Battling herbicide resistance

Photo: ©istock.com/Whiteway.
Mississippi State University researchers say herbicide-resistent groundsel was reported as early as 1970. Photo: ©istock.com/Whiteway.

With herbicide resistance a reality in agriculture and golf, lawn care could be next.

Lee Kral, lawn care manager at Mountain High Tree, Lawn & Landscape Co. in Lakewood, Colo., got a reality check about seven years ago. That’s when, through a colleague’s father, he learned about glyphosate-resistant crops in agriculture production.

He’s been keen on weed resistance ever since. And while he’s seen no signs of weed resistance on the job, “I’m extremely concerned about it,” he says.

That’s because glyphosate is a common active ingredient in popular herbicides, such as Roundup. Weeds like annual bluegrass have shown resistance to it among row crops and golf course turf, limiting the number of weed-killing tools available to turf managers.

“We’ll need to find alternatives that are as effective as glyphosate used to be while also reducing the risk to the environment,” Kral says.

Brian Beane, vice president of Nature’s Select Premium Turf Services in Winston-Salem, N.C., shares Kral’s sentiments. After all, he’s watched farmers in eastern North Carolina experience resistance to Roundup. “So it is a concern,” he says.

How prevalent is resistance in lawn care?

The fact is, weed resistance is not yet an issue in the lawn care industry as it is in agriculture and golf. Virtually no one interviewed for this story had yet witnessed herbicide resistance among lawn weeds. Take Mike Stephens, general manager of Always Green of Cape Cod, based in Marstons Mills, Mass.

“I’m not really concerned about it,” he says. “I really haven’t seen it.”

So is Kral’s and Beane’s concern justified?

Absolutely, say turf researchers.

Landscape professionals “should definitely be concerned about weed resistance,” says Jim Brosnan, Ph.D., associate professor of turf and ornamental weed science at University of Tennessee. “Herbicide-resistant weeds are emerging at increasing rates in all facets of agriculture, and turf is by no means immune.”

Based on what researchers have observed in other agricultural sectors, Brosnan says, “This is only bound to increase.”

Weeds become resistant to herbicides due to lack of diversified weed management methods, turf scientists say. Managers find an effective herbicide, then use it year in and year out without rotating in different products.

In the end, weeds build resistance to the herbicide’s mode of action. It’s exactly what’s happened in agricultural production systems, and it’s happening in the golf industry now.

Scott McElroy
Scott McElroy

Scott McElroy, Ph.D., a professor in Auburn University’s department of crop, soil and environmental sciences, asserts that while researchers simply have not seen the resistance in lawn care that they have in row crop agriculture and golf, researchers are less likely to hear from landscape and lawn care professionals than they are turf managers in the golf, sod and sports turf industries. That void could disguise a problem.

“People in the lawn care industry simply do not communicate with (researchers and professors) like me. I simply do not hear about the problems they are having,” McElroy says. “They’re much less likely to reach out and say, ‘I’m having trouble getting control and can you help me?’”

So perhaps there’s more herbicide resistance in lawn care, where “time is money,” than people realize, he says. He also cautions lawn care managers to consider “not all failures in weed control are their fault. It may be resistance that’s actually developed.”

Lawn care operators who believe they’re exempt from resistance problems are mistaken, Brosnan says, especially “given the ‘rounds’ nature of the business.” And as a weed scientist, he’s disturbed he’s not seeing products used in rounds change from year to year.

“These products only encompass a handful of different modes of action,” Brosnan says. “If we lose one or two of these due to resistance, options will become quite limited, and weeds will become much harder to control to a commercially acceptable level.”

Rotate herbicides now

Lawn care operators can avoid this problem by regularly rotating the herbicides they use. Beane’s taken advantage of the variety of selective broadleaf herbicides on the market.

“Due to the fact that we have a rotation policy, we have not seen evidence of weed resistance,” he says.

Neither Beane’s nor Kral’s customers care about potential resistance, if they’re even aware of it at all. All they care about is a healthy lawn, they say. To keep healthy lawns a reality for their customers, neither operator is taking any chances. For broadleaf weed control, Kral has turned to non-2, 4-D products, and he rotates them mid-season.

“I am trying to stay in front of the problem, rather than having to deal with a resistant weed or insect,” he says. “One thing I am convinced of is when we start to see some resistant weeds out there, we need to kill them with a different formulation of pesticides before they can become firmly established.”

Stephens says that while he may “switch it up a bit” to better control a problematic weed, he hasn’t officially rotated products.
“I always tend to be more optimistic, thinking that there’s always going to be something new they’ll come out with that will help,” he says. “If it ever becomes totally resistant, it would be of concern, of course, but it seems there are continually new products coming out. I’m confident in the industry.”

Cultural practices important, too

Jim Brosnan
Jim Brosnan

As vital as chemistry rotation is, Brosnan warns it’s not enough without wise practices such as proper nutrient applications and irrigation.

While more attention finally is being paid to cultural practices in row crop agriculture, where resistance is prolific, “in turf the resistance is still isolated and many are following this same troublesome pattern,” Brosnan says.

Kral is doing what he can to avoid it. Sure, rotating herbicides is crucial. “But keeping lawns healthy and strong so weeds can’t get established in the first place is another good way to not have to use as much herbicides,” he says.

The big danger

So what happens if resistance does become a problem in lawn care?

“Herbicides no longer working would be the biggest fear you’d have,” McElroy says. “That’s why it’s so important for lawn care applicators to think about the long-term ramifications of their actions. If a herbicide application doesn’t work, people don’t take the time to figure it out. They just say, ‘OK, let me go apply another one.’ The answer of going and applying another herbicide is shortsighted.” Instead, lawn care operators need to think long term, he says.

Just imagine if today’s most popular herbicides were no longer viable weed control options for a lawn care operation, Brosnan says.

“These are the real consequences of what can happen if resistance gets out of hand,” he says. “Operators will be stuck with limited herbicide options and forced to either physically remove weeds or communicate to customers that certain weeds will not be able to be removed… That’s going to be a tough sell in my opinion.”

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Beth Geraci

Geraci is a freelance writer based in Cleveland. She has worked as a professional journalist for more than 15 years, including six years as a writer for the Chicago Tribune. A graduate of Allegheny College and Northwestern University’s Medill School of Journalism, Geraci began her career as an editor at a newswire service in Washington, D.C., where she edited and distributed press releases from the White House and congressional leaders. She went on to become the community news reporter at the Jackson Hole Guide newspaper, winning two national feature writing awards. Her other experience includes working as a book editor in Chicago and as a professor of business communications at Cleveland State University.

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