No Delay to Fight Against Weed Resistance

Editor's Note: With the continuous use of herbicide, over recent years more and more weeds become resistant to herbicides. Due to the difficulty in weed control, farmers have to use larger dosage of herbicide, which result in emergence of "superweed" in some regions. Now weed resistance is not only a tough issue for farmers or herbicide producers but has grown to be a global issue, which is becoming more and more serious. The emerging resistant weed not only makes farmer's weed control difficult and more costly but also raises a challenge to herbicide producers as how to work out effective and sustainable solutions. To this end, we presents the information based on an organized discussion participated by 3 multinationals who are excellent in performances of pesticide research and resistance management - Syngenta, Bayer CropScience and Dow AgroSciences. Via this discussion readers are able to understand the information of evolution of global weed resistance and the latest solutions available from these multinationals. We want to take this opportunity to express special thanks to Dr. Harry Strek, the Head of the Bayer CropScience Weed Resistance Competence Center, Dr. Mark Peterson, the Global Biology Leader for the Enlist Weed Control System of Dow AgroSciences and Syngenta for joining the discussion.

Evolution of global weed resistance

Since the finding of the 2,4-D resistant Daucus carota and Commelina diffusa in Canada and the US in the 1950’s, the resistance of weed has grown with the global agriculture all the time. As shown by the statistical figures (Table 1) of International Survey of Herbicide Resistant Weeds, it can been seen that in the beginning 20 years resistance of weed grew rather slowly but started to grow quickly following the rapid global pesticide growth since the mid-80’s last century.

According to the census of International Survey of Herbicide Resistant Weeds conducted by Herbicide Resistance Action Committee, up until 1st February 2015, there are currently 445 unique cases (species x site of action) of herbicide resistant weeds globally, with 242 species (142 dicots and 100 monocots). Weeds have evolved resistance to 22 of the 25 known herbicide sites of action and to 156 different herbicides. Herbicide resistant weeds have been reported in 85 crops in 66 countries.

Table 1 shows that the US is the most seriously weed resistanceaffected country with 150 species ranking No. 1; Australia and Canada rank No. 2 and No. 3 respectively. The total number of resistant weeds which emerged in 66 countries has amounted 922 species. Up to the end of October 2010, the total number was 672 showing the fast-speed growth of resistant weeds.

If calculated by the resistance to different sites of action, the weeds which are most resistant to the herbicides of different sites of function are by ranking respectively the Lolium rigidum, Echinochloa crus-galli, Poa annua, Alopecurus myosuroides and Eleusine indica; if calculated by the number of resisted herbicide varieties, the most resisted herbicides are by ranking respectively the atrazine, imazethapyr, tribenuron-methyl, imazamox, chlorsulfuron, metsulfuron-methyl and glyphosate.

The harm of resistant weeds and the difficulties at present

The harm of resistant weeds can be summarized as the following: farmer’s forced change of weed control and crop management practice, increased cost of weed control, reduced herbicide choice and decreased yield as well as loss of income for farmers.

According to Bayer CropScience, in the US, 57% of farmers reported one or more glyphosate resistant weeds on their farms in 2014, up from 44% in 2012 and 51% in 2013 (source: Stratus Ag Consulting). In Europe, mainly cereal crops are affected by resistant weeds such as blackgrass, silky bent grass, wild oats and ray grass. In some regions of the UK, control of blackgrass has become critical in winter wheat, and the cost of weed control has more than doubled over the past few years.

Pesticide producers and farmers have presently realized the harm of resistant weeds and its rapid growing trend, and have tried effort to solve the problem, but a lot of realistic problems do exist. For example the continuously growing number of resistant weeds globally, growing number of multi-herbicide resistant weeds, growing cultivated land affected by resistant weeds, the constantly growing resistant weeds against glyphosate which is of the largest herbicide quantity currently used in the world. Though resistance has not led to the total loss of any one herbicide, yet the way of use of pesticide of farmers and producers has changed indeed. What is finally most disappointing is that herbicide of new mode of action has ever been developed over the last 20 years, which means weed control will still have to rely on existing herbicide varieties.

“Many crop science companies have significantly reduced or even stopped their herbicide research since the late 1990s. Industry-wide, there was a sharp decrease in patent applications for herbicide active ingredients, from 250 per year in 1990 to approximately 50 – 100 applications in recent years. While investment into new herbicide mode of actions is picking up again, a significant gap has to be bridged: No new mode of action significant for the world market has been launched in over 20 years, and due to development timelines of 10+ years from discovery to market introduction for a new compound, no new herbicide mode of action will be launched in the next 8 years,” said Dr. Strek.

Principles of managing herbicide resistance & companies’ solutions

An optimum control measure would be the diversified practices, which include the use of different herbicides or herbicides of different mode of action. Non-chemical diversified weed control practices include crop rotations, soil cultivation, post-harvest weed seed control and other measures. “It is well known that a diversity of product recommendations will be important to provide answers to the marketplace as no one product can do it all”, said Dr. Mark Peterson of Dow AgroSciences.

Bayer CropScience – Innovation & farmers training

Dr. Strek said that, “the tools that form the basis of Herbicide Resistance Management are based upon diversity. For this reason, our global campaign Diversity is the Future and local programs like Respect the Rotation in the US, the Black-Grass Task Force in the UK or Diversity Can’t Wait in Australia promote diversity in herbicides, in modes of action, in crops, in herbicide tolerance traits, as well as in non-chemical weed management practices.”

“Bayer CropScience offers integrated solutions for weed management. We enhance productivity by providing an understanding of weed resistance problems and developing solutions, searching constantly for innovations, and expanding partnerships with leading universities and institutes. We look intensely at problems to get a handle on how resistance is developing. Weed resistance is a global problem, but in order for solutions to work, they must be carried out locally. The scientists and specialists employed at our Weed Resistance Competence Center in Frankfurt, Germany, test and develop new solutions to manage resistance and share our knowledge with the international agricultural community. Currently, the center has focused on resistance projects in 44 countries across Europe, North and South America, Australia, South Africa and Asia Pacific. In the US we
are investigating population genetics and resistance mechanisms in Palmer Amaranth, a particularly difficult-tocontrol weed, and in Australia metabolic resistance in Lolium (ryegrass). Looking ahead, the WRCC plans to further broaden cooperation and dialog with external partners. In terms of innovations, Bayer CropScience is strongly committed to discovery research and stands out as the agricultural company with most herbicide patent applications in 2013. Our existingMproduct portfolio includes high-performing seeds with built-in herbicide control technology (e.g. LibertyLink®), superior crop protection products with renowned brands such as Atlantis®, Huskie® and Adengo®, as well as tailored services and stewardship measures.” Strek added.

Syngenta – promotion of diverse agronomic practices

Syngenta has extensive stewardship efforts to promote the use of best weed management practices to delay the onset of resistance. This includes working with university research and extension units and developing premixes of key herbicides in corn, soybeans and cotton. We have been targeting the evolution of weed resistance on many fronts with our integrated weed management offerings and technical expertise (e.g. Gramocil: soy (Brazil); Halex GT: corn (U.S.); Prefix: soy (U.S.).

Syngenta believes that resistance management will be achieved locally through the promotion of diverse agronomic practices and with combinations of new and proven chemistries. This means that multiple lines of defense are needed. New herbicide tolerant crops - when introduced - will be offered as part of sustainable “farmer first” agronomic programs. It is vital that growers are informed about IWM (Integrated Weed Management) and take action.

Dow AgroSciences – committed to sustainable solutions

Dow AgroSciences, as a researchbased company, is always looking for innovation to address market needs, and resistance management has been a priority for many years as nature continues to adapt. Sustainable solutions are at their best when a diverse system of weed control is in place. “For example, our new Enlist™ Weed Control System brings multiple modes of action to bear on resistant and hard-to-control weeds. Several other examples of products that are helping farmers fight resistance include Arylex™ active, which has a different target site within the auxin mode of action, as well as a new broad-spectrum herbicide we are bringing forward,” said Dr. Peterson.

 “Meanwhile, Dow AgroSciences focuses on providing recommendations that enable a product to be an option for farmers for a long time. As part of that effort, product stewardship has been and will continue to be an important focus as we work with customers and other stakeholders to ensure proper product use.”

“Our stewardship efforts for the Enlist system around the world illustrate Dow AgroSciences’ commitment to helping our customers know how to best use our products to avoid resistance. Education and interaction are essential to our approach in launching any product. For example, we developed an Enlist™ Ahead app which offers growers and applicators vital herbicide application information from a single source. The app, designed for use with the Enlist Weed Control System, is a precision agriculture tool for maximizing weed control performance, managing weed resistance and making responsible applications of Enlist Duo™ herbicide with Colex-D™ Technology,” Peterson added. “It is important to work on products for the future, and it is also essential to work with customers today to be sure each season is one where farmers are making progress to deliver the crops needed by a hungry world in a sustainable manner.”