Weed concerns go global

Feb 22, 2013
by DTN

Nearly 300 weed scientists from 33 countries are Down Under last week, digging into the science of herbicide resistance. Stephen Powles, Australian Herbicide Resistance Initiative (AHRI) director, told DTN in an interview that the evolution of herbicide resistance in weeds poses a real threat to global food production and security.

“Especially in the major global grain crops such as rice, wheat, maize and soybean, herbicide-resistant weeds are a real threat to productivity,” Powles said. “We must win the battle against herbicide resistance, just as medical science must win the battle against antibiotic resistance. To do so, we need good science coupled with good agronomy and good engineering.”

Australia has been at the center of the herbicide-resistant weed battle. Annual ryegrass, Lolium rigidum, is the most serious and costly weed of cropping systems in the southern grains region of this country.

“When Europeans moved to Australia, they started a sheep industry, and they planted ryegrass across the nation when the sheep was king. For 100 years, our agriculture was 300 million sheep,” Powles said.

About 50 years ago, much of that land began to be converted to cropping. “We had huge populations of ryegrass on every field that we belted hard with herbicides in notillage agriculture with no diversity. It quickly evolved resistance all over the place. So we created our own problem,” he explained.

In Australia, herbicide resistance in annual ryegrass has been confirmed in 10 different herbicide groups. Herbicides that have diminished utility include common names such as glyphosate, paraquat, atrazine, diuron and trifluralin, among others.

U.S. growers have recently found benefits in using a different species of annual ryegrass, Lolium multiflorum, for cover crops. Powles said he understands the value of that system, but sends a warning. “Everyone should be aware that ryegrass is the world’s greatest resistance champion. It can easily evolve resistance, so you cannot continue to use any single herbicide,” he noted.

Australia is dominated by wheat and Powles explained that Australian farmers have nearly all adopted no-till. “So there’s no diversity and they’ve used low [herbicide] rates. It’s a recipe for resistance,” he said.

Wild radish is another weed species causing major headaches. “It is our version of Palmer amaranth and waterhemp in the U.S.,” Powles said. “It is a really nasty weed and it is evolving resistance to a lot of the herbicides, not as fast as ryegrass did, but then we had huge numbers of ryegrass.”

Powles has been a valued adviser to U.S. weed scientists and farmers as they seek to battle back against herbicide resistance. This week’s conference, the first of its kind in 30 years and the first ever in the Southern Hemisphere, reflects a global reinvigoration of research and international collaboration on herbicide resistance. Chemical company scientists are also in attendance. Powles hopes the venue will draw minds together to come up with cooperation and solutions for the common good.

“In the U.S., the weed control is nearly 100 percent achieved with herbicides. The entire system has greatly overused Roundup Ready crops. It is a great technology that has been overused and is being driven to redundancy over vast areas.

“Reaching for the next jug every year, and using the same jug, that lesson is being learned with glyphosate. “The farmers and all those that advise them realize that any herbicide used across large areas with no diversity will result in resistance,” Powles noted.

“If every U.S. (farmer) switches from Roundup Ready crops to LibertyLink crops, there will be glufosinate resistance. It’s that simple.” — Pamela Smith, DTN