Jan. 25, 2016
“How many of you think the new herbicide-tolerant crops and the appropriate herbicides will fix herbicide-resistant weed problems?”
A stony silence followed, accompanied by motionless hands in a sea of agronomists and crop consultants attending last month’s ISU’s Integrated Crop Management Conference. That says a lot about how farmers should approach future corn and soybean weed management. Sure, there are some great new herbicide-tolerant systems coming. Two are initially slated for 2016.
• Dow AgroSciences’s Enlist Weed Control System confers herbicide tolerance to 2,4-D choline and glyphosate in corn and soybeans and “fop” herbicides in corn.
• Monsanto’s Roundup Ready Xtend Crop System includes tolerance to glyphosate and dicamba in crops including soybeans.
Following are two herbicide-tolerant systems slated for later this decade.
• The Balance Bean GT Soybean Performance System from Bayer CropScience, MS Technologies, and Mertec LLC is slated for a full-scale launch in 2017, pending regulatory approval. It pairs up trait tolerance to glyphosate with an isoxaflutole-based herbicide (HPPD-inhibitor site of action) like Balance Flexx in corn. The system’s herbicide will be called Balance Bean.
• An effort by Bayer and Syngenta will confer tolerance to isoxaflutole and mesotrione on soybeans. Mesotrione is another HPPD-inhibitor site of action now featured in the corn herbicide Callisto. This product is slated to debut later this decade.
Following are updates on new herbicide-tolerant systems and steps you’ll need to take to manage weeds in the future.
1. What’s Up With Enlist Duo?
A 2010 trip to Tennessee to pick up a tractor he purchased was an eye-opener for Todd Hanten of Goodwin, South Dakota. That’s when he saw how Palmer amaranth was crippling that state’s soybean production.
In 2011, Larry Steckel, University of Tennessee Extension weed specialist, calculated that glyphosate-resistant weeds like Palmer amaranth were costing Tennessee soybean farmers $120 million annually.
“It was just a scared, sick feeling,” says Hanten. “I couldn’t believe the Palmer amaranth infestations were that bad. These weeds will be tough to control without new weed-control technologies.”
That might be a while. Dow AgroSciences was set to fully launch its Enlist Weed Control System this year once China granted import approval. In late November, though, the EPA petitioned the Ninth Circuit Court of Appeals to revoke registration for Enlist Duo, the herbicide component of the Enlist system.
The EPA cited concerns about potential synergy between 2,4-D choline and glyphosate adversely impacting endangered plants. EPA stated these claims were made on patent applications for Enlist Duo. Dow officials say this occurred in a patent application unrelated to the actual product that was registered.
New information could lead EPA to adopt different restrictions for use of Enlist Duo, but still permit its use. Under the initial registration, a 30-foot downwind border was mandated between a field where Enlist was applied and the surrounding area. It’s possible this buffer area could adjusted to further prevent any impact on adjacent and/or endangered plants, according to EPA statements. Dow officials say they are cooperating with EPA and remain optimistic about a 2016 Enlist system launch.
Based on the data package Dow submitted to EPA, Owen believes safeguards exist to prevent adverse impacts on bordering endangered plants. Still, a full-scale commercial Enlist system launch may take a while.
“It may be a long, drawn-out discussion in court,” points out Owen.
2. The Other Potential 2016 Entrant
The other herbicide-tolerant system in the gate for 2016 –pending regulatory approval for the herbicide component– is Monsanto’s Roundup Ready Xtend Crop System. It teams Roundup Ready 2 Xtend soybeans with tolerance to glyphosate and new dicamba formulations. Monsanto’s herbicides for this system include Roundup Xtend, a glyphosate-dicamba premix. Roundup XtendiMax is a stand-alone dicamba formulation. BASF’s Engenia herbicide is another dicamba herbicide that can be used in the Roundup Ready Xtend Crop System.
3. The New 2,4-D and Dicamba Formulations Work
Your parents or grandparents may remember the days when they’d cover tomato plants in their gardens when a synthetic auxin like 2,4-D was being applied nearby. Off-target movement has always been the knock against 2,4-D and dicamba.
Still, the new formulations really work to reduce off-target movement potential. Dow officials say the Enlist Duo herbicide that contains 2,4-D choline has 87% and 96% reduction in volatility compared with existing 2,4-D amine and 2,4-D ester formulations, respectively. Meanwhile, Enlist Duo cuts drift potential 90% compared with older 2,4-D formulations when applied using low-drift-potential nozzles, say Dow officials.
“I was impressed with the Enlist Duo,” says Hanten. “I had non-2,4-D tolerant soybeans planted next to Enlist corn in 2015, and there was no drift at all.”
Meanwhile, BASF officials say its Engenia dicamba herbicide features low volatility. Monsanto officials add its dicamba formulations contain the proprietary VaporGrip technology that reduces dicamba volatility when compared with existing dicamba formulations. “They have made a believer out of me,” adds MU’s Bradley.
Still, any herbicide can move off-target, given certain weather conditions, says Bradley. So stick to herbicide label directions for when you can apply. Use low-drift nozzles stated on the label. Spray away from sensitive crops.
“When you apply something in a 30-mph wind, it will blow,” says Aaron Hager, University of Illinois Extension weed specialist.
Remember this, because . . .
4. Spray Windows Are Tight – Really Tight
A wind speed of 3 to 10 mph is often the sweet spot when it comes to spraying herbicides, says Mark Hanna, ISU Extension agricultural engineer. Drift potential rises above 10 mph. Still conditions below 3 mph can trigger movement via volatility.
Trouble is, that window is a lot tighter than you think.
Jason Norsworthy, University of Arkansas weed specialist, analyzed 2010 to 2012 Arkansas State Plant Board’s weather records for Mississippi County in northeastern Arkansas.
He examined five-minute periods from 7 a.m. to 7 p.m. when wind gusts did not exceed 10 mph but were more than 3 mph to minimize inversions.
Although this was just one part of Arkansas, similar tight application windows exist just about everywhere.
That’s why when conditions are right, you have to be ready to spray because . . .
5. Weeds Grow Quickly
Back in 1993, ISU weed scientists Andrew C. Seibert and R. Brent Pearce published a Weed Science journal article noting that waterhemp can grow 1 inch per day. If the herbicide label states waterhemp should be controlled at a 4-inch height, just a day’s delay can mean the difference between control success or failure.
“You have to be aggressive with applications,” says Bill Johnson, Purdue University Extension weed specialist. “If you figure out you have a problem in the morning, you’ll need to be ready to spray in the afternoon. That’s how quickly waterhemp grows.”
6. Preemergence Herbicides Buy Time
One way to set back rapidly emerging weeds is to apply a preemergence residual herbicide.
Joe and Rollin Primus have applied soybean preemergence herbicides like Zidua and Fierce. “They hold down the weeds pretty well,” Joe says.
This buys time for the crop to canopy and reduces weed pressure for later-applied postemergence herbicide applications. Granted, even the best of these wear off after 45 to 60 days. Still, they pay.
“There was a night-and-day difference between farmers who used residual herbicides on soybeans last year and those who did not,” says Dave Phelps, a BASF innovation specialist. “Farmers without residuals had disastrous levels of weeds like waterhemp that we can’t seem to control.”
7. Pair Herbicides With Cultural Practices
Is your 30-inch row planter nearing its life’s end? A switch to a narrow-row planter can also help create an earlier canopying crop that smothers weeds.
Ditto for incorporating a grass crop like wheat into your row-crop rotation. This can throw weeds accustomed to row crops off balance and forestall herbicide-resistant weeds.
Then there are those scattered weeds or patches of weeds that surface in your fields late in the season. If you can, rogue them out of the field prior to harvest. They could be herbicide-resistant.
“Those little patches can go through the back of the combine and become rather large patches the next year,” says Owen. “At the very least, drive around them during combining and finish those areas at the end so you don’t spread weeds all over the field.”
8. Mix It Up
Apply on weeds 4 inches or smaller. Use full rates. Apply a preemergence residual in advance of a postemergence herbicide.
These are some of the steps that BASF recommends for Engenia, its new dicamba formulation for Monsanto’s Roundup Ready Xtend Crop System. However, these recommendations could apply for most any nonselective postemergence herbicide.
“We do not want to repeat the mistakes of the past,” says Chad Brommer, BASF Engenia technical marketing manager.
Shaving rates, delaying postemergence applications, and nixing preemergence residual herbicides are reasons herbicide-resistant weeds result in the first place. Following label instructions can snuff these mistakes.
9. PPO Inhibitor Is the New ‘It’ Resistance
When it comes to weed resistance, ALS-inhibitor and glyphosate resistance are so yesterday compared with PPO-inhibitor resistance.
“That is what I am seeing over and over again,” says Purdue’s Johnson. Like other herbicide sites of action, this resistance is spurred by repeated applications of PPO inhibitors.
PPO-inhibitor herbicides like Flexstar and Cobra remain excellent tools. Still, repeated reliance on PPO inhibitors and increasing herbicide-resistant waterhemp populations means weed resistance will worsen. Bob Hartzler, an ISU Extension weed scientist, calculates that waterhemp resists one more herbicide site of action every 3.7 years.
“We are burning through the pile pretty quickly,” says Owen.
10. Nothing Truly New Is Coming
Every year, sales representatives of agricultural chemical companies extoll the virtues of new corn and soybean herbicides.
When the shiny veneer of marketing spin is stripped away, though, just new formulations or combinations of existing herbicide sites of action result. The last truly new corn and soybean herbicides were HPPD inhibitors that debuted around 20 years ago.
“These existing sites of actions in many cases have resistance in existing weed populations,” says Owen. “Even if one was discovered today and there was the investment capital behind it and it met regulatory hurdles, it would be at least 10 years before it became commercially available.”
No agricultural chemical company has announced a corn and soybean herbicide with a new site of action that will soon appear on the market.
This doesn’t mean the new herbicide premixes and formulations are worthless. It does mean, though, that they aren’t the sole answer to your weed problems. Ditto for any upcoming herbicide-tolerant weed-control systems. Thus, weed management through cultural practices remains equally important.
“Herbicides will not solve this problem by themselves,” says Owen. “They are good tools to a point, but they won’t fix the problem of resistant weeds.”
By Gil Gullickson, Crops Technology Editor
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