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My role:
- Overview of herbicide resistance
- MOA of auxins
- Resistance to auxin herbicides
Auxin Herbicides and Weed Resistance Management Reid J. Smeda, - - PowerPoint PPT Presentation
Auxin Herbicides and Weed Resistance Management Reid J. Smeda, - - PowerPoint PPT Presentation
Auxin Herbicides and Weed Resistance Management Reid J. Smeda, University of Missouri My role: Overview of herbicide resistance MOA of auxins Resistance to auxin herbicides Remember the theme saying of this past movie? The
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Remember the theme saying of this past movie?
The Highlander
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Soybean field adjacent to I-55 in southern Missouri
It only takes one!
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4 Synthetic auxins
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Facts about resistance:
- 252 total species (146 dicots, 106 monocots)
- 23 of 26 different herbicide modes of action have
resistant weeds (163 different herbicides)
- 92 crops with reported resistant weeds in 69
different countries
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Nature’s response
Crockett County, TN, 2002 Photo -Chism Craig
Marestail Weeds that used to die no longer all do
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Auxins:
- Four major classes
- Phenoxyalkanoic acids (2,4-D)
- Benzoic acid (dicamba)
- Pyridines (picloram)
- Quinoline carboxylics (quinclorac)
- Older chemistries
- 2,4-D developed in 1940’s
- Dicamba registered in 1967
- Widely used in:
- Grass crops (corn, sorghum, cereal grains (wheat)
- Turfgrass (industrial, pastures, home lawns)
- Burndown ahead of crop planting or in fallow areas
- Industrial Vegetation Management (IVM)
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Why develop crops resistant to auxin herbicides?
- Technological advances
- Need; evolution of highly problematic species
with multi-MOA resistance (pigweeds, ragweeds, horseweed, kochia)
- Systemic, broad-spectrum, highly active
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How do auxin herbicides work?
IAA (auxin) Dicamba 2,4-D
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Roles of auxin:
- Phototropism
- Gravitropism
- Apical dominance
- Fruit development
- Abscission
- Root development
- Concentrated in meristematic tissue
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How much auxin induces effects?
- As a rooting hormone, auxin initiates
effects at 10 ppm
- Dicamba applied to broadleaf weeds in
soybeans results in 3,995 ppm at the 0.5 lbs ae/A rate.
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Physiological response:
Auxin herbicides enter the plant cell by imitating natural auxins
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Initial response includes leaf and stem movement (24 hours)
Dramatic increase in ethylene contributes to visual symptoms
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Binding to ARP will initiate a signal transduction pathway that leads to many concurrent events
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Dayan et al., Weed Sci. 2010
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Net result is collapse of plant tissue
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Could auxin-tolerant crops lead to selection for resistance?
University of Nebraska
Lethal dose
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What can we learn about glyphosate resistance to avoid repeating history with auxins?
- Resistance was never the intent when we
developed herbicides
- Never say never (no silver bullets)
- Rapid adoption of technology (>90% acres)
- Effective control does not mean abandon
- ther techniques or herbicide MOA’s
- Use the right rate at the right time
- (Effectiveness) x (acres treated) x
(dependence) = risk
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Selection matrix for people to be around the president during World War I:
- Dr. Mark Lonsdale, CSIRO