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
- Related Links
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)
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.
- 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)
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.
Half life in soil: glufosinate - 7 days
- 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.
Half life in soil: oxydiazon - 60 days
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.
Half life in ssoil: difenzoquat - <4 weeks
- 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
Half life in soil: napthalam - 14 days
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.
