Farm Progress

Creativity will help stop weed resistance

David Bennett 1, Associate Editor

March 17, 2010

8 Min Read

In 2005, Stephen Powles warned those in U.S. agriculture that an emerging problem with glyphosate-resistant weeds would only worsen — especially in the South.

Powles’ confident assertion was bolstered by what he’d seen happen with weeds in his native Australia where he works as a farmer, professor of plant biology at the University of Western Australia and director of the Western Australia Herbicide Resistance Initiative.

With his prediction now a burgeoning reality for increasing numbers of producers, Powles recently spent three weeks speaking to U.S. audiences about how to tackle a future with glyphosate-resistant weeds. Besides speaking in Florida, Powles — brought to the United States by Syngenta — addressed farmers and consultants in South Carolina, Memphis and New Orleans. (For a look at how Powles saw the situation developing earlier click here).

The day before his journey home, Powles spoke with Southeast Farm Press.

Among his comments:

• Can you bring us up to speed on the agricultural situation in Australia? I understand there’s been a huge drought over the last couple of years.

“It’s important to realize that Australia is a very big country, like the United States. But it’s also a dry country. There are always droughts, but that doesn’t mean the whole country is in drought.

“It’s true there have been nasty droughts in certain parts of the country. Other crop-growing regions have had reasonable moisture.

“Last year, 2009, was a pretty decent year (for moisture). It wasn’t great, but pretty decent across the country.”

• When we first spoke a few years ago, you were talking about the coming problems that the United States would have with glyphosate-resistant weeds. After your current trip and visits to farms, is the problem as acute as you expected it would be?

“When we spoke in 2005 I was warning in talks across various places in the United States that glyphosate resistance would break out. I think it’s accurate that in 2005 very few were listening to that message.

“Now, in 2010 in the South, there is lots of glyphosate-resistant Palmer pigweed. The other day I spoke to many crop consultants from Helena and I said, ‘Glyphosate will be driven to redundancy.’ Nobody wanted to disagree — there were a lot of nodding heads.”

Look back at the 2005 article “where I said there would be widespread glyphosate resistance in the United States, it would be a major problem, it would be an epidemic. And now it’s at the outset of being an epidemic — it’s under way in the South with Palmer pigweed and will explode much more in the South and move farther to the north.”

• A worry is how to maintain conservation-tillage in the face of this increasing glyphosate resistance. Do you see any way farmers can?

“I think they can but not everyone will. Right at the start, I’m a great supporter of no-till agriculture. Just about all the cropping in Australia is no-till. We’ve seen the benefits and know the benefits.

“But as much as I’m an advocate of no-till, I’m an even greater advocate of diversity. So I don’t have a religious attachment to no-till.

“If a judicious tillage is needed to help control a weed problem, it should be conducted. Judicious cultivation is part of ‘diversity.’

“That doesn’t mean we’ll get the mold-board plow out and go across the whole of the U.S. South. That wouldn’t be very smart, and I know retaining con-till while managing resistance is a challenge.

“Larry Steckel, a good man (and weed scientist from the University of Tennessee), showed me some data (showing) one of the first reactions to resistant Palmer pigweed and marestail was a large return to cultivation. Now, though, as farmers have learned to manage at least the marestail, they’ve moved back to con-till.

“So, it’s a challenge. But farmers should be attempting to maintain con-till whilst putting much more diversity in their weed control programs than most currently have.

“I know that’s an easy statement to make and a difficult one to enact in reality. But I can’t state forcefully enough the need for diversity. And diversity is anything that makes economic sense although that varies greatly from one place to another.

“I heard another good, young weed scientist, (University of Georgia weed specialist) Stanley Culpepper, on some excellent data using cover crops as a component to manage Palmer pigweed.

“What I think will happen — and this is based on what’s happened in Australia — is the resistance catastrophe will stimulate creativity. Farmers will soon do some things for weed control they’re not currently doing. Some of these techniques haven’t yet been identified.

“Resistance means change. Farmers will do what it takes not to go bankrupt. Some will, but most won’t let these weeds beat them. But to win the battle, they’ll have to be far more creative, diverse and spend more money and effort on their crop-weed management than the glyphosate/Roundup Ready crop revolution required in the past.”

• The other thing you were warning about years ago is there was nothing in the research pipeline that would salvage the situation. Is that still the case or have your research contacts provided some hope something will be coming out?

“Farmers are unrealistically optimistic that the chemical industry has a whole package of new herbicides that will be produced just when needed. That is false: there are very few new herbicides. Herbicides are very, very difficult to discover.

“Having said that, your farmers will have the option of planting LibertyLink crops. That effectively represents a new herbicide for many. I’m sure U.S. farmers will adopt LibertyLink crops and that’s a good thing.

“In fact, I think it’s such a good thing that they should rotate and diversify those LibertyLink crops with a lot of other things. If they treat LibertyLink crops in the same way as they have Roundup Ready crops, there will be LibertyLink weeds. I hope U.S. farmers will learn from what’s happened with Roundup Ready crops.”

• You have contacts all over the world. Could you comment on glyphosate-resistance picking up speed outside the United States?

“It’s under way and will be, big-time, in Brazil and Argentina. The three big countries for glyphosate resistance will be the United States, Argentina and Brazil.

“That’s because all three countries have massively adopted Roundup Ready crops. The same problems being experienced in the United States are appearing, will continue to appear and will explode in Argentina and Brazil. But leading the pack is the United States.”

• Your current research?

Australian producers “have had a long-term problem with multiple herbicide resistance in ryegrass. We’ve learned that such an environment requires diversity.

“We’ve learned a few tricks to keep such weeds under control. We won’t be forced out of business by the situation. But to survive, we’ve had to introduce some practices into our farming systems.

“One of them is in our seeding rates — and our main crops are wheat, barley and canola — have risen by up to 40 percent. We’ve tried to make our crops more competitive against the weeds because we can’t be so reliant on herbicides. That simple agronomic practice — as well as manipulating our crop-seeding date — has meant we’ve done a pretty good job of suppressing weeds.

“In the United States, over the time the great Roundup Ready technology has been available, seeding rates for soybeans have actually gone down. That’s because it’s been easy to kill weeds with Roundup. I’m not sure if the same is true for U.S. cotton.

“So, U.S. farmers will increase their seeding rate. They won’t want to do that because of the expense. But if you can’t kill the weeds with glyphosate anymore, that’s one thing that will be tried.

“Another thing that’s coming is herbicide rotation. It may be counterintuitive, but I always say to farmers, ‘If you’re getting great weed control with a herbicide, change it!’ Diversify your herbicides.”

In Australia, “we use any herbicide that still works but don’t use them all the time. We rotate them and mix them in a smart way.

“Finally — and this may be considered a bit far out — is Australian farmers have realized we must do something about the weed seed production. We don’t want them to return to the crop field. We have a few no-chemical — as well as chemical ways — of stopping weeds producing seed.

“I think U.S. farmers will find something similar. Dead weeds don’t produce seed and therefore don’t pass on resistance genes.”

• You make use of the ryegrass buggies…

“That’s right — chaff carts, we call them.”

• Are you suggesting that could work in the States?

“I think so. Ask your weed experts what they think. Soybeans are pretty much harvested with a conventional wheat-type combine harvester. Behind these we tow a chaff cart that collects the chaff fraction that contains the great majority of ryegrass seed.

“Now, that only works for weeds that produce seed that doesn’t shatter. Ryegrass seed doesn’t shatter before harvest. So, we harvest the crop and the weeds and then capture the weed seed in the chaff cart. That seed is then disposed of, fed to livestock, whatever.

“There are a number of weeds in the United States where the seed doesn’t shatter. The weeds that do shatter will have to be dealt with differently.

“Another thing we do is simply funnel the chaff and straw out of the back of the combine into narrow windrows which are then burned. That also kills a lot of weed seed.

“In some cases, we have chemicals that are registered for application very late in the growing season. Those are aimed at killing weed seed production.

“Once big-time resistance hits the United States, it’ll unleash all this creativity from farmers and their advisors. We’ll see solutions that aren’t evident at the moment.”

e-mail: [email protected]

About the Author(s)

David Bennett 1

Associate Editor, Delta Farm Press

David Bennett, associate editor for Delta Farm Press, is an Arkansan. He worked with a daily newspaper before joining Farm Press in 1994. Bennett writes about legislative and crop related issues in the Mid-South states.

Subscribe to receive top agriculture news
Be informed daily with these free e-newsletters

You May Also Like