US may soon lead world in herbicide resistant weeds, warns international expert (10/2/2005)

"Very shortly, I think, the impact of herbicide resistance is going to be huge. I've been saying so for a while, now. So have others. (With recent discoveries of resistant weeds) we've already had a little taste of what's to come, but it's going to be much worse!" Ford Baldwin, veteran Arkansas weed scientist

"The massive adoption of Roundup Ready across vast slices of the United States - along with the persistent usage of glyphosate - is a very strong selection pressure.

"Increasingly, U.S. weeds are surviving glyphosate. And a weed that can survive glyphosate is in herbicide heaven. Its competitors are killed while it can grow and reproduce. This is slowly but surely, and inexorably, occurring." - Stephen Powles, international herbicide expert

U.S. may soon lead the world in herbicide-resistant weeds
By David Bennett
Delta Farm Press, Feb 10, 2005

While newly-arrived Asian soybean rust hogs the media spotlight, a home-grown monster patiently awaits its turn. If weed scientists are correct, the monster won't have long to wait.

"Very shortly, I think, the impact of herbicide resistance is going to be huge," says Ford Baldwin, veteran Arkansas weed scientist and Delta Farm Press <contributor. "I've been saying so for a while, now. So have others. (With recent discoveries of resistant weeds) we've already had a little taste of what's to come, but it's going to be much worse! Sometimes it's hard to break through with bad news. Folks don't want to hear it because they really like newer technologies like Roundup Ready. But it's coming."

As the list of herbicide options shrinks, Stephen Powles points to his native Australia as a lesson to U.S. agriculture. Powles - "the international expert on herbicide resistance," says Baldwin - warns there's too little diversity in U.S. fields, there's too much reliance on glyphosate and the pipeline for new herbicide chemistries is "nearly dry."

Powles, director of the Western Australian Herbicide Resistance Initiative (WAHRI), is currently visiting the United States. Following a late-January meeting with weed scientists in North Carolina, he spoke with Delta Farm Press.

Among his comments:

*Please describe the environment, or environments, farmed in Australia. Is it a diverse landscape akin to the United States?

"Australia is about the same size as the continental United States. The big difference is we've only got 20 million residents, compared to your 290 million. There are an awful lot of similarities culturally between the two countries.

"Agriculture is a very important part of the Australian economy. Farms are very large there. Most serious family farms are 10,000-acre enterprises and are dominated by wheat.

"But just about all other crops are grown. There's a vibrant cotton industry. There's a small, but vibrant, rice industry as well. Since it's such a big country, there are areas suited to different crops. But it isn't nearly as blessed agriculturally as the United States."

*Can you offer a quick sketch of your career and what you're involved with now?

"I've worked and studied in Australia, the United States and Europe. I began to see (herbicide) resistance in weeds showing up in the United States and Europe and thought, 'Well, this must also be occurring in Australia.' I decided to work in the field and found that not only had resistance occurred in Australia but had absolutely exploded. By far, we now have the biggest herbicide resistance problem in the world."

*How did it come about?

"Thinking back to how the United States was settled by Europeans, it was a march westward. They developed agriculture as they went. In Australia, the same happened. When Europeans settled in 1788 onwards, agriculture came with them. But the chief industry they brought was sheep because the animal was very well-suited to the climate. So sheep numbers built up dramatically - at one time, there were 400 million.

"The sheep had to eat something and the native prairies and pastures weren't suited to sheep grazing. So they brought in a great, valued pasture feed: ryegrass. The same grass farmers in America are familiar with was nurtured and planted in great density over 150 million acres. If you like, across half the continent ryegrass pastures were established for huge sheep farms.

"For 100 years sheep were kings, and ryegrass, by association, was, too. But about 1970 the price of sheep and wool began to drop. Eventually, cropping became king and ryegrass pastures were converted. There was always a small wheat industry in the country, but it started to really develop big-time.

"So now, imagine with me, you have a continent and across the southern half ryegrass has been planted at very high densities. Then, you convert that into one big no-till wheat field with very little diversity. Then you spray the hell out of this field with herbicides because now this plant, ryegrass, that youÕve encouraged for decades is your number one weed."

*What products were being used to select ryegrass plants out with?

"What enabled this farming system to work was the development of the burndowns - mostly paraquat and, 10 years later, glyphosate. Then, what really made it work were the selective herbicides like Hoelon that didn't kill the crop but did the weeds.

"In Australia, the sheep industry was the reason for planting this weed, ryegrass. That was fine until there was a change in farming from livestock to cropping. When that change happened, we'd set ourselves up with the world's biggest weed problem and potential for resistance.

"Ryegrass is highly genetically variable, is cross-pollinated and can easily develop resistance. As soon as we began selecting it with good herbicides like Hoelon, it quickly developed resistance. And it didn't just develop a resistance, but multiple resistances to many herbicides. I mean, we have ryegrass that's already resistant to herbicides yet to be discovered."

*By spraying so much, did weeds other than ryegrass become resistant?"

"We do have other problems, but ryegrass dwarfs other weeds. It's so dominant it actually suppresses other weeds."

*Can you describe how you control this? In a typical year does it sprout everywhere on a farm?

"Every farm field in Australia has ryegrass. Farmers there have learned to manage this multi-resistant weed. They're doing fine, but not without considerable cost and planning.

"The first thing Australian farmers have to do is continue making money - and they're working with no subsidies. They can't go out and do impractical things. For instance, they can't go with cultivation because the soils aren't suited for that. Plus, labor is extremely expensive in Australia. There are many constraints.

"So what are they doing? First, they use any herbicides that still work. For example, the burndown herbicides - paraquat and glyphosate - are extremely important. Thus far, there has been very little resistance of ryegrass to the burndowns. They have also found ways to use other herbicides creatively."

*What methods would that include?

"All Australian farmers are using the 'yellow' herbicides. Everyone knows the yellows should be incorporated into the soil. But we can't do that since we're in no-till systems. Yet, we've learned how to use them in no-till situations. By getting a bit of soil 'throw' during seeding operations, a higher rate of the herbicide can be used. By getting just a bit of soil to cover it, it works.

"We've also learned that we must look to non-herbicide solutions. So crop seeding rates have been increased 30 percent to 50 percent. This makes the crop more competitive against ryegrass. We wouldn't do that if herbicides alone worked.

"Some farmers also use devices attached to the harvesters - sort of a trailing chaff cart. These catch the ryegrass seed instead of returning it to the field. That seed is then burned or fed to livestock.

"Ryegrass seed is small and has the advantage of not shattering. When a wheat crop is harvested, the ryegrass seed is still attached to the plant. You can get a lot of the seed going into the harvester. If you can separate that out, it's a great way to keep that seed from returning to a crop field. This practice has become very important for us.

"All of this can be summed up in one word: diversity. What was wrong - and still is wrong - with Australian cropping is a lack of diversity. That's the same thing wrong with U.S. agriculture. Weeds like ryegrass love a situation with little diversity."

*You travel frequently and are very familiar with what's happening around the world agriculturally. If trends continue, what do you see for the United States and weed resistance?

"Your readership knows that the United States is the most technologically advanced nation in the world. They don't need some Australian telling them anything - we're used to receiving messages from you, not giving them.

"But there is something Australia is number one in the world at: herbicide resistance. We know about this problem and have the dubious distinction of being tops.

"However, the United States is about to take the top spot away from us. My prediction is you will be crowned king of herbicide resistance within the next few years.

+What have your American weed scientist friends said when you tell them that?

"I think there's a number of university weed scientists that are incredibly concerned with this. You should seek their words rather than have me put words in their mouths. In our discussions, though, they are very concerned with the massive over-reliance on glyphosate in Roundup Ready crops.

"The advent of Roundup Ready is a fantastic technological development. It was a leap forward and was rightfully embraced by U.S. growers. The system is very attractive.

"But relying too much on any one biological system will have repercussions. The massive adoption of Roundup Ready across vast slices of the United States - along with the persistent usage of glyphosate - is a very strong selection pressure.

"Increasingly, U.S. weeds are surviving glyphosate. And a weed that can survive glyphosate is in herbicide heaven. Its competitors are killed while it can grow and reproduce. This is slowly but surely, and inexorably, occurring.

*You've mentioned red flags you've seen in the United States. With those in mind, what would you do immediately and long-term to address the problem?

"In the end, this gets down to a farm-by-farm and field-by-field decision. You can't make sweeping generalizations about the United States - it comes down to specifics. But the specifics always come back to one common theme. That theme is, again, 'diversity.' There has to be diversity in cropping systems if they're to be sustainable.

"A cropping system that is a Roundup Ready crop followed by another followed by another and on and on isn't sufficiently diverse. I tell Australian farmers all the time, 'If you strike on a good herbicide, don't stick to it. If you're getting fantastic weed control with glyphosate, change it anyway. Same is true for paraquat. Rotate the herbicides and use any non-herbicide tools that make economic sense. Have as much diversity as you can stand.'

"These are well-established principles that are widely accepted as truth around the world. Of course, economic realities drive decisions and the many benefits that Roundup Ready crops have given U.S. agriculture in particular make it easy to stick with. Diplomatically, I'd tell the U.S. grower that there's a serious over-reliance on glyphosate, and that puts the world's greatest herbicide at risk.

"I believe farmers here instinctively know that. But family livelihoods are involved.

"And I say to them, 'We all live in a pragmatic world. We're used to economic realities. But there is also a biological reality here too."

"The truth is farmers are applied biologists. The biological reality is that glyphosate is a very precious resource. I'd argue that glyphosate is up there with penicillin as a once-in-a-hundred-years discovery.

"I know the vast majority of farmers want to leave their farms to their children in better shape than they found them. Those same farmers want glyphosate to work for the next generation.

"There aren't a bunch of new chemicals in the pipeline that will be available to replace glyphosate. There are none being developed anywhere near as good as glyphosate. The pipeline is, in fact, pretty dry.

"The international herbicide discovery industry - now a number of companies counted on one hand - is busy looking for new chemistries. And it will find them, although with increasing rarity. It certainly isn't finding new herbicides at the rate it used to.

"Something that I face everywhere is a belief by farmers that the next great herbicide is almost ready for release. There seems to be a desire to think that new herbicides will show up whenever needed.

"I don't blame farmers for holding that view. In large measure, that's been their experience. But the pipeline for unique, new herbicides is nearly dry.

*Is Europe in the same herbicide resistance boat? India? South America?

"In general, herbicide resistance has so far occurred in big, industrialized agricultural landscape. That means Australia, the United States, Brazil, Canada and Argentina. That's where there are large fields, minimum till and lack of diversity.

"There is some weed resistance in Europe, but not at the same level. Europeans have a much more diversified agriculture. They typically work smaller fields and have a rotation of a whole range of crops, and cultivation is routine.

"That said, we're also beginning to see resistance develop in less-industrialized countries like India, China, Thailand and other rice-producing nations."

Editor's note: for more information on Powles' work, visit

[email protected]


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