Herbicide Mode of Action Categories


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/OMAFRA

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.
- 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 soil:
- 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:
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E-mail: ag.info.omafra@ontario.ca

Ministry of Agriculture, Food and Rural Affairs