Herbicide Mode of Action
Categories
Table of Contents
- Introduction
- Herbicides Causing Injury to New Growth and
with the Potential to Move From Leaves to Roots
- Herbicides Causing Injury to Old Growth and With
the Potential to Move Only Upward
- Herbicides Applied to the Soil With the
Potential to Injure Emerging Seedlings
- Herbicides Causing Immediate Injury With Little
or no Movement
- Acknowledgements
Introduction
Herbicides are chemicals with complex chemical structures. While
each chemical has unique properties, a family of herbicides has
similar chemical structures with many similar characteristics. This
Factsheet explains:
- how chemicals are grouped into categories based on their mode
or site of action
- some of the plant injury symptoms of chemicals and
- the fate of these herbicides in the soil.
Herbicide half life in soil is given as a typical or average value
as listed in the Weed Science Society of America Herbicide Handbook.
These values vary depending on environmental conditions and soil
type.
Herbicides Causing Injury to New Growth and
With the Potential to Move From Leaves to Roots
Lipid Synthesis (ACCase) Inhibitors
Site of Action Group 1
Inhibitors of acetyl CoA carboxylase (ACCase) also known as "Grass
Growing Point Disintegrators"
Plant Injury Symptoms
- Aryloxyphenoxyproprionates (phloem mobile): Injury on grass
plants only. All are systemic but diclofop and fenoxaprop are
less mobile and do not control perennial grasses. Newer leaf tissue
will be yellow (chlorotic) or brown (necrotic) and the leaves
in the whorl be easily pulled out. Symptoms develop slowly. Prone
to resistance development.
- Cyclohexanediones (systemic): Same as for the aryloxyphenoxyproprionates.
Herbicide Breakdown
- Aryloxyphenoxyproprionates: Most herbicides in this category
are broken down by microbial action. Anaerobic conditions may
delay breakdown. Low mobility in soil. Little or no soil activity.
- Half life in soil:
- fenoxaprop - 9 days (aerobic conditions), 30 days (anaerobic)
- fluazifop - 15 days
- diclofop - 30 days at pH 7.0
- quizalofop - 60 days
- Cyclohexanediones: Most herbicides in this category are broken
down by microbial action. These herbicides are generally non-persistent
in soils.
- Half life in soil:
- clethodim - 3 days
- sethoxydim - 5 days
Table 1. ACCase Inhibitors
Aryloxyphenoxyproprionates (Group 1)2
"fops"
| Trade1
Names |
Common Names |
| HOEGRASS |
diclofop-methyl |
| ACCLAIM SUPER |
fenoxaprop-p-ethyl |
| EXCEL SUPER |
fenoxaprop-p-ethyl |
| FUSILADE II |
fluazifop-p-butyl |
| VENTURE |
fluazifop-p-butyl |
| ASSURE II |
quizalofop-p-ethyl |
Cyclohexanediones (Group 1) "dims"
| Trade1
Names |
Common Names |
| SELECT |
clethodim |
| POAST ULTRA |
sethoxydim |
| ACHIEVE |
tralkoxydim |
1 Herbicide Trade names are in capitals
and common names are in lower case in all tables.
2 The site of action group numbers are
shown in brackets (as established by the Weed Science Society of
America).
Amino Acid Synthesis Inhibitors; Branch Chain Amino
Acid Inhibitors
Site of Action Group 2
Inhibitors of acetolactase synthase (ALS) and also called acetohydroxyacid
synthase (AHAS)
Plant Injury Symptoms
- Imidazolinones (phloem mobile): Also referred to as "imi"
herbicides. Grass plants may be stunted with interveinal yellowing
(chlorosis) or purpling. Corn plants may be stunted and show root
pruning or stunting. Leaves emerging from the whorl may be yellow
to translucent in appearance. Broadleaf plants may be stunted
and chlorotic or purple. Leaves may be yellow in appearance and
leaf veination may appear red or purple in colour. Symptoms take
1-2 weeks to develop. Prone to resistance development.
- Sulfonylureas (phloem mobile): Same symptoms as for the imidazolinones.
- Sulfonanilides (phloem mobile): Sulfonanilides are also known
as Triazolopyrimidines or TPS. Same symptoms as for the imidazolinones.
Herbicide Breakdown
- Imidazolinones: These herbicides are broken down primarily by
microbes with very little degradation under anaerobic conditions.
They are strongly bound to soil organic matter. Dry conditions
cause them to be adsorbed to soil particles and wet conditions
cause the herbicide to be free for breakdown and plant uptake.
At soil pH progressively below 6.5 herbicide is more tightly bound
to the soil OM and is unavailable for breakdown. Warm moist soils
above pH 6.5 increase microbial breakdown. Soil mobility is low.
There is more carryover in low pH soil and this can create a recropping
problem for sensitive crops.
- Half life in soil:
- imazamox - 20-30 days,
- imazethapyr - 60-90 days,
- imazapyr - 25-142 days depending on conditions
- Sulfonylureas: Primarily broken down by hydrolysis and microbes.
SU herbicides are more tightly adsorbed to soil particles and
soil OM at low pH. SU herbicides carryover more in higher pH soils
since acid hydrolysis ceases at high pH levels. The rate of hydrolysis
is greatest at pH below 6.8 and as the temperature increases.
Variable pH across a field can greatly affect the ability of a
herbicide to persist in the soil. More carryover in high pH soil.
- Half life in soil:
- triflusulfuron - 2-4 days
- tribenuron - 10 days
- prosulfuron - 10 days
- thifensulfuron - 12 days
- ethametsulfuron - ? days
- foransulam - ? days
- nicosulfuron - 21 days
- triflusulfuron - 2-4 days
- primisulfuron - 30 days
- chlorsulfuron - 40 days
- chlorimuron - 40 days (more at high pH)
- Triazolopyrimidine Sulfonanilides (TPS): Primarily degraded
by microbes. Activity and degradation increases as the soil pH
increases. Degradation increases in soils with high pH because
in high pH soils the chemical is not adsorbed and are available
for plant uptake and microbial breakdown. All factors that increase
microbial activity also increase herbicide degradation. More carryover
in low pH soils. Recropping to sensitive species can be a problem
with some products.
- Half life in soil:
- cloransulam 8-10 days
- flumetsulam: 1-3 months, less at higher pH)
Table 2. ALS Inhibitors
Imidazolinones (Group 2)
| Trade Names |
Common Names |
| VIPER1 |
imazamox |
| MERIDAN2 |
imazamox |
| ARSENAL |
imazapyr |
| PURSUIT |
imazethapyr |
| PATRIOT2 |
imazethapyr |
| CLEANSWEEP2 |
imazethapyr |
| CONQUEST2 |
imazethapyr |
Sulfonylureas (Group s)
| Trade Names |
Common Names |
| CLASSIC |
chlorimuron |
| TELAR |
chlorsulfuron |
| MUSTER |
ethametsulfuron-methyl |
| ACCENT |
nicosulfuron |
| ULTIM |
nicosulfuron/rimsulfuron |
| BEACON |
primisulfuron |
| PEAK3 |
prosulfuron |
| ELIM |
rimsulfuron |
| PRISM |
rimsulfuron |
| PINNACLE |
thifensulfuron |
| REFINE EXTRA |
thifensulfuron-methyl/tribenuron-methyl |
| UPBEET |
triflusulfuron-methyl |
Sulfonanilides (Group 2)
| Trade Names |
Common Names |
| FIRST RATE** |
cloransulam** |
| BROADSTRIKE DUAL |
flumetsulam4 |
| BROADSTRIKE TREFLAN |
flumetsulam4 |
| FIELDSTAR |
flumetsulam4 |
| STRIKER |
flumetsulam4 |
| not determined |
foramsulam** |
** currently in testing, proposed names, not currently
registered for use in Canada (as of June, 2000)
1 Viper and Meridan are sold as
co-packs containing imazamox and fomesafen (Reflex) or bentazon
(Basagran Forte)
2 Patriot is sold as a premix
containing imazethapyr and atrazine; Cleansweep and Conquest are
sold as co-packs containing imazethapyr and bentazon (Basagran Forte)
or metribuzin respectively.
3 Peak is sold as a co-pack containing
prosulfuron (Peak) and dicamba (Banvel II)
4 Each of the flumetsulam products contain
other active ingredients.
Aromatic Amino Acid Synthesis Inhibitors
Amino Acid Derivatives (Glycines) - Site of Action Group
9
Inhibitors of 5-enolpyruvylshikimimate-3-phosphate synthase (EPSPS)
Plant Injury Symptoms
- Aromatic Amino Acid Inhibitors (EPSP synthase) (phloem mobile):
One of the most "translocatable" herbicides known. Plant
foliage will first yellow (new leaves first) and then turn brown
and die within 10-14 days after herbicide application. Resistance
has been found but is not yet a problem.
Herbicide Breakdown
- Glyphosate is rapidly and tightly adsorbed to soil. There is
no soil activity due to rapid adsorption. Degradation is by microbial
action and rates vary with soil and microbial population. The
long-term degradative process is not apparent in the field in
terms of bioavailability due to its strong adsorption to soil
particles.
- Half life in soil: glyphosate - 47 days
Table 3. Amino Acid Derivatives
Glycines (Group 9)
| Trade Names |
Common Names |
| CREDIT |
glyphosate IPA1 |
| GLYFOS |
glyphosate IPA |
| ROUNDUP*** |
glyphosate IPA |
| VANTAGE*** |
glyphosate IPA |
| VISION*** |
glyphosate IPA |
| TOUCHDOWN*** |
glyphosate TMS2 |
*** Various products and formulations available
1 IPA is the isopropylamine salt of
glyphosate
2 TMS is the trimethylsulfonium salt
of glyphosate also known as sulfosate
Auxinic Herbicides (Growth Regulators)
Site of Action Group 4
Synthetic auxins, specific site(s) unknown.
Plant Injury Symptoms
- Phenoxy acids (highly phloem mobile): Broadleaf plants exhibit
stem twisting and leaf malformations (cupping, crinkling, parallel
veins, leaf strapping). Corn plants exhibit rolled leaves (onion
leafing), fused brace roots, stalk bending (goosenecking) and
brittleness, and missing kernels. Small grains exhibit twisted
flag leaves, sterile florets, or multiple florets, twisted awns
and head malformation. Resistance may occur but is not yet a problem.
- Benzoic acids (highly phloem mobile): Dicamba injury is similar
to that caused by phenoxy acid herbicides but broadleaf plants
may exhibit more cupping than strapping of leaf tissues. May cause
more goosenecking in corn and lodging in small grain (especially
wheat) than phenoxys. Resistance may occur but is not yet a problem.
- Pyridine acids (highly phloem mobile): Pyridines are also known
as Carboxylic acids. Injury similar to phenoxy acid herbicides.
Resistance may occur but is not yet a problem.
Table 4. Auxinic Herbicides
Phenoxy acids (Group 4)
| Trade Names |
Common Names |
| various *** |
2,4-D |
| ESTAMINE |
2,4-D |
| ESTASOL |
2,4-D |
| various *** |
2,4-DB |
| CALIBER |
2,4-DB |
| COBUTOX |
2,4-DB |
| EMBUTOX |
2,4-DB |
| various *** |
dichlorprop |
| various *** |
MCPA |
| various *** |
MCPB |
| CLOVITOX PLUS |
MCPB /MCPA |
| TROPOTOX PLUS |
MCPB /MCPA |
| various *** |
mecoprop |
Benzoic Acids (Group 4)
| Trade Names |
Common Names |
| BANVEL II |
dicamba |
| CADENCE |
dicamba |
| DISTINCT1 |
dicamba |
| various *** |
dicamba |
Pyridine acids (Group 4)
| Trade Names |
Common Names |
| LONTREL |
clopyralid |
| TRANSLINE |
clopyralid |
| FIELDSTAR2 |
clopyralid |
| STRIKER2 |
clopyralid |
| TORDON |
picloram |
| GARLON |
triclopyr |
*** Various products and formulations available
1 Distinct also contains diflufenzopyr
which is an auxin transport inhibitor
2 Fieldstar and Striker also contain
flumetsulam
Herbicide Breakdown
- Phenoxy acids Microbial breakdown in warm, moist soils. Rate
of breakdown increases with increased temperature, moisture, pH
and OM content. Potentially mobile, but leaching is minimized
by rapid degradation.
- Half life in soil:
- 2,4-DB - 5 days
- MCPA - 5-6 days
- dichlorprop - 10 days
- 2,4-D - 10 days
- MCPB - 14 days
- mecoprop - 21 days
- Benzoic acids: Breakdown is primarily due to volatization losses
and microbial degradation. Dicamba is highly mobile in soils,
especially on sandy soils but leaching potential is low to medium
due to rapid degradation. Persists longer under conditions of
low rainfall or soil moisture.
- Half life in soil: dicamba - less than 14 days
- Pyridine acids: Degraded by photodegradation and by microbial
breakdown. They are degraded more slowly than the phenoxys or
benzoics. Clopyralid by microbial breakdown only.
- Half life in soil:
- triclopyr - 30 days
- clopyralid - 40 days
- picloram - 90 days
Pigment Inhibitors (Bleaching Herbicides)
- Triazoles (amitrole): Site of Action Group 11 -
Inhibitors of carotenoid biosynthesis
- Isoxazolidinones (clomazone): Site of Action Group 13
- Inhibitors of carotenoid biosynthesis
- Isoxazoles (isoxaflutole) and Triketones (mesotrione): Site
of Action Group 28 - Inhibitors of p-hydroxyphenyl pyruvate
dioxygenase (HPPD).
Table 5. Pigment Inhibitors
| Trade Names |
Common Names |
| AMITROLE (11) |
amitrole |
| COMMAND (13)** |
clomazone ** |
HPPD (Group 28)
| Trade Names |
Common Names |
| CONVERGE1 |
isoxaflutole |
| not determined |
mesotrione ** |
** currently in testing, proposed names,
not currently registered for use in Canada (as of June, 2000)
1 Converge is sold as a co-pack
containing isoxafluole and atrazine
Plant Injury Symptoms
- Pigment Inhibitors (systemic): Affected plant parts become white
to translucent. Susceptible plants may emerge as white plants
before dying.
Herbicide Breakdown
- Clomazone breakdown is mostly by microbial with some photodegradation.
Amitrole breakdown is unknown. Isoxaflutole by microbial decomposition.
Not yet known to be prone to resistance.
- Half life in soil:
- amitrole - 14 days
- clomazone - 24 days
- isoxaflutole - 28 days
Herbicides Causing Injury to Old Growth and
With the Potential to Move Only Upward
Photosynthesis Inhibitors
- Triazines, Uracils, Phenyl-carbamates, Pyridazinones: Site
of Action Group 5 - Inhibitors of photosynthesis at photosystem
II, Site A. Blocks electron transport and the transfer of light
energy.
- Substituted Ureas: Site of Action Group 7 - Inhibitors
of photosynthesis at photosystem II, Site B. Blocks electron transport
and the transfer of light energy.
- Others - Benzothiadiazoles (bentazon), Nitriles (bromoxynil),
Phenyl-pyridazines (pyridate): Site of Action Group 6
- Inhibitors of photosynthesis at photosystem II, Site
A.
Plant Injury Symptoms
- Triazines (xylem mobile): Translocation occurs only in the xylem
(upwards only). Injury symptoms occur after the cotyledons and
first true leaves emerge. Injury symptoms include yellowing of
the leaf margins or tips and yellowing between the leaf veins
in broadleaf plants. Older and larger leaves are affected first.
Injured leaf tissue eventually turns brown and dies. There is
greater injury on higher pH soils (greater than pH 7.2). Prone
to resistance which can be an agronomic problem.
- Substituted Ureas and Uracils (xylem mobile): Symptoms are the
same as for triazines. Generally not prone to resistance, but
it has been reported with long term repeated use.
- Others - bentazon, bromoxynil, pyridate (contact): Injury is
confined to foliage that has come in contact with the herbicide.
Low doses of these herbicides mimic classical photosynthesis inhibitors.
High doses mimic cell membrane disrupters. Crop oil concentrates
and other additives may intensify injury symptoms. Grass plants
are generally tolerant to the non-systemic photosynthesis inhibitors.
Table 6. Photosynthesis Inhibitors
Triazines (Group 5)
| Trade Names |
Common Names |
| AATREX |
atrazine |
| various *** |
atrazine |
| BLADEX |
cyanazine |
| VELPAR |
hexazinone |
| SENCOR |
metribuzin |
| LEXONE |
metribuzin |
| various *** |
metribuzin |
| GESAGARD |
prometryne |
| SIMADEX |
simazine |
| PRINCEP |
simazine |
Uracils (Group 5)
| Trade Names |
Common Names |
| HYVAR |
bromacil |
| SINBAR |
terbacil |
Phenyl-carbamates (Group 5)
| Trade Names |
Common Names |
| BETANEX |
desmedipham |
| SPIN-AID |
phenmedipham |
Pyridazinones (Group 5)
| Trade Names |
Common Names |
| PYRAMIN |
pyrazon |
Others
| Trade Names |
Common Names |
| BASAGRAN (6) |
bentazon |
| PARDNER (6) |
bromoxynil |
| LENTAGRAN (6) |
pyridate |
Substituted Ureas (Group 7)
| Trade Names |
Common Names |
| KARMEX |
diuron |
| AFOLAN |
linuron |
| LOROX |
linuron |
| PATORAN |
metobromuron |
| AFESIN |
Monolinuron |
*** Various products and formulations
available
Herbicide Breakdown
- Triazines: Breakdown is mainly by microbial action but hydrolysis
is the major contributer to breakdown at low pH. More available
on sandy soils due to fewer adsorption sites and warmer temperatures.
Persistence is greater under dry conditions, cold temperatures
and in sandy soils. Persistence is also greater in soils with
low organic matter, low clay content, and higher pH. Recropping
can be a problem with sensitive species.
- Half life in soil:
- cyanazine - 14 days
- metribuzin - 30-60 days
- atrazine - 60 days
- prometryne - 60 days
- simazine - 60 days
- hexazinone - 90 days
- Substituted Ureas and Uracils: Microbial breakdown is primary
means of dissipation.
- Half life in soil:
- metobromuron - 30 days
- monolinuron - 45-60 days
- linuron - 60 days
- bromacil - 60 days
- diuron - 90 days
- terbacil - 120 days
- Others - bentazon, bromoxynil, pyridate: Mainly by microbial
breakdown.
- Half life in soil:
- bromoxynil - 7 days
- pyridate - 7-21 days
- bentazon - 20 days
- pyrazon - 21 days
- phenmedipham - 25-30 days
- desmedipham - <30 days
Herbicides Applied to the Soil With the
Potential to Injure Emerging Seedlings
Seedling (or Cell) Growth Inhibitors
- Dinitroanalines and Pyridines (dithiopyr):
Site of Action Group 3 - Microtubule assembly inhibitors, tubulin
protein involved in cell division, interrupts mitosis (root inhibitors).
- Carbamothioates and Phosphorodithioates:
Site of Action Group 8 - Conjugation of acetyl co-enzyme A, specific
site unknown (shoot inhibitors).
- Chloroacetamides and Acetamides: Site of Action Group 15 - Conjugation
of acetyl co-enzyme A, specific site unknown (shoot inhibitors).
Plant Injury Symptoms
- Dinitroanalines: Injury symptoms include stunted plants that
do not fully emerge from the soil and short, thick, lateral roots.
Grass (including corn) shoots are short and thick and may appear
red or purple in colour. Broadleaf plants may have swollen and
cracked hypocotyls (area below cotyledons). There is very little
movement of these herbicides within the plant. Some resistance
issues.
- Chloroacetamides (xylem mobile only): Symptoms include stunting
of shoots that result in abnormal seedlings that do not emerge
from the soil. Grasses may leaf-out under ground and the shoots
may be abnormal when leaves do not properly unfurl. Broadleaves
may have crinkled leaves and or a shortened mid-vein which produces
a "draw-string effect" or "heart shaped" leaves.
Not prone to resistance.
- Carbamothioates (xylem mobile only): Carbamothioates are also
known as thiocarbamates. Shoots are stunted and emerge poorly
from the soil. Grasses may fail to emerge from the coleoptile
or may leaf-out underground. Leaf tips may not unfurl from the
coleoptile creating a "buggy whip" effect. Broadleaves
may have crinkled or puckered leaves or the buds may not open.
Not prone to resistance.
Table 7. Seedling Growth Inhibitors
Dinitroanalines (Group 3)
| Trade Names |
Common Names |
| EDGE |
ethalfluralin |
| PROWL |
pendimethalin |
| BONANZA |
trifluralin |
| RIVAL |
trifluralin |
| TREFLAN |
trifluralin |
Pyridine (Group 3)
| Trade Names |
Common Names |
| DIMENSION |
dithiopyr |
Carbamothioates (Group 8)
| Trade Names |
Common Names |
| SUTAN |
butylate |
| RO-NEET |
cycloate |
| ERADICANE |
EPTC |
| EPTAM |
EPTC |
| AVADEX |
triallate |
Phosphorodithioates (Group 8)
| Trade Names |
Common Names |
| BETASAN |
bensulide |
Chloroacetamides (Group 15)
| Trade Names |
Common Names |
| FRONTIER |
dimethenamide |
| AXIOM1 |
flufenacet |
| DUAL |
metolachlor |
Acetamides (Group 15)
| Trade Names |
Common Names |
| DEVRINOL |
Napropamide |
1 Axiom contains both flufenacet
and metribuzin
Herbicide Breakdown
- Dinitroanalines: Breakdown by photodegradation and soil microbes.
Soil incorporation is usually required with these products. Microbial
degradation is more rapid under anaerobic conditions. Persistence
is longer under cool, dry conditions. Enhanced degradation ("history
soils") may occur where microbes can rapidly breakdown herbicide
to reduce efficacy.
- Half life in soil:
- dithiopyr - 17 days
- pendimethalin - 44 days
- trifluralin - 45 days
- ethalfluralin - 60 days
- Chloroacetamides: Mainly by microbial degradation. Longer persistence
under anaerobic and cooler conditions.
- Half life in soil:
- dimethenamide - 20 days
- metolachlor - 30-50 days
- flufenacet - 45-60 days
- napropramide - 70 days
- Carbamothioates: Metabolized by soil microbes. Enhanced degradation
("history soils") may occur after repeated applications
where microbes can rapidly breakdown herbicide thereby reducing
efficacy. Soil incorporation is usually required with these products.
- Half life in soil:
- EPTC - 6 days
- butylate - 13 days
- cycloate - 30 days
- triallate - 82 days
- bensulide - 120 days
Herbicides Causing Immediate Injury With
Little or no Movement
Cell Membrane Disruptes (Contact Herbicides)
- Phosphorylated Amino Acids (also known as Phosphinic Acids):
Site of Action Group 10 - Inhibitors of glutamine synthetase,
also known as inhibitors of ammonia assimilation
- Diphenylethers and Oxadiazoles: Site of Action Group
14 - Inhibitors of protoporphyrinogen oxidase (PPO or
Protox)
- Bipyridiliums: Site of Action Group 22 - Photosystem
I - electron diverters
Plant Injury Symptoms
- Phosphorylated Amino Acids (contact with limited phloem/xylem
mobility): Chlorosis and wilting usually occur within 3-5 days
followed by necrosis within 1-2 weeks. Symptoms occur faster in
bright sunlight and high humidity. Not prone to resistance.
- Bipyridiliums (contact): Plant leaves will have a limp, water
soaked appearance, which is followed by browning of the leaf tissue.
Drift injury appears as speckling on leaf tissue.
- Diphenylethers (contact): Plant leaves turn yellow then brown
and die. Reddish-colored spotting on the leaf surface may appear
shortly after application. Plants that do not die may be stunted
for a week or so. Crop oils and other additives may increase plant
injury. Not prone to resistance.
- Oxadiazoles (contact): Seedlings emerge from treated soil and
then wilt and die. Foliar applications cause chlorosis and die
within 1-2 days. Not prone to resistance.
Herbicide Breakdown
- Phosphorylated Amino Acids: Rapidly degraded by soil microbes.
- Diphenylethers: Both photo and microbial degradation. Fomesafen
degrades faster under anaerobic conditions.
- Half life in soil:
- aciflurofen - 14-60 days
- oxyfluorfen - 35 days
- fomesafen - 100 days
- Bipyridiliums: Strongly adsorbed to clay particles. Not available
for plant uptake or microbial breakdown.
- Half life in soil:
- difenzoquat - <4 weeks
- diquat - 1000 days
- paraquat - 1000 days
- Oxadiazoles (contact): Strongly adsorbed by soil colloids.
Table 8. Cell Membrane Disrupters
Phosphorylated Amino Acid (Group 10)
| Trade Names |
Common Names |
| IGNITE |
Glufosinate ammonium |
| LIBERTY |
Glufosinate ammonium |
Diphenylethers (Group 14)
| Trade Names |
Common Names |
| BLAZER |
aciflurofen |
| REFLEX |
fomesafen |
| GOAL |
oxyfluorfen |
Oxadiazoles (Group 14)
| Trade Names |
Common Names |
| RONSTAR |
oxydiazon |
Bipyridiliums (Group 22)
| Trade Names |
Common Names |
| AVENGE |
difenzoquat |
| GRAMOXONE |
paraquat |
| REGLONE |
diquat |
Other Herbicides
- Casoron (xylem mobile): Site of Action Group 20 - chemical family
Nitriles, mode of action is the inhibition of cell wall (cellulose)
synthesis. Blocks electron transport and the transfer of light
energy. Diclobenil is a systemic herbicide and when soil applied
susceptible seedlings usually do not emerge.
- Avenge - difenzoquat (xylem mobile): Site of Action Group 8
- chemical family Pyrazolium, mode of action is largely unknown.
- Injury symptoms of chlorosis and necrosis appear within 3-7
days. Some resistant species but not a wide spread agronomic problem.
- Alanap - napthalam: Site of action Group 19 - chemical family
Phthalamates, mode of action is the inhibition of auxin transport.
Movement within the plant is somewhat limited.
- Injury Symptoms - Strong epinasty and antigeotropic response,
abolishing the normal curvature of roots toward the ground and
of shoots toward light.
- Microbial breakdown
Acknowledgements
Thanks to Dr. J.C. Hall, Department of Environmental Biology, University
of Guelph, for his comments on this Factsheet.
Resources
Herbicide Mode of Action and Injury Symptoms, Jeffery L. Gunsolus
and William S. Curran, North Central Regional Publication 377, 1994.
Herbicide Mode of Action and Injury Symptoms, CD-ROM, Jeffery L.
Gunsolus et al, University of Minnesota Extension Service, 1999
Herbicide Mode-of-Action Categories by Merrill A. Ross and Thomas
N. Jordan, Purdue University, 1999.
Classification of Herbicides According to Mode of Action, April
1999, Robert Schmidt,
WSSA Herbicide Handbook, Weed Science Society of America, 1994
and Supplement 1998.
