herbicide resistant weeds & crops: a north american perspective
DESCRIPTION
Herbicide Resistant Weeds & Crops: A North American Perspective. Tom Mueller University of Tennessee Knoxville, TN, USA. Overview of presentation. Herbicide resistant crops How widespread? Effect on weed control Effect on development of herbicide resistance Herbicide resistant weeds - PowerPoint PPT PresentationTRANSCRIPT
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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??