herbicide mode of action
DESCRIPTION
Herbicide Mode of Action. Fabián D. Menalled Cropland Weed Specialist Dept. Land Resources and Environmental Sciences Montana State University [email protected]. Why Understand Herbicide Mode of Action?. Better understanding of how herbicides perform Improve herbicides performance - PowerPoint PPT PresentationTRANSCRIPT
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Herbicide Mode of Action
Fabián D. Menalled
Cropland Weed SpecialistDept. Land Resources and Environmental
SciencesMontana State University
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Why Understand Herbicide Mode of Action?
• Better understanding of how herbicides perform
• Improve herbicides performance
• Diagnosing herbicide injury
• Prevent and manage herbicide resistance
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Some Things to Remember….
• Photosynthesis (food)
• Pigments (energy/light capture)
• Respiration (energy)
• Amino acids (proteins/growth)
• Lipids (cell membranes)
• Mitosis (cell division)
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Why do we use herbicides?
• Use herbicides to achieve your goal – Reduce the impact of invasive species
– Secure the presence of targeted speciesBut not all herbicides are
equal!
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Herbicide Classification - Selectivity -
• Selective: controls or suppresses one
species of plant without seriously affecting
the growth of another plant species
– 2,4-D
• Nonselective: control plants regardless of
species
– Roundup
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Site of Absorption and Translocation
Foliar Contact
(Gramoxone)
Root Contact
(Treflan)
Phloem
(Roundup)
Xylem
(Spike)
Xylem and Phloem
(Banvel, Tordon)
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Commercial Products (Roundup, Durango)
Mode of Action (Amino Acid Biosynthesis Inhibitors)
Site of Action (EPSPS inhibitor)
Chemical Family (Glyicines)
Active Ingredient (Glyphosate)
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Mode of Action •Sequence of events from
absorption of the herbicide into the plant until the plant dies
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Contact
AbsorptionMovement
Site of Action
Herbicide Mode of Action
Toxicity
CO2 + H2O Sugar + O2
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Classification by Mode of Action
1) Plant Growth Regulators2) Amino Acid Biosysthesis Inhibitors3) Lipid Biosynthesis Inhibitors4) Cell Division Inhibitors5) Photosynthesis Inhibitors6) Cell Membrane Disrupters7) Pigment Inhibitors8) Unknown mode of action
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Plant Growth Regulators
• Synthetic auxins (regulate plant growth)
• Affect several plant processes such as cell division, cell enlargement, protein synthesis and respiration
• Act by upsetting the normal hormonal balance in plants
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Plant Growth Regulators
• Herbicide uptake is primarily through the foliage but root uptake is possible
• Translocate in both xylem and phloem
• Effective on perennial and annual broadleaf weeds
• Selectively kill broadleaf plants
• Injury may occur in grasses
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Chemical Family
Common Name Trade Name
Phenoxy acetic acids 2,4-D 2,4-D, Campaign,
Crossbow,
Landmaster BW,
others
2,4-DB Butyrac
MCPA MCPA, others
Benzoic acid dicamba Banvel, Clarity
pyridines clopyralid Curtail, Transline
fluroxypyr Starane
picloram Tordon
Examples of PGR
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More examples of PGR
• Transline & Curtail: Clopyralid
• Milestone: Amynopiralid
• Weedmaster: 2,4-D + Dicamba
• Grazon P&D: Triclopyr + Picloran
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PGR Symptoms• Most obvious on newly developing leaves
• Abnormal growth resulting in twisting stems
• Stems swelling due to rapid cell division
• Leaves on broadleaf plants exhibit cupping, crinkling, strapping, or drawstring affect
• Symptoms on grass plants include leaf rolling, crinkling, brace root fusion and malformation.
• Flower sterility and missing grain in crops
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Parallel veination due to 2,4-D
Photo: HMOA and Crop Injury Symptoms.
Univ. of Minnesota Extension
PGR Symptoms
•
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Leaf cupping caused by dicamba
Photo: HMOA and Crop Injury Symptoms.
Univ. of Minnesota Extension
PGR Symptoms
•
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Puckered soybeans from Tordon
Photo: Kansas State University Extension
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Tordon runoff into soybean fieldTordon runoff into soybean field
Photo: Kansas State University Extension
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Growth Regulator Use Concerns
• Herbicide resistance
• Drift and injury to nontarget plants
• Carryover: Tordon
• Groundwater Contamination:
Tordon
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Questions, so far?
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Amino Acid Synthesis Inhibitors
• Prevent synthesis of certain amino acids produced
by plants but not animals
• Excellent foliar and root absorption
• Broad weed spectrum
• Translocates to shoot and root new growth in both
xylem and phloem
• Plants stop growing shortly after application
• Plant death may be slow (10 days+)
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Chemical Family Common Name Trade Name
Sulfonylureas chlorsulfuron Glean, Telar
thifensulfuron Harmony GT
nicosulfuron Accent
Imidazolinones imazamethabenz
Assert
imazapic Plateau
imazamox Raptor
Amino acid derivates glyphopste Roundup, Glyphomax, Rodeo, and others
Examples of Amino Acid Synthesis Inhibitors
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More Examples of Amino Acid Synthesis Inhibitors
• Amber: Triasulfuron• Cimarron, Escort: Metsulfuron• Journey: Imazapic + glyphosate:
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Chlorosis of New Growth on Tansy Mustard
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Plateau Injury Symptoms
Stunting
Chlorosis ofyoungest tissue
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EPSP Inhibitors(Glyphosate)
• Tightly adsorbed and inactive in soil
• Phloem translocated
• Inhibits EPSP enzyme responsible for production of aromatic amino acids phenylalinine, tyrosine and tryptophan
• Very nontoxic
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Gradual Death from Roundup Treatment
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Glyphosate (Roundup) Injuries
chlorosisshortened internodes
stem proliferation
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Roundup on AzaleaYellowing of new growth
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Strapped leaves on a maple due to glyphosate
Mimics 2,4-D and other hormone-like herbicides
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Questions, so far?
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Photosynthesis Inhibitors• Control annual or perennial grasses or broadleaves
• Shut down the photosynthetic process
• Slow starvation of the plant
• However, the plant experiences a more rapid death be due to the production of secondary toxic substances
• Injury symptoms: yellowing (chlorosis) of leaf tissue followed by death (necrosis) of the tissue
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Photosynthesis Inhibitors• Controls big sage, shinnery
and other oaks, tarbush and creosote bush
• Sagebrush thinning and brush sculpting programs
• Rangeland, pastures, clearings for wildlife and other non-cropland areas
tebuthiuron
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Photosynthesis Inhibitors• Injury symptoms:
– Only occur after the cotyledons and first leaves emerge
(do not prevent seedlings from germinating or
emerging)
– yellowing (chlorosis) of leaf tissue followed by death
(necrosis) of the tissue
– Older and larger leaves affected first: they take up
more of the herbicide-water solution as they are the
primary photosynthetic tissue of the plant
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Injury from PSII herbicideNote the interveinal chlorosis
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Cell Membrane Disruptor
• Postemergence contact herbicides
• Little soil activity
• Activated by exposure to sunlight to form oxygen compounds such as hydrogen peroxide
• These oxygen compounds destroy plant tissue by rupturing plant cell membranes
• Perennial weeds usually regrow because there is no herbicide movement to underground root or shoot systems
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Cell Membrane Disruptor
• Controls weeds in just 24 to
48 hours
• Broad-spectrum and non-
selective control of grasses,
broadleaf weeds and sedges
• Cheatgrass, kochia, Russian
thistle, annual mustards
• No residual effect
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Cell Membrane Disruptor, Injuries
Rapid browning (necrosis) of plant tissue
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Paraquat injury on corn leaves
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Why Understand Herbicide Mode of Action?
• Better understanding of how herbicides perform
• Improve herbicides performance
• Diagnosing herbicide injury
• Prevent and manage herbicide resistance
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Herbicide Resistance is NOT due to:
1. Sprayer skips or
plugged nozzles
2. Weather problems that
cause poor control
3. Plants that are ‘naturally tolerant’ to the
herbicide
4. Genetic changes caused by the herbicide
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Herbicide Resistance is:The ability of a plant to survive and
reproduce after treatment with a dose
of herbicide that would normally kill
the plantBanvel-
resistant kochia
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Where do Resistant Weeds Come From?
One in one million, billion, trillion….?
It’s all about selection…..
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Herbicide Resistance
• Selection intensity– Herbicide efficacy
• Length of soil residual period
– Number of herbicide applications / year
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Selection Pressure is Affected by:
Herbicide Quality
“Better” herbicide = more
chance of resistance
Is herbicide resistance a
problem in range and wildlands?
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Resources• University of Minnesota:
– Herbicide Mode of Action and Injury Symptoms (http://www.extension.umn.edu/distribution/cropsystems/DC3832.html)
• Kansas State University:
– Herbicide Mode of Action – (http://www.oznet.k-state.edu/library/crpsl2/c715.pdf)
• Montana State University:
– Preventing and Managing Herbicide-resistant Weeds in Montana (http://www.montana.edu/wwwpb/pubs/mt200506.html)
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Questions?