Download Weed 3: Weed establishment

AGR 3102 (1)
Principles of Weed Science
Herbicide
Muhammad Saiful Ahmad Hamdani
Week 8 – Topics Covered
Herbicides:
Classification cont…
Formulation
Herbicides Classification…
•
•
•
•
Selectivity: selective vs. non-selective 
Activity: contact vs. systemic 
Residual activity: residual vs. non residual 
Time/type of application: pre-plant, preemergence, post-emergence 
• Placement: soil, foliar/plant 
• Methods of application: banding, broadcast,
directed, spot treatment, wiping 
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).
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.
Mode of Action
(EPSPS Inhibitors)
Site of Action (EPSPS-shikimate
pathway)
Chemical Family (Glycines)
Active Ingredient (Glyphosate)
Commercial Products (Roundup)
•
2 types of herbicides:
1.
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terrestrial plants, but no longer applicable.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?????
2. 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:
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
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.
• 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.
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.
• 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). EPSPSlittle-no soil activity, residue 2-200 days.
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
FOPs
DIMs
DEN
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).
• Some need incorporation into the soil (esp.
dinitroanilines) - subject to photodegradation
• Have relatively long residual activity (more
than a year).
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.
• Lipid synthesis inhibitors need soil
incorporation, absorbed by emerging shoots.
• Cell division inhibitors absorbed by emerging
shoots and roots.
• No control of established weeds.
5. Photosynthesis (at PS II) Inhibitors
• 2 types: soil applied herbicides (pre-& postemergence); and foliar applied herbicides
(post-emergence). Both systemic.
• Broadleaf selective.
• MOA: block the photosynthesis process = no
food produced.
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 broadspectrum control of many different species.
• PS I herbicide Paraquat: extremely toxic, no antidote
so far. 5-10 ml fatal to human.
• 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).
7. Pigment Inhibitors (Bleaching Agents)
• 2 MOAs: Carotenoids synthesis inhibitors & HPPD (4hydroxyphenyl-pyruvate-dioxygenase) inhibitors.
• Provide control of many annual broadleaves and some
grasses (non-selective, systemic, some pre-, some postemergence, some both).
• Carotenoids synthesis inhibitors inhibit carotenoids
(chlorophyll protector) biosynthesis.
• 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”.
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).
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.
Why Understand Herbicide
Mode of Action?
• Better understanding of how herbicides
perform
• Improve herbicides performance
• Diagnosing herbicide injury
• Prevent and manage herbicide resistance
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.
• 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:
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.
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.
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
(>50%) a.i, water soluble. Need initial agitation
to dissolve. No after-dissolve agitation is
needed.
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.
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.
•
•
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.
3.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.
4.
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.
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.
1.Dry formulations: Spreader
(Rotary, Drop)
2.Liquid formulations Sprayer
(Handheld, Knapsack, Boom)
Drop
Sprayers
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
Some Things to Remember….
• Herbicide formulations = herbicide
mixtures and forms.
• Different formulation needs
different carrier and applied
differently.