Herbicides: Respect the Rotation

Bayer's landmark integrated weed management initiative focuses on the importance of herbicide diversity.

From an idea hatched by a Bayer product manager, Respect the Rotation™ quickly evolved into a new initiative with a three-day launch event with more than 200 participants from around the agricultural community. The program then embarked on a seven-city tour, evangelizing the power of diversity through rotation of crops, herbicide modes of action and herbicide-tolerant traits to advance efforts to preserve the utility of all herbicide-tolerant technologies.

Scientists have identified 358 resistant weed biotypes, including those resistant to glyphosate, PPO, ALS, dicamba and triazine chemistries. The rapid growth of Respect the Rotation is a testament to the urgency with which thousands of growers treat the issue of weed resistance. Over the last decade, a few salient facts have emerged in the widening war against weed resistance, not least the fact that glyphosate-resistant weeds are spreading at an alarming rate, from rampant infestations in the South to emerging populations in the Midwest. As reported by Weedscience.org, 358 biotypes have developed resistance to one or more herbicide groups, including glyphosate, PPO, ALS, dicamba and triazine chemistries.

The Roots of Resistance

Resistance stems from the continual use of single herbicide. The mode of action (MOA) within that singular herbicide, applied again and again to weeds, begins to exert tremendous “selection pressure” on the genetics of the weed, shifting the resistant populations within a field. Simply put, the weed’s survival becomes dependent on its ability to develop a way to elude the fatal effects of the herbicide’s active ingredients.

Researchers within the scientific community—including Crop Science—are actively pioneering new methods of combating herbicide resistance. Leading edge research even includes mapping the genetic codes of weed biotypes to better understand and respond to evolved resistance. As always, stewardship practices combining herbicide diversity and integrated weed management are an effective means of countering the evolutionary impact of weed resistance.

Researchers are actively pioneering new methods of researching herbicide resistance, including mapping the genetic codes of weed biotypes.

Smart Stewardship

Smart stewardship practices can help to preserve the utility of glyphosate technologies. Herbicide diversity is one such method, and Respect the Rotation was developed to popularize a three-step practice that provides opportunities for herbicide diversity:

  1. Rotate Crops – Crop rotation is a key component of the Respect the Rotation initiative, enabling herbicide diversity through the application of different herbicide modes of action across multiple crops.
  2. Rotate Herbicide-Tolerant Traits – Herbicide-tolerant traits allow producers to use over-the-top herbicides without harming crops.
  3. Rotate Modes of Action – Using herbicides with different modes of action is essential to reducing the selection pressure on resistant weeds. The more a single herbicidal mode of action is used on a field, the more selection pressure is applied to the targeted weeds, increasing the likeliness of resistant biotypes.

GlyTol trait, Bayer's new glyphosate-tolerant technology, has been field-tested with more than 20 major glyphosate herbicide formulations over the last five years, and seen excellent crop safety in all of them. When stacked with the LibertyLink® trait, it makes herbicide rotation easy. Bayer offers a number of solutions that are helping growers diversify on all three fronts, notably herbicide rotation. One of the leading alternatives to glyphosate technology is the LibertyLink® trait with Liberty® herbicide, which is the only nonselective alternative to glyphosate-tolerant systems and the most reliable weed management solution to glyphosate-resistant weeds. Liberty features a unique mode of action, allowing growers to reduce the selection pressure on weeds to develop resistance to glyphosate. LibertyLink is available for soybean, cotton, canola and corn.

In an industry first, Crop Science also recently launched a two-gene herbicide stack that combines the GlyTol® trait—glyphosate-tolerant technology that delivers flexibility and crop safety in cotton—and LibertyLink in high-performing FiberMax® cotton seed varieties. FM 9250GL offers full tolerance to both glyphosate and Liberty herbicides, providing growers with more flexibility within their weed management program.

For corn growers, Corvus® herbicide and Capreno® herbicide provide valuable rotation options. Corvus provides pre-emergent control of 50 weeds, including those resistant to glyphosate-, ALS-, PPO- and triazine-based herbicides, such as Palmer amaranth and waterhemp. With the longest-lasting residual of any post, Capreno controls more than 65 grass and broadleaf weeds, including those resistant to glyphosate, PPO, ALS, dicamba and triazine chemistries.

Collectively, the combination of crop, trait and mode of action rotation is proving an important foundation of Integrated Weed Management (IWM) strategies. To explore the recommendations of the Respect the Rotation program, contact your local Bayer sales representative or talk to your regional agronomist.

Works Cited

  • CropScience.Bayer.us. Bayer CropScience, 2010. Web. July 12, 2011.
  • Bayer CropScience. GlyTol Product Bulletin. Research Triangle Park: Bayer CropScience. n.d. Print.

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