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Herbicide resistance - how weeds are fighting back

The threat posed by herbicide resistance to global crop production systems is increasingly being recognised by researchers, farmers, and regulatory bodies alike. More and more, the possibility of a world in which farmers have little or no options when it comes to controlling weeds is becoming a reality.


Herbicide resistance was first formally documented in the 1950s, though the phenomenon was likely around before then. Regardless, as a result of increased selective pressure caused by the uptake of herbicides in the intervening decades, resistance has boomed. At the start of 2021, more than 250 weed species have been confirmed to exhibit resistance to at least one herbicide mode or site of action around the world, affecting more than 90 crops in 71 countries. 


The challenges presented by herbicide resistance are manyfold. Some weeds present a danger to livestock or humans trying to remove them, whilst other invasive species may pose a threat to local plant life. Resistance can put financial pressure on farmers, too, forcing them to invest time and money sourcing new weed management practices, or else face a continuously declining crop yield.


Viewed over the long term, though, the risks go beyond the realm of economics - as the global population approaches 8 billion, food scarcity borne as a result of herbicide resistance is liable to represent an increasingly significant threat.


Science for a safer world


Our extensive Dr. Ehrenstorfer portfolio encompasses a wide variety of herbicide and metabolite reference materials in different formats, tailored to meet your specific needs.


Plus, our range of metabolites and stable isotopically labelled reference materials enables further comprehensive testing and screening, all of which allows your laboratory to achieve results you can rely on.



The root of the problem 


Herbicide resistance often develops as a result of specific weed control programmes, which provide concentrated selective pressures for the development of resistance. Increasing the diversity of weed management practices can help to slow the development of herbicide resistance and reduce its adverse effects on crop yields. Genes that enable weed species to resist herbicides are present in all weed populations, but as a weed management system diversifies, the odds of any single weed ‘passing through the net’ diminish.


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For an example of the dangers of investing too heavily in a single weed management system, we need look no further than the headline-dominating herbicide glyphosate.


Case study: glyphosate


Glyphosate was something of a ‘wonder herbicide’ for growers urgently needing a strategy to combat widespread resistance to most commonly used selective herbicides. Glyphosate made weed management simple and efficient, controlling a wide range of weeds at multiple application timings. By 1997, the herbicide was the most widely-used in the world, accounting for 11 percent of global herbicide sales.


However, the intensive use of glyphosate and simultaneous decline in the use of other herbicides lead to the widespread evolution of glyphosate resistance in weeds. One of the first examples of this was a population of goosegrass in Malaysia in 1997 - just eight years later in 2005, ten other instances of resistance had been reported around the world. Today, these resistant weeds are threatening current crop production practices.


Resisting the tide


Monitoring and mitigation are powerful tools when it comes to managing herbicide resistance. Effectively monitoring weed populations enables the early detection of resistance, allowing steps to be taken quickly to reduce its impact. Because of factors like seed dormancy, eradication is generally not feasible - a good mitigation strategy focuses instead on the implementation of best management practices to help prevent further spread and development.


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Herbicide resistance testing allows the identification of herbicide susceptibility for particular weeds.


Another tool in the weed management toolkit is herbicide resistance testing, using either pot or Petri-dish assays to test seeds collected from weeds which survived herbicide treatment in the field. 


It’s usually more effective for analysts to focus on determining herbicide susceptibility, rather than resistance, in order to figure out an effective herbicide strategy. Resistance testing allows for:


-       the identification of herbicide susceptibility for particular weeds

-       the avoidance of wasteful use of herbicides, saving money and time, and limiting environmental damage

-       the long-term monitoring of the efficacy of resistance management strategies. 


Case study: Amaranthus tuberculatus - the perfect weed?


Known by a number of names including common waterhemp, tall waterhemp, and rough-fruited amaranth, Amaranthus tuberculatus is a summer annual broadleaf that has been reported as a weed in no fewer than 40 U.S. states. 


Because of its long germination period, a single herbicide application is unlikely to prove effective against Amaranthus tuberculatus. Furthermore, the genetic diversity within a waterhemp population, itself a product of the plant’s dioecious reproductive system, increases waterhemp’s potential for evolving novel herbicide resistances.


Waterhemp has evolved resistance to a multitude of herbicides, including triazines, ALS inhibitors, PPO inhibitors, glyphosate, HPPD inhibitors, and 2,4-D. The plant’s prolific capacity for developing resistance has led to some scientists calling Amaranthus tuberculatus the perfect weed’.



At LGC, we’re committed to supporting scientists fighting back against the threat of herbicide resistance. That’s why we’ve recently updated our portfolio of herbicide and metabolite reference materials, which now numbers more than 1100 products to help your laboratory perform accurate testing, including phenoxy herbicides, triazines, ALS herbicides, and HPPD inhibitors.


Recent additions to the range include: 

Carfentrazone (free acid) 100 µg/mL in Methanol

Dimethachlor metabolite CGA 369873 sodium

Orthosulfamuron 100 µg/mL in Acetonitrile

Atrazine-desethyl-desisopropyl 100 µg/mL in Acetonitrile

2,4-D 1000 µg/mL in Acetone

Aminocyclopyrachlor 100 µg/mL in Acetonitrile

Clethodim-sulfoxide 100 µg/mL in Acetonitrile

MCPA sodium 100 µg/mL in Acetonitrile:Methanol

Bicyclopyrone 100 µg/mL in Acetonitrile

MCPA-dimethylammonium 100 µg/mL in Acetonitrile

Tefuryltrione 100 µg/mL in Acetonitrile


Pentoxazone 100 µg/mL in Acetonitrile

Metolachlor metabolite CGA 49751

Metazachlor metabolite BH 479-12


Visit our website or get in touch today to find out how we can assist you in your quest for reliable, accurate results.


Discover Herbicides

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