With the recent introduction of soybean and cotton traits resistant to synthetic auxin herbicides, farmers have new, much needed options for managing glyphosate-resistant broadleaf weeds. Researchers writing in the journal Weed Technology say use of the auxins isn’t without risk, though. When the herbicides drift off target, they can cause severe injury to sensitive broadleaf plants, such as cotton, wine grapes and soybeans.

The authors conducted a survey of Missouri pesticide applicators to determine what they knew about the new synthetic auxins and their tendency to drift. More than 2,300 commercial and noncommercial applicators responded. Most all were familiar with physical drift and how to minimize it. They were less familiar with volatility and with temperature inversions, which also can influence off-target movement of auxin herbicides.

Vapor pressure, for example, can influence the volatility of auxins, allowing particles to evaporate from their landing surfaces and move back into the air where they can be moved by wind. Less than half of survey respondents understood the link between vapor pressure and volatility.

In addition, few survey respondents were able to identify all the environmental signs of a temperature inversion, which occurs when the air near the earth’s surface is cooler than the air above it. Many approved auxin herbicide labels say applications should not be made during temperature inversions since small herbicide particles might become suspended in the stagnant air mass at the earth’s surface and move to unintended sites.

“It is clear that further education is needed on the synthetic auxin technologies and how to apply them safely,” says Mandy Danielle Bish, Ph.D., a senior research specialist at the University of Missouri.

This article is freely available for one month, “Survey of Missouri Pesticide Applicator Practices, Knowledge, and Perceptions,” is now available in Weed Technology Vol. 31, Issue 2, 2017.

Blog and Cover image
Cover crops like oilseed radish (Raphanus sativus L.) are increasing in popularity in many corn and soybean production systems throughout the U.S. Research conducted across 3 seasons in Missouri showed that oilseed radish is one of the most sensitive cover crop species to common herbicides used in the previous corn or soybean crop. Photo by Kevin Bradley