Glyphosate has undoubtedly been the herbicide of the century: Due to its flexibility in use, high degree of effectiveness and lack of soil residual activity it was very simple to use. In the mid-1990s, glyphosate tolerant corn, cotton and soybean varieties revolutionized agriculture as their use exploded in the marketplace, first in the USA, and later in South America. “The glyphosate-tolerance trait meant that you did not need a pre-emergence herbicide,” says Dr. Harry Strek, Bayer CropScience Head of Integrated Weed Management and Resistance Biology. “Farmers could spray right into the crop canopy once or twice and they only had to buy ONE product. It was as easy as pie.”
There seemed nothing more to say about herbicides and many companies abandoned or seriously curtailed herbicide research as a consequence. But nature struck back with a vengeance by developing glyphosate resistant plants such as the astonishing Amaranthus palmeri (Palmer amaranth). This “super weed” threatened the harvest with its size (up to three meters), its alarming seed production rate (up to a million seeds per plant) and its ability to transfer resistance genes among related Amaranthus species. “The resistance problem exploded in 2009,” recounts Chuck Farr, independent crop consultant in the US State of Arkansas. “It was unbelievable. We worked non-stop. But I really loved it. We were working as real advisors again, offering the farmers much needed advice on effective alternatives and sustainable strategies.”
Prevention is better than cure
Managing herbicide resistant weeds such as Palmer amaranth, Chuck Farr recommended his growers use glufosinate-ammonium-based herbicides in concert with LibertyLink® crops, presently the only non-selective alternative to glyphosate tolerant systems. Containing a glufosinate-ammonium tolerance trait, a LibertyLink crop allows rotation of the herbicidal mode of action in cotton, canola, soybeans and corn. In the near future, Chuck Farr will hold an additional trump card in his hand: New double-stack seeds with combined traits for glufosinate-ammonium and glyphosate to manage resistance with two different herbicide classes.
“Our goal is the sustainable activity of herbicides,“ says Harry Strek. “We want to get more glufosinate-ammonium out into the market which will contribute to saving glyphosate.”
In the years to come, resistance prevention and management will play an ever increasing and important role on a global scale. As a result, the herbicide business will become more complex, resulting in a greater need for professional advice and explanation. “Recommending the right strategy for integrated weed management requires intimate knowledge of the many different factors that interact in the field and that vary from farm to farm,” says Dr. Martin Hess, Integrated Weed Management and Resistance Biology. “This is why the Bayer CropScience sales representatives see their role as going far beyond just selling plant protection products. Monitoring the well-being of a farm, they play a role similar to that of a family doctor in human medicine.”
Like a good family doctor, they know the agronomic history of the farm and the personal farming style of the owner. Identifying early spots of resistance, they can support the farmer in developing a preventive strategy. “At the end of the day, it is always better – and cheaper – to spend money on prevention rather than wait for resistance to strike,” says Martin Hess.
What then, are the components of an effective prevention strategy? “Diversity is the key,” says Joachim Kaiser, Integrated Weed Management and Resistance Biology. “Planting the same crop repeatedly and partnering it always with only one single herbicide, gives the weeds ample time to adapt to the same treatment year after year, until it become resistant to a particular herbicide or mode of action. That is why the fight against resistance always focuses on providing variety.” The selection pressure can be reduced by crop and chemical rotation, for example by scheduling a summer crop, if primarily growing winter crops, and alternating different herbicidal modes of action during the season. Deep tillage helps to reduce the seed bank in the soil and keeps the seeds of some problem weeds like Palmer amaranth from germinating in huge numbers, covering the surface like a green carpet. Delayed planting times can also make a difference: If the weeds have time to germinate after ploughing and before sowing, they can be controlled either mechanically or with an herbicide.
Exploring the secrets of resistance
If worse comes to worse and the weed resists a treatment, the time has come for the family doctor to consult a specialist. The Bayer CropScience sales rep turns the case over to the diagnostics team in Frankfurt/Main (Germany), asking them to detect the cause of the herbicide failure. The required analyses are performed in a state-of-the-art laboratory which Bayer CropScience set up staffed with specialists and specialized analytical instruments. Located in the company’s herbicide biology and phytoregulator research institute, it offers a special service: Identifying in detail the components of a weed’s individual resistance profile, the team provides the diagnostic equivalent of a “blood analysis” for weeds suspected of being resistant to herbicides.
Today, hundreds of samples sent by courier containing live weeds arrive for analysis in Frankfurt every year. Each sample is an urgent cry for help; someone out there needs to know what the verdict is: Is it really a case of resistance? If so, what type of resistance is it, and how many modes of action are affected? Which herbicides are still effective? What shall I spray in the coming season?
This state-of-the-art emergency analysis is supported by the traditional diagnostics in the greenhouse, where weeds are grown from the seeds of the previous season. Testing the weeds for resistance under real-life conditions allows the team to fine-tune herbicide mixtures for the coming season.
Out there in the field, the Bayer CropScience sales representatives connect all the information that is now available: the detailed resistance profile, the greenhouse diagnosis, and their own long-term knowledge of the individual farm. This allows them to work out a specific customized strategy for the individual needs of the farmer. Next to the rotation of crops and herbicides, tillage practices, and altering planting times, their recommendations might also include certain other assorted precautions, such as cleaning harvesters between fields or to make sure that neither machines nor boots transfer the resistance from one field to the next.
Expanding the arsenal
Stricter registration legislation and a declining number of companies engaged in herbicide research mean that the range of herbicides is declining, while resistance is advancing rapidly on a global scale. That is just one of the reasons that Bayer CropScience is committed to staying in the business and fighting this trend. To strengthen its basis the company plans to further expand its research activities.
Bayer CropScience herbicide researchers are busy identifying resistance trends as they develop and focusing on finding resistance busters – new molecules with novel modes of action to fight problem weeds. Simultaneously, Bayer CropScience is investing significant resources into safener research to ensure that herbicides with marginal selectivity but an extremely interesting weed control spectrum will be marketed in the future. Selectivity research identifies both protective safener substances and herbicide tolerance traits, two completely different mechanisms that immunize the crop against the herbicide, thus expanding the application range of new and old herbicides.
Today, the company’s research effort has results to show: “In the past few years, we have launched more herbicides than our competitors,” says Harry Strek. “We are the leading company in safener research and our research pipeline is brimming.” For Chuck Farr and his Arkansas colleagues there is also another trump card in the offing: As of 2015, Bayer CropScience plans to launch a triple-stack soybean variety. A co-development of several partners, the soybean is immune to both glyphosate and glufosinate-ammonium, and to a third mode of action – the herbicide class of HPPD inhibitors (e.g., Laudis®, Balance® and Husky®). Combining tolerance to three separate modes of action in one seed is a strategy that should certainly do the trick of bringing resistant weeds to their knees – including some pernicious species of the future.
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