Every cotton farmer understands that applying pesticides on a windy day is a bad idea. But a complete lack of wind can be an issue, too. It’s important to watch wind speeds and apply when winds are in the ideal range.
A temperature inversion is a weather condition that can allow pesticides to move beyond the field of application. It occurs when a layer of warm air covers a layer of cooler air, effectively putting a lid on the surface-level air that prevents it from rising and mixing normally into the upper atmosphere.
Gases trapped near the surface may shift sideways instead. Pesticides that have volatilized (turned to gases) can move into neighboring fields, lawns and gardens with unintended consequences.
“No wind is not a good thing for herbicide applications,” says Haley Nabors, Enlist™ field specialist. With temperature inversions, products can move significant distances. “Furthermore, you don’t know which direction it will move.”
What to look for
Nabors cautions farmers to watch for conditions that create temperature inversions and avoid spraying pesticides in those conditions.
“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.
“In some cases, particularly in West Texas and New Mexico, low humidity means we won’t see any fog,” she says. “We may not have any visual signal of a temperature inversion.”
Monitor with technology
Without visual clues, how can farmers identify a temperature inversion? If you carry a smartphone or tablet, you can check local weather reports to find out if conditions favor the formation of an inversion. Many weather reporting organizations offer downloadable apps to help monitor local conditions, but always check conditions in the field, too. Keep in mind that temperature inversions are most likely when wind speeds are less than 3 mph and/or if the temperature remains within 5 degrees of the nighttime low.
“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.
Check conditions before and during every application. Check nighttime and current temperatures. An inexpensive windsock will show wind direction. An anemometer provides wind speed.
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 safely dissipate any potential inversion layer.”
Enlist Duo® herbicide contains new 2,4-D choline and glyphosate, while Enlist One™ herbicide is a straight-goods 2,4-D choline product that offers greater tank-mix flexibility. Both feature Colex-D® technology, which limits drift and provides near-zero volatility after application. Enlist herbicides should not be sprayed during a temperature inversion.
Remember to check the wind and make sure it’s in the proper range — neither strong nor too light. Do not apply any herbicide during a temperature inversion.
®™ Trademark of The Dow Chemical Company (“Dow”) or E. I. du Pont de Nemours and Company (“DuPont”) or affiliated companies of Dow or DuPont. 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 are the only 2,4-D products authorized for use on Enlist crops. Always read and follow label directions. ©2018 Dow AgroSciences LLC.