AGR 3102 (1) Principles of Weed Science Herbicide

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AGR 3102 (1)Principles of Weed
ScienceHerbicide

• Muhammad Saiful Ahmad Hamdani

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Week 8 Topics Covered

• Herbicides
• Classification cont
• Formulation

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• Herbicides Classification
• Selectivity selective vs. non-selective ?
• Activity contact vs. systemic ?
• Residual activity residual vs. non residual ?
• Time/type of application pre-plant,
  pre-emergence, post-emergence ?
• Placement soil, foliar/plant ?
• Methods of application banding, broadcast,
  directed, spot treatment, wiping ?

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Herbicides Classification cont

• G. Mode-of-Action
• Common method of grouping herbicides
  mode-of-action (MOA).
• Classification based on similarity/dissimilarity
  of the herbicides chemistry and action.
• Each MOA has a designated numerical system (WSSA)
  and alphabetical system (HRAC).

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What is MOA?????

• The first plant enzyme or site-of-action
  targeted/inhibited by the herbicide.
• Each herbicide group specifically inhibits
  specific functions, processes and systems in the
  cells.
• Different MOA group exhibits different injury
  symptoms.

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Commercial Products (Roundup)
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• 2 types of herbicides
• Inorganic compounds - old school
• - Copper sulphate, ammonium sulphate,
• ammonium sulphamate, ammonium nitrate
• ammonium thiocyanate
• - MOA as desiccant/desiccating agent
• - High enviromentally persistent in soil
  highly toxic to other organisms
• - Widely used in 1900s for aquatic and woody
• terrestrial plants, but no longer applicable.
• WHY?????

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• Organic compounds
• extensively synthesized following 2,4-D
• other PGR commercialization.
• widely used in agric and non-agric areas.
• differ from one to another by their MOA.
• In general, divided into several important MOA
  groups

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Classification by Mode of Action

1. Synthetic Auxins Auxin Transport Inhibitors
2. Amino Acid Biosysthesis Inhibitors
3. Fatty Acids Biosynthesis Inhibitors
4. Seedling Growth Inhibitors
5. Photosynthesis Inhibitors
6. Cell Membrane Disrupters
7. Pigment Inhibitors
8. Nitrogen Metabolism Disrupter
9. Unknown mode-of-action

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1. Synthetic Auxins Auxin Transport Inhibitors

• First commercialized in the 1940s to primarily
  control dicot weeds in many cereal crops.
• Broadleaf selective, systemic, post-emergence.
  Can affect monocots at high rates. Absorbed via
  foliar and roots.
• Short soil residual average 5 - 14 days.
• Synthetic auxin herbicides.

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• MOA cause an auxin overdose.
• Auxin or indol-3-yl-acetic acid (IAA)
  endogenous PGR crucial in cell division,
  differentiation, elongation.
• Induces ethylene and ABA (plant maturity and
  senescence).
• Overdose rapid uncontrolled cell development
  sudden plant maturing.
• Auxin transport inhibitors unbalance auxin
  unbalance cell development unbalance growth.

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2. Amino Acids Biosynthesis (ALS and EPSPS
enzymes) Inhibitors

• 2 major MOAs Acetolactate synthase (ALS)
  inhibitors and 5-Enolpyruvylshikimate 3-phosphate
  synthase (EPSPS) inhibitors.
• ALS synthesize 3 amino acids (leucine,
  isoleucine, valine) EPSPS (acids phenylalanine,
  tyrosine and tryptophan) building block for
  protein. Protein needed for production of new
  cells metabolic activity.
• Both systemic.
• ALS pre- and post-emergence, EPSPS post.
• ALS and EPSPS inhibitors non-selective.

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• Inhibition of ALS EPSPS shutdown of metabolic
  activity no cell produced.
• ALS herbicides and glyphosate considered among
  the safest herbicides because ALS
  shikimate-pathway exist only in photosynthetic
  plants microorganisms and not in humans
  animals.
• Soil residual varies among ALS herbicides,
  generally about 2 weeks 3 years (long
  persistence). EPSPS- little-no soil activity,
  residue 2-200 days.

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3. Fatty Acids Biosynthesis (ACCase enzyme)
Inhibitors

• Selective-commonly referred to as graminicides
  (grass killers). Post-emergence, systemic.
• Inhibit fatty acid synthesis in plant plastid.
• Fatty acids important for development of meristem
  tissues.
• Some are sold as esters (ethyl or methyl, buthyl)
  to increase absorption.
• Grass ACCase in plastid highly sensitive to
  ACCase herbicides, others not

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FOPs
DIMs
DEN
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4a. Seedling Growth Inhibitors (Root Shoot)

• 2 MOAs microtubule inhibitors and cell wall
  (cellulose) biosynthesis inhibitors.
• Inhibit root and shoot development by interfering
  with cell division in meristematic areas.
• Effective only on germinating, small-seeded
  annual grasses and some broadleaves (seedling
  selective, systemic, pre-emergence).

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• Some need incorporation into the soil (esp.
  dinitroanilines) - subject to photo-degradation
• Have relatively long residual activity (more than
  a year).

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4b. Seedling Growth Inhibitors (Shoot)

• 2 MOAs lipid synthesis inhibitors cell
  division inhibitors (VLCFA synthesis). Applied as
  pre-emergence/planting.
• Cause abnormal cell development or prevent cell
  division in germinating seedlings.
• Seedling-selective systemic. Most effective on
  annual grasses and sedges, some can control
  small-seeded annual broadleaves.

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• Lipid synthesis inhibitors need soil
  incorporation, absorbed by emerging shoots.
• Cell division inhibitors absorbed by emerging
  shoots and roots.
• No control of established weeds.

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5. Photosynthesis (at PS II) Inhibitors

• 2 types soil applied herbicides (pre-
  post-emergence) and foliar applied herbicides
  (post-emergence). Both systemic.
• Broadleaf selective.
• MOA block the photosynthesis process no food
  produced.

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6. Cell Membrane Disrupters

• 2 MOAs Protoporphyrinogen oxidase (PPO)
  inhibitors and PS I inhibitors. Both
  post-emergence and non-systemic (contact
  herbicides).
• PPO inhibitors and PS I inhibitors provide
  broad-spectrum control of many different species.
• PS I herbicide Paraquat extremely toxic, no
  antidote so far. 5-10 ml fatal to human.

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• They burn plant tissues or desiccation. Symptom
  within an hour esp for Paraquat.
• Phytotoxicity increased by sunlight.
• PS I inhibitors have no phytotoxicity in soil (no
  root uptake).

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7. Pigment Inhibitors (Bleaching Agents)

• 2 MOAs Carotenoids synthesis inhibitors HPPD
  (4-hydroxyphenyl-pyruvate-dioxygenase)
  inhibitors.
• Provide control of many annual broadleaves and
  some grasses (non-selective, systemic, some pre-,
  some post-emergence, some both).
• Carotenoids synthesis inhibitors inhibit
  carotenoids (chlorophyll protector) biosynthesis.

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• HPPD inhibitors interfere with normal
  chlorophyll activity.
• Carotenoid or chlorophyll inhibited sun
  radiation damages chlorophyll pigments and the
  plant becomes bleached and dies.
• Referred to as bleachers.

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8. Nitrogen Metabolism Disrupter

• Glufosinate-ammonium. Non-selective. Group H
  (HRAC) 10 (WSSA).
• MOA disrupting nitrogen metabolism, important
  for amino acids synthesis.
• Have both contact (major) and systemic (minor)
  actions on plants.
• Phytotoxicity increased by sunlight.
• Little to no soil activity (rapidly degraded by
  microorganisms).

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9. Unknown MOA Herbicides

• Unknown MOA. Basically contact but some have
  limited translocation.
• Non-selective, post-emergence.
• Some have no soil activity and tightly bound to
  soil, some unknown.
• Some used as soil fumigants. Kill everything in
  the soil.

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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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Herbicides Formulation

• Active ingredient (a.i.) chemical that causes
  phytotoxicity controls the target weed the
  herbicide.
• Rarely for herbicide products to be made up only
  of a.i.
• Often diluted in other chemicals.
• Other chemicals additives, diluents, extenders
  or adjuvant (no herbicidal activity) inert
  ingredients.

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• Purpose make the product easier to mix apply,
  increase its efficacy, improve formulation
  stability improve shelf-life/longevity.
• Mixture of a.i. and inert ingredients
  formulation.
• Herbicides are sold in various formulations,
  depending upon
• (1) the solubility of the active ingredient in
  water
• (2) the manner in which the product is applied
  (i.e.
• dispersed in water or applied in the dry
  form).
• 2 TYPES OF HERBICIDE FORMULATION

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A) Dry Formulations

• 1. Granules (G)
• A dry formulation (a.i., coated or adhered to
  some type of inert granule). Applied just as they
  are purchased with no mixing. Special granular
  spreader is required.

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• 2. Pellets (P)
• A dry formulation - similar to granules only
  much larger. Pellets are applied directly to the
  target area by hand or with special spreaders.

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• 3. Wettable Powder (W or WP)
• A dry powder (a.i., a diluent, and surfactants),
  water soluble. Spray tank agitation is necessary
  to avoid settling.
• 4. Soluble Powder (SP)
• A dry formulation that contains a high percent
  (gt50) a.i, water soluble. Need initial agitation
  to dissolve. No after-dissolve agitation is
  needed.

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• 5. Water-Dispersible Granules (WDG) Dry
  Flowable (DF)
• A dry formulation, water soluble. Easier to
  handle and measure than wettable powders. Spray
  tank agitation is necessary to avoid settling.

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B) Liquid Formulations

• 1. Water Soluble Concentrate/Solution (WSC/S)
• A liquid formulation (a.i., water, sometimes a
  surfactant), water soluble/carrier.
• Have an amine (ammonium salt) or mineral salt in
  the molecule that enables water solubility.
• Agitation is not necessary.

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• 2. Emulsifiable concentrate (E or EC)
• A concentrated liquid (a.i., petroleum solvents,
  emulsifier), oil and water based/soluble.
  Emulsifier - allows the formulation to be mixed
  with water to form an emulsion.
• Upon mixing with water, they take on a "milky"
  appearance. Mild agitation is sufficient.

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• Oil Soluble (OS)
• A liquid formulation (a.i. dissolved in oil or
  some other organic solvent. Must be applied in an
  oil-based carrier such as diesel fuel or
  kerosene. Mild agitation is sufficient.

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• Liquid/Flowable (F or L)
• A thick slurry-like liquid (a.i., water, and
  stabilizers), water soluble. Spray tank agitation
  is necessary to avoid settling.

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• 5. Ready-to-Use Low Concentration Solutions
  (RTU).
• Ready to use and require no further dilution
  before application.
• Consist of a small amount of active ingredient
  (often 1 or less per unit volume) dissolved in
  an organic solvent.

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1. Dry formulations Spreader (Rotary, Drop)
2. Liquid formulations Sprayer (Handheld, Knapsack,
   Boom)

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• Drop

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Sprayers
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Some Things to Remember.

• Photosynthesis food
• Pigments (energy/light capture) food
• Amino acids proteins metabolism (growth)
• Cell membranes (lipids) cell shape rigidity
• Cell division growth
• Hormone growth and development
• Fatty acids meristematic tissues development
• Nitrogen metabolism amino acids synthesis

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Some Things to Remember.

• Herbicide formulations herbicide mixtures and
  forms.
• Different formulation needs different carrier and
  applied differently.