What is in this article?:
- Weed resistance and new technologies
- No quick fixes
- 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.
The most problematic resistant weed species in Arkansas is glyphosate-resistant Palmer amaranth, a pigweed.
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.”