Download “Noxious Weed Management Herbicides and Their Mechanism of

“Herbicides”
Mode of Action
Reeves Petroff
Pesticide Education Specialist et al.
MSU Extension
Classification of Herbicides

Application Method

Foliar Applied
• Plant contact

Soil Applied
• Soil contact

Broadcast
• Entire area

Spot
• Specified area
Classification of Herbicides

Application Timing

Preemergence
• Prior to seed
germination
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Postemergence
• After seed
germination and
active growth

Post-directed
• Directed to
particular portion of
plant once emerged
and growing
Classification of Herbicides

Plant/Soil
Environment

Selectivity
• Selective vs
nonselective

Systemic
• Mobile vs nonmobile in the plant

Residual Activity
• Extended vs nonextended soil
activity
Classification of Herbicides

Mechanism of
Activity

Mode of action (MOA)
How it kills
Herbicide Modes of Action

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1.
2.
3.
4.
5.
6.
7.
8.
Plant Growth Regulation
Photosynthesis Inhibitors
Photosynthetic Pigment Inhibitors
Plant Growth Inhibitors
Amino Acid Synthesis Inhibition
Lipid Biosynthesis Inhibition
Cell Membrane Disruption
Unclassified Activity
Types of Herbicide Injury
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1.
2.
3.
4.
5.
6.
7.
8.
Plant Growth Regulation
Photosynthesis Inhibitors
Photosynthetic Pigment Inhibitors
Plant Growth Inhibitors
Amino Acid Synthesis Inhibition
Lipid Biosynthesis Inhibition
Cell Membrane Disruption
Unclassified Activity
Mechanism of Action &
Herbicides Used

Plant Growth
Regulating
Herbicides
Plant Growth Regulation
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Mimics natural plant hormone –
Auxins.
Results in an imbalance of this growth
regulating hormone.
Cells of the leaf vein rapidly divide while
cells between the veins do not.
Cell division and respiration increase,
while photosynthesis does not.
Common Leaf Symptoms from PGR
Exposure
normal
cupped and blistered from
PGR exposure
Foliar PGR Application
short internode
accumulation
In new growth
Root Absorption of
Plant Growth Regulator Herbicides
translocation to
growing point
swollen
hypocotyl
callus formation on roots
lack of root
development
Plant Growth Regulation

Examples include:
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2,4-D
Dicamba
Picloram
Clopyralid
Triclopyr
Mechanism of Action &
Herbicides Used

Amino Acid
Synthesis
Inhibiting
Herbicides
Amino Acid Synthesis
Inhibition
Amino Acids = life!!
 Specific to plant AAs only
 Visual results are the result of
secondary injury

the injury as the beginning of a chain of
events that take place in the plant.
 symptoms take time to develop – it is
not an immediate process.

Amino Acid Synthesis
Inhibition
Amino Acid Synthesis
Inhibition

What are you going to see visually?
Initially there will be a general
yellowing of the treated plants.
 After 5 to 10 days, chlorosis results in
necrosis.

Plateau or Escort Injury Symptoms
Stunting
Chlorosis of
youngest tissue
Glyphosate (Roundup) Drift
chlorosis
stem proliferation
shortened
internodes
Amino Acid Synthesis
Inhibition
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Imidazolinones
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Arsenal
Plateau
Sahara
Top Site
Glyphosate
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Roundup
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Sulfonylureas
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Escort
Oust
Telar
Summary Ideas

Know symptoms
associated with
the different
classes of
herbicides

Can more easily
understand what
to expect?.
Summary

Just Remember:

“Worrying has killed more
people than work
because more people
worry than work.”