Farm Progress

Herbicide-resistant weeds continue march across U.S. farmland.New herbicide-tolerant crops expect to be released in near future.Weed scientist says viability of new technologies must be protected.

David Bennett, Associate Editor

August 23, 2013

8 Min Read

For the last handful of years, weed scientists at the University of Illinois have been studying some new weed-control technologies that are expected to be released soon. Among them: crops engineered to tolerate dicamba and 2,4-D.

“We’ve been looking at how they respond to the herbicides they’ve been engineered to resist,” says weed scientist Aaron Hager. “Also, we’ve looked at what opportunities these new technologies can offer with respect to controlling some of the weed species we’re having difficulty dealing with, right now.”

One may believe there isn’t much that Illinois and Mid-South agriculture have in common. However, Hager says “there are a lot of similarities between the situations in Illinois and Arkansas. There are some big differences, as well.”

While the most problematic resistant weed species in Arkansas is glyphosate-resistant Palmer amaranth, a pigweed, the biggest problem in Illinois is resistant waterhemp.  Even so, “we’re finding more and more Palmer (in Illinois). In fact, this year we’re finding new populations of Palmer scattered around the state.

“We assume these Palmer populations have moved into the state via seed transport from areas where the species is already well-established. What you have with Palmer is quite a bit of resistance, especially to glyphosate. Also, there is resistance to many of the ALS-inhibiting herbicides.”

As for resistant waterhemp, “we suggest to farmers and custom applicators that the biggest concern is not just glyphosate resistance. What we see as the most challenging scenario currently and in the future with our waterhemp is ‘multiple resistance’ – resistance to more than one herbicide class. In Illinois, it’s very, very common that waterhemp isn’t just resistant to glyphosate but also resistant to one, two, or three other herbicide classes.”

Depending on what crop and variety an Illinois farmer grows, “there may not be a chemical solution for waterhemp control.”

Hager, who will be the keynote speaker at the Arkansas Seed Growers Annual Meeting next January 29, spoke with Farm Press in early August. Among his other comments:

On the coming 2,4-D, dicamba and HPPD technologies…

“One of the things we always try to remind people of is that while these traits – whether resistance to 2,4-D or dicamba – are novel, the herbicides themselves aren’t new. 2,4-D has been around for 70 years. Dicamba has been around for 40 or 50 years.

“The ability to use these herbicides in-crop in soybean is new. But that isn’t to say that we haven’t used these herbicides before on existing weed populations.

“Why does that matter? Well, waterhemp is indigenous to Illinois. However, we never really recognized it as a weed problem to any great extent until the last 15 or 20 years. It’s now become the dominant broadleaf species on most of the farmed acres in the state.

On the spread of resistant weeds…

“A point of reference: I did my first plot work with waterhemp in 1996. I had to drive 2.5 hours to the southwestern part of Illinois to do that work. That’s because around the university there was no waterhemp to work with. That is no longer the problem. You can go to virtually any county in Illinois and find waterhemp.

“Taking that into account – along with the fact that we now have five types of resistance that has evolved in the species – we’re going to be introducing traits (in the coming technologies) that allow us to use growth regulator and HPPD-inhibiting herbicides in soybean. The underlying message is: be careful with them.

“The biology of pigweed species will force us to use the new technologies, force us to grow more Liberty Link crops in the Midwest. But there’s no reason to assume that if we overuse these new technologies like we have others that we won’t compromise the effectiveness of these new technologies. Pigweeds have evolved resistance to almost everything we’ve thrown at them over the years.

“We must steward these new technologies very carefully. Otherwise, we’ll just add another class of resistance to the weeds.”

On timing of commercial release of new technologies…

“The original plan was to have these new technologies in the marketplace by 2014. That changed when USDA-APHIS announced they’d require both Monsanto and Dow to provide an Environmental Impact Statement.

“How long will it be? Hard to say, but my expectation is it will set the registration back 18 months to two years. At the earliest, it may be in 2015 – very likely, 2016.”

I’d like to see a map showing how much farther these problems will have spread by then.

“That would be a scary map! I hate to sound like the ultimate pessimist. I’d rather consider myself a realist. But I tell groups we speak with that the situation is going to get much worse before it gets better.

“The reason we have these very significant challenges now is that we’ve tried to simplify weed management for too long. In reality, farming is a biological system. We’ve tried to simplify that biological system for far too long. And the rule of nature does not like simplicity, nature is all about complexity.

“What’s happened is that these plants, what we call ‘weeds’, are simply responding to what we’ve been doing for the last couple of decades.”

No quick fixes

On those expecting a quick solution…

“I continue to run into folks that say ‘well, if I can just hang on for a couple of years, something new will come around. There will be a new active ingredient in the marketplace that will fix all the problems.’

“That’s not going to happen. There are no new active ingredients. There are some under development but what’s needed as a chemical solution is not another herbicide with a target site identical to other herbicides. We need a novel target site and we haven’t seen anything under development for many years.

“Hopefully that fact provides further weight to what we’re trying to do proactively before these new trait technologies are released. These may be the last things we see for a long time. So, we’d best steward them from the outset or their effective lifespan will be greatly compromised.

“Cold, hard steel is the only option in many cases. If you don’t have any more bullets in your gun, you’ve got to pick up another tool. If your only option is to hire crews to chop it out, economics tend to go out the window.

“Palmer is best described as ‘Satan.’ That gives you an idea about how bad it is.”

On other technologies…

“In the future, drones and the like could help with this in specific circumstances. If you had an instrument that could fly over a field and essentially scout for you, that would be great. ‘There’s some Palmer, I’d best go pull it out before it makes seed.’ That would be a wonderful application for some of these site-specific technologies.

“However, if you’re at a point like some farms in Arkansas with such high densities of Palmer, forget it. If you don’t figure out how to remove that Palmer or use enough residual herbicide, I don’t know how a drone might help.”

On drift potential with the new technologies…

“A lot is being said, a lot of research is being done behind the scenes on drift. It is a very significant concern with manufacturers, regulators, end-users and those downwind from the applications.

“I haven’t seen so much effort to minimize drift occurring before. However, drift will occur at times.

“These are products that at very low doses can cause noticeable effects on non-target vegetation. That doesn’t mean the effects are always lethal but that is cold comfort. The value of the crop may be affected even though the plants don’t die.

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 “There are also potential issues with the non-agriculture communities. What happens if there’s drift across a city’s rose garden? Unfortunately, these sorts of things are likely to happen.

“Everyone knows that cotton is very sensitive to 2,4-D. Now, we’ll be introducing more of that into areas where cotton is being grown? How to handle that?”

Anything else?

“We’re optimistic that we can use these new traits. We need the ability to use some of these herbicides, especially in our soybean crops, on these challenging weed species.

“The best thing we can do well ahead of when these traits are commercially available is to come up with a plan on how best manage them. Resistance evolves very quickly. How do we best manage them so we don’t lose the technologies’ effectiveness?

“Also, how best to make sure that what is in the tank matches up with the seed trait planted in the field. If you put 2,4-D on dicamba soybean, you won’t be very happy with the results – and vice-versa. Having worked with some of these varieties, they look darn similar. I can’t look at two plots side-by-side and tell you which variety is which.

“There are a lot of things to prepare for.”

Note: the ninety-seventh Arkansas Seed Growers Annual Meeting will be held January 29, 2014, at the University of Arkansas Rice Branch Station in Stuttgart.

About the Author(s)

David Bennett

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.

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