Brent Neuberger is a weed scientist and senior technical sales manager with FMC.

Unless you’re an agronomist, crop protection products can be a tough beat to cover because of all the science behind the brands. FMC has set out to make the job a little easier through a series of short “explainers” on the basic concepts of pest control. For those of you who have covered this industry for years, think of these as refreshers to brush up on your skills.

This month’s topic is “How herbicides control weeds.”

Herbicides control weeds by binding to a specific protein vital for life and inhibiting that protein’s function, ultimately causing the weed to die. This protein is referred to as the herbicide’s “site of action.”

“There are basically 16 sites of action in use for corn and soybean weed control,” says Brent Neuberger, weed scientist and senior technical sales manager with FMC. “The last new site of action discovered was the hydroxyphenylpyruvate dioxygenase, or HPPD inhibitors, in the early 1980s. There are no new sites of action expected in the near future, so we must preserve the tools we have.”

Preserving these tools means using herbicides with different sites of action to help fight herbicide resistance, which develops when the same herbicide with the same site of action is overused. Those sites of action are organized into group numbers, which are printed on a herbicide label. You can find a poster outlining the different sites of action and their group numbers on the website “Take action on weeds.”

“Ideally, a weed management system would contain multiple effective sites of action,” Neuberger says. “Pre-emergent residual herbicides provide the first step to include those additional sites of action, especially when paired with an effective post-emergent herbicide.”

While not expected to provide 100 percent control, pre-emergent herbicides will reduce the number of weeds subjected to the post-emergence herbicides so there is less chance a weed will develop a resistance to them.

“Another way to look at it is that a weed that never emerges will never have a chance to develop resistance to post-emergence herbicides, which are the herbicides that are showing the biggest problems,” he says.

Neuberger recommends including at least two effective sites of action. “For example, in soybeans, Authority^® Elite herbicide is a pre-emergent herbicide containing sulfentrazone, a Group 14, and s-metolachlor, a group 15, providing two sites of action,” he says.

You can read more about how herbicides work in Neuberger’s bulletin, “ABCs of Weed Control.” To request and interview, contact Jodie Wehrspann at [email protected] or Joan Olson at [email protected].

Always read and follow label directions. Authority brand herbicides are not registered for sale or use in California. FMC and Authority are trademarks of FMC Corporation or an affiliate. ©2017 FMC Corporation. All rights reserved. 17-FMC-0607 09/17