiliated companies of Dow or DuPont. ®PhytoGen is a trademark of PhytoGen Seed Company, LLC. PhytoGen Seed Company is a joint venture between Mycogen Corporation, an affiliate of Dow AgroSciences LLC, and the J.G. Boswell Company. The Enlist weed control system is owned and developed by Dow AgroSciences LLC. Enlist Duo and Enlist One herbicides are not registered for sale or use in all states or counties. Contact your state pesticide regulatory agency to determine if a product is registered for sale or use in your area. Enlist Duo and Enlist One herbicides are the only 2,4-D products authorized for use in Enlist crops. Always read and follow label directions. ©2018 Dow AgroSciences LLC.