Temperature inversions can fuel off-target dicamba movement.
During the daytime, warm air rises when sunlight hits the ground. Meanwhile, cool air comes down, hitting the warm air. When this happens, wind results, which keys air circulation. At night, air patterns flip-flop, with cool air at the bottom and warm air on the top. This creates a stable environment that traps any pesticide particles in a suspended air mass.
When this air mass encounters a horizontal wind, those particles move someplace. At its worst, the trapped pesticide can land in the middle of a multithousanddollar-per-acre field of fruits or vegetables.
Inversions are common, occurring anywhere sun hits the surface of the soil, says Mandy Bish, University of Missouri (MU) senior research specialist. MU researchers have found inversions setting up at 5 or 6 p.m., a time when many applicators are still spraying.
Bish says factors associated with inversions include:
• Clear night skies
• No wind
• Morning dew or frost
• Low-lying fog, which is an indicator of an inversion.
“If you spray the night before you see the fog, it is not the best indicator,” Bish says.
Though not foolproof, smoke bombs are one way to detect temperature inversions. Smoke bombs set off at 4 p.m. by MU scientists showed fairly rapid dispersal. Ones set off at 7:30 p.m. lingered approximately 50 seconds, which indicates inversion presence, she says.