Balancing steel and herbicides to reduce resistance – why resistance?
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Balancing steel and herbicides to reduce resistance – why
resistance?
Micheal D. K. OwenIowa State UniversityAmes, IA 50011 [email protected]
www.weeds.iastate.edu
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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
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Superweeds? Evolution does not
workthat way!
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Major weed shifts in Iowa
1950’s 2,4-D
1960’s Treflan, Prowl(trifluralin, pendimethalin)
70-80’s Lasso, Dual(alachlor, metolachlor)
80’-90’s Pursuit, Classic, etc.(imazethapyr, chlorimuron)
2000’s Roundup(glyphosate)
??? ?
??
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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
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Evolution of glyphosate-resistant weeds*19
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*www.weedscience.com
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Glyphosate-resistant weeds found in Iowa
Common waterhemp
Horseweed
Giant ragweed
Marestail
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Ohio Weed Gothic(a study in giant ragweed)*
*with apology to Grant Wood
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Evolution of herbicide resistance in common waterhemp
State where first reported*
Year Site of action
Iowa and Illinois 1993 ALS inhibitorsMissouri 1994 PS II inhibitorsIllinois 1996 ALS and PSII inhibitorsKansas 2001 ALS and PPO inhibitorsIllinois 2002 ALS, PS II and PPO inhibitorsMissouri 2005 ALS and PPO inhibitors and
glycinesIowa and Illinois 2009 ALS, PS II and HPPD inhibitorsNebraska 2009 Synthetic auxinsIowa 2011 ALS and HPPD inhibitors and
glycines
*www.weedscience.com
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Soybean in a common waterhemp field
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“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)
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Original population – year 1
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99% Control - Population still appears like the “original”
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Year 4 with the same weed managementprogram
Year 2+ - Adapted biotype quickly becomes the dominant weed
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Poor control – the weed population shiftis obvious and a serious problem
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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
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Integrated Weed Management
Mecha
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Cultural
HerbicidesHerbicides
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Cultural
Current Future
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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
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Questions?