By: John Dietz
With Monsanto’s new Xtend trait in soybeans coming to the market, are there things that growers need to know about applying dicamba?
Once upon a time, perfect weed control became possible – Monsanto put a trait for glyphosate-resistance into canola, then corn, then soybeans and cotton.
In the bigger scheme of things, glyphosate has been “defeated” by pigweed, horseweed, kochia, and other weeds in the U.S.
Now Monsanto has introduced a new herbicide resistance trait on top of the “old” one for glyphosate resistance.
The new crop system, starting with soybeans, was released on February 3, 2016 because the most important soybean buyer in the world, China, said yes.
The new soybean will be resistant to applications of both glyphosate and dicamba herbicides.
In the U.S., it may sustain the ability to produce soybeans in places heavily challenged by weeds with glyphosate resistance.
On the Canadian Prairies, it may generate a weed-free window for soybeans in June and early July and enable a higher yield potential.
New and approved
The new two-trait technology Monsanto has developed is called Roundup Ready 2 Xtend soybeans. It is the first biotech-stacked soybean trait with both dicamba and glyphosate herbicide tolerance.
Xtend is built on the high yielding Genuity Roundup Ready 2 Yield (RR2Y) soybean technology. With the Xtend technology, over-the-top dicamba for tough to control broadleaf weeds is now available for use in soybeans.
This February, China agreed to accept the import of Xtend soybeans and the trait can now be fully released to the market.
The organic chemical 3,6-dichloro-o-anisic acid was registered in 1967 in the U.S. under the common name, dicamba. Trade names were approved in 1983 for Banvel, Banex, and Brush Buster, the first herbicides with dicamba.
Dicamba is a Group 4 herbicide. Group 4 products come from five chemical families and today include 17 active ingredients. Some older Group 4 actives from other families include 2,4-D, MCPA, clopyralid, and fluroxypyr.
In 1995, BASF Canada registered an updated version, Banvel II Herbicide. It is registered to control broadleaf weeds in cereals, field corn, Roundup Ready 2 Xtend soybeans, reduced tillage, pastures and rangeland grasses, crop-free land, red fescue, canary seed, seedling grasses grown for seed, in forage and in low bush blueberries.
“Dicamba is extremely strong on broadleaf plants. It has a wide application window and a powerful residual activity,” says Allan Froese, Monsanto Canada technology development representative, Carman, MB.
He adds, “Original Banvel had a dimethyl amine (DMA) salt. Under the right conditions, like really hot weather and low humidity, DMA dicamba could rise as a vapor and drift miles away onto other crops.”
The BASF product, Banvel II, has the same effectiveness but less volatility. The DMA salt has been replaced with diglycolamine salt (DGA) in the Banvel II formulation.
A Monsanto premix of dicamba and glyphosate herbicides will be branded upon registration as Roundup Xtend with VaporGrip technology, Froese says. It will include an advanced dicamba product, to be branded on registration as XtendiMax herbicide with VaporGrip technology.
Upon regulatory approval, XtendiMax will be labeled for use before, at, and after planting in the Roundup Ready Xtend Crop System.
This low-volatility formulation is expected to provide an additional choice for broad-spectrum control of weeds.
VaporGrip technology is proprietary, designed to significantly reduce dicamba volatility compared to commercially available dicamba products.
Froese says, “VaporGrip doesn’t allow the formation of acid in the spray tank, so it greatly reduces the volatility.”
XtendiMax has a very wide application window, from before the crop emerges up until soybeans are beginning to flower.
The residual effectiveness for XtendiMax will depend on the application rate. Two rates are being registered with Xtend soybeans.
The low rate, 300 g/ha (250 ml/acre), has very little residual control. The heavy rate, 600 g/ha (500 ml/acre), will give 14 days of residual weed control, according to research from the United States.
There are no restrictions for the following crop, with either rate, as long as XtendiMax is applied before September 1.
Xtend soybeans for Western Canada are being developed by Monsanto in Glyndon, Minnesota and Guelph, Ontario. The two-trait beans have been in site trials for at least five years. Test sites in Western Canada have been operating for two years.
The plan is that all Monsanto soybeans will have both traits. Many new lines are in development and older lines will be phased out as advanced varieties come through the breeding process.
“We are seeing better weed control by adding the dicamba at the high rate,” Froese says.
The traditional treatment for RR2Y soybeans is an early burnoff at planting and a second treatment when the crop is up.
But, according to University of Guelph research, a better plan is to have a weed-free period from emergence until the second to third trifoliate stage.
“By adding residual control with the high rate and keeping the field clean, you maximize your yield potential. There aren’t any weeds to compete with your crop,” Froese says. “Timing of the in-crop treatment becomes more flexible. We’d see using XtendiMax in-crop if you have a glyphosate resistant weed or if it’s been too wet to get in and you need something to boost the weed control.”
Residual activity of dicamba makes all the difference, he says. Glyphosate has no residual.
NorthStar Genetics has two Xtend varieties available for this spring, NSC EXP 114 RR2X and NSC Starbuck RR2X.Caution
Dicamba is not strong on RR2Y canola.
“Dicamba will hold back, but it won’t control canola volunteers. You are going to need to mix dicamba with something else, maybe a product like Viper, to stop the glyphosate tolerant canola in your XtendiMax soybeans,” he says.
Froese warns, “The XtendiMax system has no cross-tolerance to any other Group 4 product. MCPA and 2,4-D will severely stunt the Xtend soybeans. It has the same mode of action but it’s a different chemical.”
Some adjustments for sprayers probably will be needed for the Xtend soybeans, he says.
“At grower meetings, we discuss everything on the label, advising them of things they need to be doing if they’re going to be successful,” he says.
For instance, pay attention to prevent drift and use Size 4 nozzles.
“We’re recommending extremely coarse to ultra-coarse droplet sizes, and don’t go so crazy-fast. All of our research has been done at rates of 10 gallons per acre. We recommend that you stay on label.”
He adds, “We want to make sure we minimize the accidents. XtendiMax will severely injure any soybean field that isn’t growing Xtend soybeans.”