Greensboro, North Carolina, USA
November 26, 2012
Setting the stage for a quality wheat crop and a profitable growing season hinges on the ability to effectively control competitive weeds. For more than two decades, weed resistance to individual families of chemistry has become commonplace, and this grueling challenge is not diminishing. With each growing season, previously successful herbicides with modes of action, like ALS and ACCase inhibitors, are becoming less effective against troublesome cereal crop weeds such as Italian ryegrass, green foxtail, kochia and wild oat. Aiming to keep this ever-growing issue top of mind, Syngenta visited with industry experts to give wheat growers topline tips to consider as they come face-to-face with weed resistance today.
Watch for Weeds
Herbicide resistance is the inherited ability of weeds to survive and reproduce following a herbicide application that would normally kill them. “If you overuse the same herbicide mode of action, you will face herbicide resistant weed species, and the severity will depend on the cropping system,” said Donn Thill, professor of weed science, University of Idaho. Fortunately, a proactive and diversified weed management strategy can help cereal growers stay ahead of resistant populations.
In the Pacific Northwest, winter annual grasses and some broadleaf weeds are top of mind for wheat farmers. “Growers fear them most as they’re the most difficult to control in wheat,” said Thill. “Such weeds include downy brome and prickly lettuce, as well as jointed goatgrass, for which we rely on Clearfield® herbicide tolerant wheat to help control,” he added.
To help address some of the most stubborn weeds and promote vigorous growth, Syngenta has also introduced its own line of Clearfield wheat varieties, such as AP604 CL, AP700 CL and SY605 CL, as a component of an integrated management solution. “Clearfield wheat technology allows the use of a Group 2 herbicide to be used in rotation with a Group 1 herbicide, like Axial® XL and Discover NG®, for resistance management in cereals,” said Don Porter, cereals technical brand asset lead, Syngenta. “The Clearfield technology, combined with imazamox, the active ingredient found in herbicides like Beyond®, is an excellent system to control stubborn weeds, such as jointed goatgrass and feral rye that are not effectively controlled by other selective cereal herbicides,” he added.
In the Northern Plains, recently noted resistant weeds include ACCase-resistant green foxtail and ALS-resistant kochia. “We’ve also been trying to manage and control ACCase-and ALS-resistant wild oat biotypes for several years now, and that’s the major concern today,” said Dr. Kirk Howatt, associate professor at North Dakota State University. “In terms of broadleaf weeds, the control we achieve is typically strong with products we currently have available for use in cereals, but we do have weeds like kochia that are becoming increasingly tolerant to various modes of action. We’re also seeing glyphosate resistance with ragweed and water hemp,” Howatt explained.
Howatt encourages keeping a close eye on weed species becoming increasingly tolerant to herbicides that once offered complete control, as well as evaluating a long-term strategy for greater return on investments over several years. “Preventive management solutions, or ‘the Cadillac treatment’ may cost more in the short-term,” he said, “but they help set the stage for a long-term gain and guard against potentially expensive problems before they occur.”
Start with a Competitive Crop
When problem weeds cannot be controlled by a previously effective herbicide, there is enhanced weed-crop competition for water, nutrients and light. “Weed scientists recommend growers use all the tools available to them in the most effective way possible,” Thill said. “The number one method of weed control is growing a competitive crop. If you begin with that, and you do all the right things to ensure the crop is aggressive and strong, weed control will be simpler to manage,” he added.
“Select the right varieties, plant at the right time and at the right depth, use the proper seeding rate and adjust for correct spacing – these agronomic practices can be followed by all growers to get the crop off to a healthy start.” In addition, seed treatments like Cruiser® seed treatment insecticide, Vibrance™ Extreme seed treatment fungicide and CruiserMaxx® Vibrance Cereals seed treatment insecticide/fungicide help ensure optimum root health, stand establishment, increased vigor, maximum yield potential, as well as offer protection against the trifecta of yield-robing diseases Rhizoctonia, Pythium and Fusarium in cereals.
Alternate, alternate, alternate
Over-reliance on the same herbicide mode of action is one of the key contributors to the growing problem. Experts say there is no substitute for alternating herbicides with different modes of action and chemical classes in the fight against resistance. “Yields can increase significantly with proper herbicide management,” said Howatt. “It’s unreliable and not recommended to cut labeled herbicide rates,” he added. For most effective management, be sure to use sequential applications and/or tank mixtures of herbicides with different modes of action; apply herbicides at the full label rate and at the proper growth stage; extend the range of available herbicides by employing a diverse crop/fallow rotation; and prevent weed escapes from producing seed by controlling weeds early on.
Scout with a Watchful Eye
There is also no substitute for careful, timely observation and scouting to keep resistant weeds from spreading. Be sure to clean tillage, seeding and harvest equipment when leaving fields with herbicide-resistant weeds to keep them from moving to other acres. “Be familiar enough with your fields to catch resistant biotypes early, and be aware of minor or major changes, like green streaks where seed has fallen,” Howatt said. Awareness of field history and yield impact, a watchful eye and a proactive management program will help growers save money and hassle in the long run.
Rotate Crops and Think Tillage
Cultural management options to help thwart resistance are tillage and crop rotation. Cereal crops rotated with crops like buckwheat, clovers and/or alfalfa can help keep weeds from adapting to a certain environment, making more control options available. These crops obstruct weeds, release natural weed-killing chemicals and simultaneously improve soil structure, prevent erosion and offer crop nutrients.
While no-till systems improve soil health and save farming costs, they can also enable perennial weeds to flourish. Howatt recommends delayed seeding to ensure adequate time to kill weeds with a burndown herbicide first.
To help meet the challenge, Syngenta has a diverse portfolio of cereal herbicides to meet the weed control needs of each field and help farmers grow more wheat. To help avoid additions to the seed bank, consider a burndown like Touchdown® brand herbicides in addition to an in-season application of a postemergence herbicide like Axial XL or Discover NG. “Axial XL will typically provide the best control for wild oat, and is likely still controlling these resistant populations,” said Howatt. “It is still critical to rotate to other herbicides so that it remains effective,” he added.
Cross-spectrum Axial Star and Sierra™ herbicides are recent additions to the Syngenta herbicide portfolio and control a broad spectrum of grass weeds and several key broadleaf weeds, with tank-mix flexibility to customize broadleaf weed control on a field-by-field basis. “Sierra has been a great resistance management tool in North Dakota for residual control of late-emerging foxtails and downy brome,” said Josh Messer, agronomist, Plains Grain and Agronomy. “It offers wheat growers a way to manage ACCase-resistant grass weeds like wild oat, as well.” Serving as another tool for sound grass herbicide rotation is Foxfire® herbicide, designed specifically for Northern Plains to control foxtails, as well as wild and volunteer oats and barnyardgrass.
As a leader in resistance management solutions and strategies, Syngenta has made it a standard practice to include management information and the mode of action group number on its product labels to help growers remain ahead of resistance. As winter 2012 sets in and planning begins for the next growing season, remember that diversity is key in any resistance management program. Refrain from heavy reliance on any one method of control to set the stage for strong, robust crops and profitable returns for years to come.
©2012 Syngenta. Important: Always read and follow all bag tag and label instructions before buying or using Syngenta products. The instructions contain important conditions of sale, including limitations of warranty and remedy. CruiserMaxx Vibrance Cereals and Vibrance Extreme are not currently registered for use or sale on all crops in all states. Foxfire is currently registered for use only in: Minnesota, Montana, North Dakota, South Dakota and Wyoming. Some crop protection products and seed treatments may not be registered for sale or use in all states or counties. Please check with your state or local extension service before buying or using Syngenta products. Axial®, Cruiser®, CruiserMaxx®, Discover®, Foxfire®, Sierra™, Vibrance™, Touchdown® and the Syngenta logo are trademarks of a Syngenta Group Company. Beyond® and Clearfield® are trademarks of BASF Corporation.
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