Download Mode-of-Action

Turfgrass Herbicide
Mode-of-Action
Tim R. Murphy
The University of Georgia
Herbicide Mode-of Action
Mode-of-Action - The entire sequence of
events that happen from the time the
herbicide is absorbed to the eventual plant
response (usually death).
Mode of Action
Three phases
* Absorption
* Movement to target site
* Inhibit biochemical reaction
Herbicide Mode-of-Action
The way a herbicide kills or inhibits the
growth of susceptible plants!!
Why understand herbicide MOA?
Better understanding of how herbicides
perform.
Diagnosing herbicide injury.
Professionalism.
Public relations.
Herbicide Classification
Selectivity
Herbicide movement in plants
Timing of application
Chemical Family
Mode of Action
Herbicide Classification - Selectivity
Selective
controls or suppresses one species of plant
without seriously affecting the growth of another
plant species.
Example
2,4-D will control many broadleaf weeds without
seriously affecting turfgrasses.
Herbicide Classification - Selectivity
Nonselective
Nonselective herbicides control plants
regardless of species.
Examples
Roundup Pro, Finale, Reward, Scythe
Contact
herbicides do
not move in
the plant
Phloem mobile herbicides move
up and down in the plant
Xylem mobile
herbicides move up
in the plant
Translocated herbicides move.
Herbicide Movement in Plants
Contact
 Rupture cell
membranes.
 Symptoms
appear within
hours.
 Need complete
coverage for
kill.
Xylem Mobile
Phloem Mobile
Taken up by
primarily by
roots.
Found in older
leaves that are
exporting sugars.
Move to points of
active growth or
food storage.
Affect shoot tips,
young buds and
leaves.
Can cause contact
burn.
Do not move
downward when
foliar applied.
Plant leaf cuticle.
Plant Processes Affected by
Turfgrass Herbicides
 Photosynthesis
 Amino acid and protein synthesis
 Cell division
 Cell membranes
 Pigment synthesis (none registered in turf)
 Growth regulation
 Growth inhibition
 Fatty acid synthesis
Photosynthesis
CO2 + H2O + Sunlight = C6H12O6
OR
Carbon dioxide + water + sunlight
will yield
Sugar
Triazines
Atrazine – Aatrex, Simazine - Princep
Metribuzin – Sencor
Used only on warm-season turfgrasses
Root and shoot absorbed (except simazine)
Inhibits photosynthesis, eventual membrane
disruption, requires light
Pre and Post control
Photosynthetic inhibitors
Atrazine, simazine, Sencor
 Light and active
photosynthesis
needed for activity
 These herbicides
interrupt energy flow
resulting in free
radicals
 Free radicals react
with cell membranes
Atrazine on bentgrass
Bentazon
Basagran T/O
All warm- and cool-season turfgrasses
contact, foliage absorbed
limited translocation
can move in xylem if root absorbed
inhibits photosynthetic electron transport
Bladex
Injury SymptomsPhotosynthesis Inhibitors
Source: W. K. Vencill, UGA
Cotoran
Oxadiazon
Ronstar
all turfgrasses, except centipede
readily shoot absorbed, less so by roots
can be foliage absorbed, “contact burn”
does not significantly translocate
MOA is related to photosynthesis, light required
inhibits key enzyme in chlorophyll synthesis,
toxic radicals formed, disrupts cell membranes
Amino acids
Building blocks of plant proteins
Enzymes mediate biochemical
reactions
Storage roles - seed reserves
Structural roles
Imidazolinones
Image, Plateau
warm-season grasses, except bahiagrass
rapid shoot and root absorption
translocates to meristematic areas
inhibits leucine, isoleucine and valine synthesis
growth is impaired and plants die over 1 to 3 wk
period
Image on bermuda
Sulfonylureas
Manor, Corsair, Manage,TranXit, Monument,
Revolver
rapid shoot and root absorption
translocates to meristematic areas
inhibits leucine, isoleucine and valine synthesis
growth is impaired and plants die over 1 to 3 wk
period
Sulfonylureas
 Manor, Blade – warm-season grasses, except
bahiagrass; also on Ky. Bluegrass
 Corsair – Ky. Bluegrass, bahiagrass,
bermudagrass
 Manage – all warm- and cool-season turfgrasses
 Revolver – bermuda, ‘Meyer’ zoysia
 Monument – bermuda, zoysia
 TranXit – bermuda, zoysia, centipede, overseeded
bermudagrass
Glyphosate
 Isopropylamine salt - Roundup Pro , GlyphoMate 41,
Razor Pro, Prosecutor
 Ammonium salt - Roundup ProDry
 Diammonium salt - TouchDown Pro
 foliage absorbed
 extensively translocated in phloem
 inhibits tryptophan, tyrosine and phenylalanine synthesis
 growth is impaired and plants die over 1 to 3 wk period
Cell Division
Plant growth is due to cell division and cell
elongation.
Dinitroanilines
 Benefin - Balan
 Oryzalin - Surflan
 Pendimethalin - Pendulum
 Prodiamine - Barricade
 Trifluralin - Treflan
 Shoot and root absorbed, no translocation
 Inhibit cell division (tubulin formation)
 Used on most warm- and cool-season turfgrasses
Dithiopyr
Dimension
MOA is similar to dinitroanilines
Shoot and root absorbed, no translocation
Inhibit cell division (tubulin formation)
Has POST activity on seedling crabgrass
Used on most warm- and cool-season
turfgrasses
DNA Root inhibition
pendimethalin on
zoysiagrass
Surflan on St.
Augustinegrass
Swollen, club shaped roots
Dimension on
bermudagrass
Cell Membranes
Contain the cellular contents and regulate
the entry and exit of substances that
promote or inhibit plant metabolism
Diquat
 Reward LS
 contact, very rapidly absorbed,does not translocate
 requires light for activity
 disrupts electron flow in photosynthesis
 leads to formation of free radicals which damages cell
membranes
 cellular fluids leak, followed by death
 used on dormant bermudagrass
Glufosinate
 Finale
 readily absorbed by leaves
 primarily contact activity, limited translocation
 inhibits key enzyme involved in conversion of ammonia
into amino acids
 toxic levels of ammonia build up, causes cell membrane
disruption, interferes with photosynthesis
 used on dormant bermudagrass
Carfentrazone
 Sold with phenoxy herbicides and dicamba as
PowerZone and SpeedZone
 Limited translocation
 Inhibits key enzyme in chlorophyll synthesis
 Causes buildup of phytotoxic compounds which
damages cell membranes
 Cellular fluids leak, followed by cell death
 All turfgrasses
Cell Membrane Disrupters
Finale, Reward, Paraquat
Finale on
zoysia
 Damage occurs within hours.
 Membrane destruction.
 No redistribution
 Complete coverage for kill.
Growth Regulator Herbicides
These herbicides affect several plant processes
such as cell division, cell enlargement, protein
synthesis and respiration. They act by upsetting
the normal hormonal balance in plants.
Growth Regulator Herbicides
 Phenoxys
 2,4-D, dichlorprop
 mecoprop, MCPA
 Benzoics
 Banvel, Vanquish
 Picolinic Acids
 Confront
 Turflon
 Lontrel
 SpotLight
 Quinolinecarboxylic
 Drive
Trimec on bermuda
Phenoxy, Benzoic Acid, Picolinic Acid
readily absorbed by foliage, less so by roots
extensively translocated
interfere with DNA, RNA and protein
synthesis
results in uncontrolled cell division and
elongation
vascular tissues are plugged, 1 to 3 wks
Phenoxy, Benzoic Acid, Picolinic Acid
Phenoxies – used on cool- and warm
season turfgrasses, except St. Augustine
Benzoic acids - used on cool- and warm
season turfgrasses
Lontrel – all cool- and warm-season grasses
Confront – cool- and warm-season grasses,
except St. Augustine
Turflon – Ky. Bluegrass and tall fescue
2,4-D Injury on Soybean
Growth Inhibition
Exact MOA not known
Inhibit root and shoot growth
Disrupt cell division, cell enlargement
Also may disrupt lipid synthesis, nucleic acid
and protein synthesis
Growth Inhibitors
Bensulide - Betasan, Pre-San
root absorbed, essentially no translocation
disrupts cell division and enlargement
Metolachor - Pennant
mainly shoot absorbed, some root uptake
translocates in xylem
inhibit root and shoot growth
disrupts protein, fatty acid and lipid synthesis
Fatty Acid Synthesis
Fatty acids are important components of cell
membranes
Inhibition fatty acid synthesis blocks
production of lipids needed for new cell
growth.
Fatty Acid Inhibitors
Cyclohexanediones
sethoxydim - Vantage, Poast
used only on centipedegrass and fine fescue
clethodim – Envoy
used only on centipedegrass
Rapidly absorbed by leaves, extensively
translocated via phloem to meristems
Inhibit key enzyme in fatty acid synthesis
Fatty Acid Inhibitors
Aryl-oxy-phenoxies
fenoxaprop - Acclaim Extra
fluazifop - Fusliade II
diclofop - Illoxan
Rapidly absorbed by leaves, extensively
translocated via phloem to meristems,
(diclofop translocation is slow)
Inhibit key enzyme in fatty acid synthesis
Fatty Acid Inhibitors
Aryl-oxy-phenoxies
fenoxaprop - Acclaim Extra
used on cool-season grasses and zoysiagrass
fluazifop - Fusilade II
Used only on tall fescue and bermudagrass
diclofop – Illoxan
Used only on bermudagrass
Fatty Acid Synthesis Inhibitors - Grass Herbicides
 Reddening of leaf
tissue.
 Discoloration of tissue
at and above the
nodes.
 Tissue and leaves in
the leaf whorl can
easily be separated
from the rest of the
plant.
 No broadleaf activity.
Fusilade on dallisgrass
Fatty Acid Synthesis Inhibitors
 Initial injury in meristematic regions occurs where
newest leaves are developing
 These regions will turn chlorotic, which is
followed by necrosis
 The affected area will become “rotted” and will
easily separate from rest of plant
 Injury will develop slowly (7 to 14 days)
“rotted” meristem
Non-Classified Herbicides
Organic Arsenicals
MSMA, DSMA, CMA, CAMA
foliage absorbed
extensive movement in xylem and phloem
interfere with ATP production
also interfere with enzyme activity and cell
division
Used on cool-season grasses, bermuda and
zoysiagrass
 Leaf burn on
broadleaves and
grasses with yellow leaf
tips on grasses
 Terminal yellowing of
grasses
MSMA on zoysia
Turf
Weed
Management
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