Dick Oliver, University of Arkansas weed scientist, stands well over 6 feet tall. In mid-July, plenty of the weed-choked field behind him — healthy horseweed and Palmer amaranth abound — was taller.
“To maximize your weed program, you need to know about your weeds,” Oliver said to a group touring the University of Arkansas research station at Clarkedale, Ark. “So why is this plot total horseweed while (an adjacent) plot is a mix of weeds? What caused that?”
“Chemistry,” says someone in the crowd.
“Not bad! So how in the world did we take a weed like horseweed — that 15 years ago wasn’t a problem weed — and make it a huge problem? Is it because of biology?
“Well, we sprayed Roundup and killed it repeatedly. Then, all of the sudden, it became resistant. At the same time, we went into no-till systems in big acreage. That’s how we made horseweed one of the top three weeds in the South in about a five-year period.”
What makes a weed like horseweed, Palmer amaranth or johnsongrass more competitive than others? Genetic potential, density and a favorable environment, says Oliver. And Arkansas has all three in abundance.
There is good news, though. The LibertyLink technology will be available in soybean varieties next year.
Bayer CropScience promises its new technology will be in high-yielding, excellent varieties from proven companies. Growers increasingly tormented with glyphosate-resistant weeds, or those who want to forestall such from entering their fields, will want to give LibertyLink soybeans serious consideration.
For the layperson, the technology appears to work much the same as Roundup Ready and glyphosate. LibertyLink soybeans can be sprayed with Ignite, a herbicide that works well on a plethora of problem weeds.
But at the recent LibertyLink field day in Clarkedale, speakers repeatedly warned growers not to see the new technology as a simple replacement for Roundup Ready.
“All day today, I hope you hear, ‘This is not glyphosate in a different color jug. This is not the Roundup technology in a different color bag. This is different. We’ll manage it differently and farm it differently,’” said Ken Smith, Arkansas Extension weed specialist.
One of the keys to managing weeds in LibertyLink soybeans is early application of Ignite. Don’t wait too late to apply the herbicide.
“When weeds are sprayed (with Ignite) at 3 inches, it looks good. The problem is weeds don’t all come up at the same time. When the majority of the weeds are 3 inches tall, some are already 8 inches tall. One here, one there. It’s common to think, ‘Well, I can’t afford to spray those until all reach 3 inches tall.’ But that means the ones that are already 8 inches tall will be escapes.”
This is the second year Bob Scott and colleagues have been able to study LibertyLink soybeans.
“We’re excited about getting this technology in Arkansas — we’ve got five glyphosate-resistant weeds, now,” says the Arkansas Extension weed specialist. “This LibertyLink technology is coming along when we need it.”
Scott’s trial at Clarkedale was also put in at five other locations scattered around the state. Those include a red rice location, a rice/soybean rotation that “mostly deals with barnyardgrass control,” and a study at Newport looking at Palmer amaranth control.
“Our research has primarily been focused on using Ignite in a LibertyLink system. We’ve looked at various rates, timings, and the use of residuals. This will be different than when glyphosate was introduced. When glyphosate was introduced, it was Roundup only until fields were clean.”
From the start, says Scott, Bayer promoted many residuals in the company protocols — “Valor followed by Ignite, Prefix followed by Ignite and other weed control programs. … That’s one of the big differences between the introduction of LibertyLink and Roundup Ready beans.”
Again, spray early
Like Smith, Scott emphasized Ignite application timing. Over the years, growers have been able to push glyphosate treatments in Roundup Ready programs later and later. Even so, “at the end of the year we were able to clean the fields up — at least until the arrival of these resistant weeds.
“With Ignite and the LibertyLink technology, we won’t be able to do that. Ignite is not glyphosate. It must go out much earlier in order for you to be happy with it. At our pigweed location, for example, it must go out on 2-inch or 3-inch pigweed. That’s typically seven to 10 days after planting. If we wait a week past that, on 4-, 5- or 6-inch pigweed, there are some control failures. And you must have a sequential in order to clean it up.”
The need for early spraying is also evident at the Lonoke test location where barnyardgrass is the primary target.
“Ignite is a bit weaker on grasses than glyphosate is,” said Scott. “The Ignite application has to go out on smaller, two-leaf to three-leaf barnyardgrass to control it. That’s another major difference.”
As for residuals, “the protocol we’re standing in front of includes Valor at several formulations and combinations including Valor/Sencor. It also has Prefix, all applied pre, and we come back with a post application of Ignite. All those fit well in the LibertyLink system.”
It’s been interesting to have the same testing protocol at the different test locations. “For example, at the pigweed test location, putting Valor in pre — really any of the Valor combinations — worked very well. At Lonoke, the barnyardgrass location, Prefix — which contains Dual — looked the best as a residual.”
When spraying Ignite, there are several considerations.
“One is: I’ve got to get my volume up, my coverage right,” said Smith. “That’s because Ignite is not translocated throughout the plant as well as glyphosate. Translocation that does occur is mostly directed upwards, not much downward.”
Smith and colleagues have seen some differences in spraying nozzles, speeds, and volumes. “I believe our spray techniques will need to be refined some when we begin using Ignite.”
Smith points to work done in Poinsett County on nozzle-top effects on horseweed. “We put out 12, 15 and 20 gallons per acre with (AI and flat fan) tips. This shows, on horseweed, the AI tips don’t provide quite the control seen with flat fans until we get into the 24-ounces per acre range.”
Agricultural engineers who have looked at the LibertyLink system “tell us that rather than talking strictly about water volume, we need to speak about coverage” said Scott. “Whatever configuration a guy can put in to safely apply, have no drift and get the best coverage possible is critical. Ignite is a contact herbicide and doesn’t translocate as well as glyphosate.”
To apply it, Scott uses 10 gallons of water with flat fan nozzles at 3 miles per hour. “Over the next couple of years, it’s going to be a learning curve for all of us. A big concern is not to drift (Ignite) onto conventional soybeans.”
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