Herbicide Mode of Action Categories


Factsheet - ISSN 1198-712X   -   Copyright Queen's Printer for Ontario
Agdex#: 641
Publication Date: 05/00
Order#: 00-061
Last Reviewed: 08/09
History: Original Factsheet
Written by: Hugh Martin - Program Lead, Organic Crop Production/OMAF

Table of Contents

  1. Introduction
  2. Herbicides Causing Injury to New Growth and with the Potential to Move From Leaves to Roots
  3. Herbicides Causing Injury to Old Growth and With the Potential to Move Only Upward
  4. Herbicides Applied to the Soil With the Potential to Injure Emerging Seedlings
  5. Herbicides Causing Immediate Injury With Little or no Movement
  6. Acknowledgements
  7. 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.

 


For more information:
Toll Free: 1-877-424-1300
E-mail: ag.info.omafra@ontario.ca