“Perfect” weather can spell D-R-I-F-T
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Ahhhh. There’s nothing quite as peaceful and perfect as stepping out the door on a foggy, still, crisp summer morning or watching the sun go down through the mist as a cool summer evening sets in after a hot day.
Though picturesque and enjoyable, these weather conditions can cause havoc with herbicide applications. They are the primary conditions of an air temperature inversion, a weather phenomenon that can cause herbicide spray particles to travel long distances from the field where applied — drifting and damaging sensitive crops and other plants.
What is a temperature inversion?
On a typical summer day, the air temperature is warmest at the ground surface and slowly becomes cooler at higher elevations. As the name implies, the situation is reversed during a temperature inversion. The air closer to Earth’s surface is cooler, denser and heavier than the air higher up. The warm layer acts like a lid, keeping the cooler air from rising into the atmosphere and dissipating.
When an inversion happens, spray particles within the layer of cool air can’t rise. They become trapped under this lid or ceiling of warm air and can drift sideways.
“A temperature inversion creates a risky situation for applicators because spray particles may move long distances in an unpredictable direction to sensitive crops and plants in neighboring fields, lawns and gardens and to wildlife habitats,” says Jason Gibson, market development specialist, Corteva Agriscience.
When to watch for a temperature inversion
Temperature inversions often happen when:
- Wind speed is 3 mph or less. As wind speed increases, the potential for inversions decreases.
- Temperatures in the late evening or early morning are within 5 degrees of the nighttime low.
- Fog is visible at dawn or dusk.
- The sky is clear. More cloud cover slows surface cooling and inversion formation is weaker than on clear nights.
Always check before applying herbicides
“Just because you don’t see ground fog does not necessarily mean that an inversion is not happening,” Gibson says. “It’s always a good idea to check for a temperature inversion if any of the questionable conditions exist.” There are two simple, quick steps:
- Release a smoke bomb or wind chalk into the air.
- Watch how the smoke or chalk moves.
“The smoke or chalk should move naturally with the breeze and mix into the air as it rises,” Gibson explains. “If you see the material gather at a particular height and begin to move sideways, that’s a sign that you’re dealing with temperature inversion. You definitely don’t want to apply herbicides. Wait and check again later for better conditions.”
For more information about temperature inversions and making successful applications, check out the Enlist® weed control system temperature inversion fact sheet or the 2025 Product Use Guide.
Following burndown, Enlist Duo® and Enlist One® herbicides with Colex-D® technology are the only herbicides containing 2,4-D that are authorized for preemergence and postemergence use with Enlist® crops. Consult Enlist® herbicide labels for weed species controlled. Enlist Duo and Enlist One herbicides are not registered for use or sale in all states and counties; are not registered in AK, CA, CT, HI, ID, MA, ME, MT, NH, NV, OR, RI, UT, VT, WA and WY; and have additional subcounty restrictions in AL, GA, TN and TX, while existing county restrictions still remain in FL. All users must check “Bulletins Live! Two” no earlier than six months before using Enlist One or Enlist Duo. To obtain “Bulletins,” consult epa.gov/espp/, call 1-844-447-3813, or email ESPP@epa.gov. You must use the “Bulletin” valid for the month and state and county in which Enlist One or Enlist Duo are being applied. Contact your state pesticide regulatory agency if you have questions about the registration status of Enlist® herbicides in your area. ALWAYS READ AND FOLLOW PESTICIDE LABEL DIRECTIONS. IT IS A VIOLATION OF FEDERAL AND STATE LAW TO USE ANY PESTICIDE PRODUCT OTHER THAN IN ACCORDANCE WITH ITS LABELING. ONLY USE FORMULATIONS THAT ARE SPECIFICALLY LABELED FOR SUCH USE IN THE STATE OF APPLICATION. USE OF PESTICIDE PRODUCTS, INCLUDING, WITHOUT LIMITATION, 2,4-D-CONTAINING PRODUCTS NOT AUTHORIZED FOR USE WITH ENLIST CROPS, MAY RESULT IN OFF-TARGET DAMAGE TO SENSITIVE CROPS/AREAS AND/OR SUSCEPTIBLE PLANTS, IN ADDITION TO CIVIL AND/OR CRIMINAL PENALTIES. Additional product-specific stewardship requirements for Enlist crops, including the Enlist Product Use Guide, can be found at www.traitstewardship.com.