Don’t use herbicides in heat

Published 12:00 am Sunday, August 2, 2015

Pesky weeds might be thriving this time of year, but the middle of a scorching Mississippi summer isn’t the best time to do something about it.

Most herbicides available to homeowners are not meant for use in extreme summer temperatures because they vaporize, and the vapor cloud will travel off target, said Mississippi State University professor John Byrd, who is a research expert in invasive weeds.

“A lot of people are thinking about controlling weeds this time of year because they’re visible. I want to remind you to be cautious if you’re using products to control weeds,” Byrd said during a recent Quick Bites videoconference at the Warren County Extension Office.

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The active chemical in the vast majority of commercially available herbicides shouldn’t be used in the Mississippi heat.

“When we’re having temperatures like we’re having now, the likelihood of injury to, whether its tomatoes or squash in the garden or whether it’s some ornamental in a landscape bed, is significantly increased,” Byrd said. “We might be better off in some cases to wait a little bit later and get through this heat surge before we start using some of those herbicides.”

Herbicide vapors also don’t respect property lines, so damage can be spread around the neighborhood.

“Let’s just say it can cause hard feelings between you and your neighbor,” Byrd said.

Applying herbicides late at night or early in the morning can help reduce vaporization, but when temperatures approach the century mark the next day, expect the poison to dissipate.

“Even if you spray those at night, there’s still potential for volatility, vaporization and nontarget movement a day or two after those have been applied,” he said.

With much of the state facing abnormally dry conditions, even if the weather cools off soon, herbicides aren’t likely to do much good.

“Remember that herbicides don’t work very well if the environmental conditions are not favorable for plant growth,” Byrd said. “Even those products like Roundup that we think of as no-fail herbicides don’t work very well under those conditions.”