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Balancing steel and herbicides to reduce resistance – why resistance?

Balancing steel and herbicides to reduce resistance – why resistance?. Micheal D. K. Owen Iowa State University Ames, IA 50011 USA mdowen@iastate.edu www.weeds.iastate.edu. Herbicide resistance = superweeds ?.

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Balancing steel and herbicides to reduce resistance – why resistance?

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  1. Balancing steel and herbicides to reduce resistance – why resistance? Micheal D. K. Owen Iowa State UniversityAmes, IA 50011 USA mdowen@iastate.edu www.weeds.iastate.edu

  2. Herbicide resistance = superweeds? • While this “description” draws considerable attention (i.e. NY Times), it is clearly incorrect and inappropriate! • Organisms adapt to the selective forces that exist • Plants have impacted man since the transition from hunter/gatherer to an agrarian society – approximately 8 millennia

  3. Superweeds? Evolution does not work that way!

  4. Major weed shifts in Iowa ? ? ? ? ? ?

  5. Herbicide resistance – a historical perspective • Concern for herbicide-resistant weeds predates glyphosate by more than 50 years • The USA has a long history of herbicide-resistant weeds • Triazine resistance and ALS resistance are currently most common • Globally, resistance evolved for ~21 herbicide MOAs in 201 weed species represented by 372 weed biotypes* *www.weedscience.com

  6. Evolution of glyphosate-resistant weeds* *www.weedscience.com

  7. Glyphosate-resistant weeds found in Iowa Giant ragweed Common waterhemp Horseweed Marestail

  8. Ohio Weed Gothic (a study in giant ragweed)* *with apology to Grant Wood

  9. Evolution of herbicide resistance in common waterhemp *www.weedscience.com

  10. Soybean in a common waterhemp field

  11. “Causes” of herbicide resistance • Herbicides do not “cause” weeds to evolve resistance per se • How herbicides are used “causes” weeds to evolve resistance (e.g. management) • Factors to consider • Frequency of the resistance trait in weeds • “Effectiveness” of the herbicide • Management strategies • Others (e.g. herbicide marketing)

  12. Original population – year 1

  13. 99% Control - Population still appears like the “original”

  14. Year 2+ - Adapted biotype quickly becomes the dominant weed Year 4 with the same weed management program

  15. Poor control – the weed population shift is obvious and a serious problem

  16. Herbicide resistance • The evolution of herbicide resistance is not a herbicide problem • The evolution of herbicide resistance is not a trait problem • The evolution of herbicide resistance is not a glyphosate problem • The evolution of herbicide resistance is a behavioral problem

  17. Integrated Weed Management Mechanical Cultural Cultural Mechanical Herbicides Herbicides Future Current

  18. Conclusions • Weeds have and will inevitably adapt to what mankind provides, irrespective of technology • Current issues with Darwinian evolution (herbicide resistance – aka. “Superweeds”) are widespread and of great economic importance • The “causes” of herbicide resistance are more of a socioeconomic rather than agronomic issue • Weeds threaten global food security and society just as they have always done

  19. Questions?

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