herbicide resistant weeds & crops: a north american perspective. tom mueller university of...
TRANSCRIPT
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Herbicide Resistant Weeds & Crops: A North American Perspective.
Tom Mueller
University of Tennessee
Knoxville, TN, USA
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Overview of presentation
• Herbicide resistant crops– How widespread?– Effect on weed control– Effect on development of herbicide
resistance
• Herbicide resistant weeds– Occurrence– Effect on farmers
• My Perspective….
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My perspective
• Herbicide tolerant crops can be an emotional issue
• If one wants to see a problem, one will see one
• If one does not want to see a problem, one will not see one
• As is often the case, we only see what we want to see…..
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Defining a few terms
• Herbicide Resistant Crop– Genetically Modified Organisms (GMOs)– Transgenic
• Herbicide Resistance = – Inherited ability of a weed population to
survive and reproduce after exposure to a herbicide dose (rate) that would control an unselected (sensitive) population
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Glyphosate Tolerant Crops
• RoundupReady (RR) varieties now common in USA– Soybean (>90%)– Cotton (70%)– Corn (~50%, still increasing)– Canola (not a US crop, but in Canada)
• Mainly Monsanto Ag Products
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Why do US farmers like RR?
• The System works!!– Kills many weeds, both small and large– Crop safety, can have overlaps– Safe to people spraying (glyphosate is not toxic)
• Monsanto owns seed companies….
• System is simple– One chemical… very easy
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Other types of HT crops
• LibertyLink Crops (Bayer)– Tolerant to glufosinate– Canola– Corn, soybeans
• Some very promising lines
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Some resistance to GMOs
• In practice, the United States has conducted a large-scale feeding trial
• ~300 million US citizens have consumed GMO crops for ~ 12 years.
• No negative dietary effects
• None…
• There is no toxicological reason not to allow GMO crops to be used.
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Herbicide Resistant Weeds
• Weeds have been adapting to herbicide use for many years
• Selection pressure allows for survivors to make seed and fill that open niche
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(Conyza canadensis)
(Amaranthus palmerii)
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Distribution of HR weeds
• More prevalent where glyphosate continually used
• Cotton/soybean farms
• Southeastern United States
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Two main weedy species
• Conyza canadensis– Winter annual
• Amaranthus palmerii– Summer annual
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Conyza canadensis
• Very widespread– Several million hectares infested
• Only a problem in no-tillage systems
• Farmers using additional chemicals– 2,4-D/dicamba + flumioxizan prior to planting
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(Conyza canadensis)
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Photo credit: Chism CraigPhoto credit: Chism Craig
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Conyza canadensisResistant to glyphosate in TN
• Wind-blown seed
• Need more herbicides
• Need more tillagePhoto courtesy ofChism Craig
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Amaranthus palmerii
• Dioecious summer annual
• Prolific seed producer
• Can grow 2.5 cm/day in summer
• Greatly reduces crop yield
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Cotton field 2004
0.8 kg ae/ha glyphosate 14 DAA
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West Tennessee 2008 4 kg/ha glyphosate in 1st spray
3 kg/ha glyphosate applied in 2nd application
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HR Weeds effect on Farmers
• Use more herbicides
• In extreme cases, hire people to hoe the fields
• Still using RR crop varieties
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Other areas
• Canada, upper midwest US
• Minimal glyphosate Resistance problems
• No GMO wheat
• GMO canola has several modes of action– 50% RR, 30% LL, 15% Imi, 5% non HT– Can rotate between alternate modes of action
• Other weeds have developed resistance– ACCase or ALS resistance
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Over the larger area
• “Most” farmers have no “major” weed resistance problems
• More farmers will have HR weeds in the next few years
• As RR corn use increases, will see more HR problems
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The most common problem
• RR corn “volunteers” in soybeans
• A RR crop (corn) becomes a weed in a different RR crop (soybeans)
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Do you see RR corn plants?
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Final thoughts
• HT crops widely used
• Few HR weeds, but more each year
• Once a farmer gets them, is a major problem
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One sees what one wants to see…..
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• CanadaQuestions??