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Table 1. Herbicide MOA classification system. HRAC WSSA group group Mode of action Chemical family Active ingredients E 14 Inhibition of Diphenylethers acifluorfen proto- fomesafen porphyrinogen lactofen oxidase oxyfluorfen (PPO, or Protox)

Table 1. Herbicide MOA classification system. HRAC WSSA group

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Page 1: Table 1. Herbicide MOA classification system. HRAC WSSA group

Table 1. Herbicide MOA classification system.

HRAC WSSA

group group Mode of action Chemical family Active ingredients

E 14 Inhibition of Diphenylethers acifluorfen

proto- fomesafen

porphyrinogen lactofen

oxidase oxyfluorfen

(PPO, or

Protox)

Page 2: Table 1. Herbicide MOA classification system. HRAC WSSA group

O NO2

Basic structure of a diphenylether

Two phenyl rings joined by an ether bridge,

and a nitro group on one of the phenyl rings.

Page 3: Table 1. Herbicide MOA classification system. HRAC WSSA group

Mode of Action of Diphenylethers

• Inhibit porphyrin synthesis pathway, the

pathway for formation of chlorophyll and

cytochromes

• Specifically, they inhibit protoporphyrinogen

IX oxidase (PPO or PROTOX), the enzyme

that converts protoporphyrinogen IX to

protoporphyrin IX.

• Proto accumulates, free radicals, oxidative

breakdown of membranes

Page 4: Table 1. Herbicide MOA classification system. HRAC WSSA group

Diphenylether Herbicides

• Behave as contacts.

• Typically applied POST, primarily for

broadleaf weeds.

• Soil persistence varies.

• Very little soil activity with acifluorfen

and lactofen.

• Fomesafen and oxyfluorfen have soil

activity.

Page 5: Table 1. Herbicide MOA classification system. HRAC WSSA group

Table 1. Herbicide MOA classification system.

HRAC WSSA

group group Mode of action Chemical family Active ingredients

E 14 Inhibition of N-phenyl- flumioxazin

proto- phthalimides flumiclorac-pentyl ester

porphyrinogen

oxidase

(PPO, Protox)

Page 6: Table 1. Herbicide MOA classification system. HRAC WSSA group

Flumiclorac-pentyl ester

Flumioxazin

Page 7: Table 1. Herbicide MOA classification system. HRAC WSSA group

Flumioxazin and Flumiclorac-pentyl Ester

• Foliar absorbed; very limited translocation.

• Act as contacts.

• No soil activity with flumiclorac-pentyl

ester; flumioxazin controls weeds PRE for

30 days or more (depending upon rate).

Page 8: Table 1. Herbicide MOA classification system. HRAC WSSA group

Table 1. Herbicide MOA classification system.

HRAC WSSA

group group Mode of action Chemical family Active ingredients

E 14 Inhibition of Oxadiazoles oxadiazon

proto-

porphyrinogen

oxidase

(PPO, Protox)

Page 9: Table 1. Herbicide MOA classification system. HRAC WSSA group

oxadiazon

Page 10: Table 1. Herbicide MOA classification system. HRAC WSSA group

Table 1. Herbicide MOA herbicide classification system.

HRAC WSSA

group group Mode of action Chemical family Active ingredients

E 14 Inhibition of Phenylpyrazoles Fluthiacet-methyl

proto-

porphyrinogen

oxidase

(PPO, Protox)

Page 11: Table 1. Herbicide MOA classification system. HRAC WSSA group

Table 1. Herbicide MOA herbicide classification system.

HRAC WSSA

group group Mode of action Chemical family Active ingredients

E 14 Inhibition of Triazolinones carfentrazone-ethyl

proto- sulfentrazone

porphyrinogen

oxidase

(PPO, Protox)

Page 12: Table 1. Herbicide MOA classification system. HRAC WSSA group

N N

N

R

R

R

O

Basic structure of a triazolinone

Five-membered ring containing three nitrogens and an

oxygen double-bonded to the ring.

Page 13: Table 1. Herbicide MOA classification system. HRAC WSSA group

Triazolinone Herbicides

1. Carfentrazone-ethyl is applied POST or POST-directed only;

behaves as contact; no soil activity.

2. Sulfentrazone applied PPI or PRE. Apoplastic translocation.

Currently no POST labels, but it can also be absorbed by

foliage. Relatively long activity in soil; some rotational

restrictions apply to NC crops.

3. Triazolinone herbicides primarily control broadleaf weeds, but

sulfentrazone is extremely good on nutsedge species.

Page 14: Table 1. Herbicide MOA classification system. HRAC WSSA group

Uses of Sulfentrazone

2. Packaged mixtures

c. Surge

sulfentrazone + 2,4-D + MCPP + dicamba

POST control of broadleaf weeds in turf

Page 15: Table 1. Herbicide MOA classification system. HRAC WSSA group

PPO inhibitors

Lactofen, A. York, NCSU Acifluorfen, A. York, NCSU

Fomesafen, A. York, NCSU Flumiclorac, A. York, NCSU

Page 16: Table 1. Herbicide MOA classification system. HRAC WSSA group

Carfentrazone, A. York, NCSU

Carfentrazone, A. York, NCSU

Acifluorfen, A. York, NCSU

PPO inhibitors

Page 17: Table 1. Herbicide MOA classification system. HRAC WSSA group

Aim post-directed

Page 18: Table 1. Herbicide MOA classification system. HRAC WSSA group

A. York, NCSU

PPO inhibitors

Flumioxazin preemergence

Page 19: Table 1. Herbicide MOA classification system. HRAC WSSA group

Table 1. Herbicide MOA classification system.

HRAC WSSA

group group Mode of action Chemical family Active ingredients

F1 12 Inhibition of Pyridazinones norflurazon

carotenoid

biosynthesis

at PDS

F2 28 at 4-HPPD Triketones mesotrione, tembotrione

Benzoyl pyrazole topramezone

F3 13 unknown Isoxazolidinones clomazone

Page 20: Table 1. Herbicide MOA classification system. HRAC WSSA group

Bleachers

Pyridazinones, triketones, and isoxazolidinones (and

others not used in NC) are bleachers.

These herbicides inhibit biosynthesis of carotenoids

(yellow, orange pigments). In absence of carotenoids,

chlorophyll is photodegraded, resulting in bleached

plant. White or pale yellow plants.

Page 21: Table 1. Herbicide MOA classification system. HRAC WSSA group

Table 1. Herbicide MOA classification system.

HRAC WSSA

group group Mode of action Chemical family Active ingredients

F1 12 Inhibition of Pyridazinones norflurazon

carotenoid

biosynthesis

at PDS

F2 28 at 4-HPPD Triketones mesotrione, tembotrione

Benzoyl pyrazole topramezone

F3 13 unknown Isoxazolidinones clomazone

Page 22: Table 1. Herbicide MOA classification system. HRAC WSSA group

R1 R2

C

O

Ketone: a carbonyl carbon bonded to two

carbon atoms.

Page 23: Table 1. Herbicide MOA classification system. HRAC WSSA group

Table 1. Herbicide MOA classification system.

HRAC WSSA

group group Mode of action Chemical family Active ingredients

F1 12 Inhibition of Pyridazinones norflurazon

carotenoid

biosynthesis

at PDS

F2 28 at 4-HPPD Triketones mesotrione, tembotrione

Benzoyl pyrazole topramezone

F3 13 unknown Isoxazolidinones clomazone

Page 24: Table 1. Herbicide MOA classification system. HRAC WSSA group

Clomazone -- Isoxazolidinone family

Page 25: Table 1. Herbicide MOA classification system. HRAC WSSA group

Clomazone

• Absorbed by roots of dicots; by emerging coleoptiles of grasses

• Apoplastically translocated

• Relatively long life in soil; gives season-long control;

may carryover to susceptible crops

• Somewhat volatile. Do not lose enough via volatilization

to adversely affect weed control (i.e., it works well PRE).However, bleaching on off-target vegetation has been a serious concern. Numerous precautions on label, plusbuffer zones.

• Controls annual grasses (except Texas panicum). Also

very effective on selected broadleaf weeds.

Page 26: Table 1. Herbicide MOA classification system. HRAC WSSA group

Uses of Clomazone

• PPI or PRE (before or after transplanting) on

tobacco.

• PRE on cotton. Must be used in conjunction

with in-furrow application of phorate or

disulfoton. No longer used in NC.

• PRE on soybeans. No longer used in NC.

• PRE on several vegetable crops. Lot used in

sweet potatoes.

Page 27: Table 1. Herbicide MOA classification system. HRAC WSSA group

Culpepper, Univ. GA

Norflurazon carryover on cabbage

Page 28: Table 1. Herbicide MOA classification system. HRAC WSSA group

York, NCSU

Norflurazon

Page 29: Table 1. Herbicide MOA classification system. HRAC WSSA group

Clomazone

A. York, NCSU

Clomazone

+

phorate

Clomazone

+

aldicarb

Page 30: Table 1. Herbicide MOA classification system. HRAC WSSA group

Clomazone

A. York, NCSU

Page 31: Table 1. Herbicide MOA classification system. HRAC WSSA group

Clomazone drift

Page 32: Table 1. Herbicide MOA classification system. HRAC WSSA group

Mesotrione

A. York, NCSU

Page 33: Table 1. Herbicide MOA classification system. HRAC WSSA group

Mesotrione

A. York, NCSU

Page 34: Table 1. Herbicide MOA classification system. HRAC WSSA group

Table 1. Herbicide MOA herbicide classification system.

HRAC WSSA

group group Mode of action Chemical family Active ingredients

G 9 Inhibition of Glycines glyphosate

EPSP

synthase

Page 35: Table 1. Herbicide MOA classification system. HRAC WSSA group

Glyphosate Mechanism of Action

• Inhibits 5-enolpyruvyl shikimate-3-phosphate

(EPSP) synthase

• EPSP synthase is an enzyme in the shikimate

pathway leading to biosynthesis of the aromatic

amino acids phenylalanine, tryptophan, and tyrosine.

• Plants die slowly (7 to 14 days). Terminal

becomes chlorotic, plants cease growth, and

slowly die.

Page 36: Table 1. Herbicide MOA classification system. HRAC WSSA group

Characteristics of Glyphosate

• Very low mammalian toxicity

• Very tightly bound to soil; no soil activity; no leaching.

• Very good environmental profile.

• Applied POST to weeds, foliar absorption, symplastic

translocation

• Very limited metabolism in plants

• Broad spectrum control of grasses and broadleaf weeds;

but some species only marginally controlled or not

controlled

• Resistant biotypes of weeds are known to occur

Page 37: Table 1. Herbicide MOA classification system. HRAC WSSA group

HO -

O

C -

H

C -

H

H

N -

H

C -

H

O

P -

OH

OH

Glyphosate acid

Page 38: Table 1. Herbicide MOA classification system. HRAC WSSA group

Glyphosate Formulations

Glyphosate is formulated as one of three salts:

• diammonium salt (currently not on market)

• potassium salt

• isopropylamine salt

Page 39: Table 1. Herbicide MOA classification system. HRAC WSSA group

HO -

O

C -

H

C -

H

H

N -

H

C -

H

O

P -

OH

OH

H3N - O -

O

C -

H

C -

H

H

N -

H

C -

H

O

P -

OH

O - NH3

Diammonium salt of glyphosate

Glyphosate acid

Page 40: Table 1. Herbicide MOA classification system. HRAC WSSA group

HO -

O

C -

H

C -

H

H

N -

H

C -

H

O

P -

OH

OH

HO -

O

C -

H

C -

H

H

N -

H

C -

H

O

P -

OH

CH3

O - NH2 - CH

CH3

Isopropylamine salt of glyphosate

Glyphosate acid

Page 41: Table 1. Herbicide MOA classification system. HRAC WSSA group

HO -

O

C -

H

C -

H

H

N -

H

C -

H

O

P -

OH

OH

HO -

O

C -

H

C -

H

H

N -

H

C -

H

O

P -

OH

O - K

Potassium salt of glyphosate

Glyphosate acid

Page 42: Table 1. Herbicide MOA classification system. HRAC WSSA group

Comparing Glyphosate Formulations

• At equivalent rates, research has shown no

practical differences in crop tolerance or weed control

among the three basic formulations or among

the many trade names available.

• Exception has been two brands containing

isopropylamine salt of glyphosate. Contact burn

on cotton foliage has been observed. Thought to

be due to adjuvants or contaminants in the formulated

product, and not due to glyphosate per se.

Page 43: Table 1. Herbicide MOA classification system. HRAC WSSA group

Untreated

Clearout 41 Plus

Page 44: Table 1. Herbicide MOA classification system. HRAC WSSA group

Grower field, Clearout 41 Plus, 5 DAT

Page 45: Table 1. Herbicide MOA classification system. HRAC WSSA group

Glyphosate drift on non-RR corn

Page 46: Table 1. Herbicide MOA classification system. HRAC WSSA group

Glyphosate drift on non-RR corn

Page 47: Table 1. Herbicide MOA classification system. HRAC WSSA group

Glyphosate on non-RR corn; sprayer contamination

Page 48: Table 1. Herbicide MOA classification system. HRAC WSSA group

Glyphosate on non-RR corn; sprayer contamination

Page 49: Table 1. Herbicide MOA classification system. HRAC WSSA group

Glyphosate applied to non-RR corn

Page 50: Table 1. Herbicide MOA classification system. HRAC WSSA group

Glyphosate drift

Univ. Wisconsin

Page 51: Table 1. Herbicide MOA classification system. HRAC WSSA group

Univ. Wisconsin

Glyphosate drift

Page 52: Table 1. Herbicide MOA classification system. HRAC WSSA group

Double rate of glyphosate on RR soybean

Page 53: Table 1. Herbicide MOA classification system. HRAC WSSA group

Glyphosate sprayer contamination

N. Porter, UniroyalN. Porter, Uniroyal

Page 54: Table 1. Herbicide MOA classification system. HRAC WSSA group

Glyphosate on RR cotton

Page 55: Table 1. Herbicide MOA classification system. HRAC WSSA group

Glyphosate on RR cotton

Page 56: Table 1. Herbicide MOA classification system. HRAC WSSA group

Glyphosate on RR cotton

Page 57: Table 1. Herbicide MOA classification system. HRAC WSSA group

Glyphosate overtop RR cotton after 4-leaf stage

Page 58: Table 1. Herbicide MOA classification system. HRAC WSSA group

Table 1. HRAC herbicide classification system.

HRAC WSSA

group group Mode of action Chemical family Active ingredients

H 10 Inhibition of Phosphinic acids glufosinate-ammonium

glutamine

synthase

Page 59: Table 1. Herbicide MOA classification system. HRAC WSSA group

Glufosinate acid

Glufosinate-ammonium

Page 60: Table 1. Herbicide MOA classification system. HRAC WSSA group

Glufosinate Mode of Action

Inhibits enzyme glutamine synthetase.

NH3 accumulates, which is toxic.

Glutamic acid + glutamine

NH3

amino acids

Page 61: Table 1. Herbicide MOA classification system. HRAC WSSA group

Glufosinate

• Weakly adsorbed to soil; very rapidly degraded; no soil activity.

• Applied postemergence.

• Limited (localized) translocation. Acts much like a contact.

• Controls most annual broadleaf weeds; marginal onAmaranthus.

• Controls annual grasses if treated when small; exception is goosegrass.

• Does not control nutsedge, perennial broadleaf weeds, or bermudagrass. Controls johnsongrass with multiple applications.

• Liberty Link crops (transgenic, resistant to glufosinate) very tolerant of glufosinate

Page 62: Table 1. Herbicide MOA classification system. HRAC WSSA group

Glufosinate

Univ. Wisconsin

A. York, NCSU

A. York, NCSU

Page 63: Table 1. Herbicide MOA classification system. HRAC WSSA group

Glufosinate

A. York, NCSU

A. York, NCSU

Univ. Wisconsin

Page 64: Table 1. Herbicide MOA classification system. HRAC WSSA group

Table 1. HRAC herbicide classification system.

HRAC WSSAgroup group Mode of action Chemical family Active ingredients

K1 3 Microtubule Dinitroanilines benefin

assembly ethalfluralin

inhibition oryzalin

pendimethalin

prodiamine

trifluralin

Pyridines dithiopyr

Benzamides pronamide

Benzene- DCPA

dicarboxylic

acids

Page 65: Table 1. Herbicide MOA classification system. HRAC WSSA group

H-N-H

NO2NO2

Basic structure of a dinitroaniline

Aniline ring with nitro group at 2- and 6-position of ring

Page 66: Table 1. Herbicide MOA classification system. HRAC WSSA group

Dinitroanilines -- Mode of Action

• Seedling growth inhibitors.

• Inhibit root or shoot development (depending upon site of absorption) by interfering with cell division in meristematic areas.

• Specifically, dinitroanilines interfere with microtubule assembly. Prevent normal function of spindle fibers during mitosis.

Page 67: Table 1. Herbicide MOA classification system. HRAC WSSA group
Page 68: Table 1. Herbicide MOA classification system. HRAC WSSA group

Characteristics of Dinitroanilines

• Commonly referred to as DNAs.

• They are yellow. Some DNA compounds

used in dye industry. Commonly referred

to as “yellow herbicides”.

• Nearly immobile in soil. Low water

solubility and tightly adsorbed.

• DNAs, except oryzalin, are relatively

volatile. Also subject to photodegradation.

Page 69: Table 1. Herbicide MOA classification system. HRAC WSSA group

Characteristics of Dinitroanilines

• Absorbed by roots of dicots, by

emerging coleoptile of grasses.

Page 70: Table 1. Herbicide MOA classification system. HRAC WSSA group
Page 71: Table 1. Herbicide MOA classification system. HRAC WSSA group

Characteristics of Dinitroanilines

• Absorbed by roots of dicots, by

emerging coleoptile of grasses.

• Non-mobile in plants.

• No postemergence activity.

• Symptoms are swollen root tips, or

club-shaped roots. Lateral root growth

inhibited more than tap root growth.

Page 72: Table 1. Herbicide MOA classification system. HRAC WSSA group

Univ. Wisconsin

Root pruning with DNA’s

Page 73: Table 1. Herbicide MOA classification system. HRAC WSSA group

Root pruning

with DNA’s

Page 74: Table 1. Herbicide MOA classification system. HRAC WSSA group

Stunting by DNA herbicide

A. York, NCSU

Page 75: Table 1. Herbicide MOA classification system. HRAC WSSA group

Characteristics of Dinitroanilines

• Relatively long soil residual. Season-long

control of susceptible species if applied

properly.

• Generally do not have carryover concerns,

but there have been exceptions. Hard pan

tends to complicate carryover problems.

• Control annual grasses and certain small-

seeded broadleaf weeds.

Page 76: Table 1. Herbicide MOA classification system. HRAC WSSA group

Table 1. HRAC herbicide classification system.

HRAC WSSAgroup group Mode of action Chemical family Active ingredients

K1 3 Microtubule Dinitroanilines benefin

assembly ethalfluralin

inhibition oryzalin

pendimethalin

prodiamine

trifluralin

Pyridines dithiopyr

Benzamides pronamide

Benzene- DCPA

dicarboxylic

acids

Page 77: Table 1. Herbicide MOA classification system. HRAC WSSA group

N

Pyridine

Pyridine herbicides consist of pyridine ring with various

substituent groups off the ring

Page 78: Table 1. Herbicide MOA classification system. HRAC WSSA group

Table 1. HRAC herbicide classification system.

HRAC WSSAgroup group Mode of action Chemical family Active ingredients

K1 3 Microtubule Dinitroanilines benefin

assembly ethalfluralin

inhibition oryzalin

pendimethalin

prodiamine

trifluralin

Pyridines dithiopyr

Benzamides pronamide

Benzene- DCPA

dicarboxylic

acids

Page 79: Table 1. Herbicide MOA classification system. HRAC WSSA group

pronamide

Page 80: Table 1. Herbicide MOA classification system. HRAC WSSA group

Table 1. HRAC herbicide classification system.

HRAC WSSAgroup group Mode of action Chemical family Active ingredients

K1 3 Microtubule Dinitroanilines benefin

assembly ethalfluralin

inhibition oryzalin

pendimethalin

prodiamine

trifluralin

Pyridines dithiopyr

Benzamides pronamide

Benzene- DCPA

dicarboxylic

acids

Page 81: Table 1. Herbicide MOA classification system. HRAC WSSA group

DCPA

Page 82: Table 1. Herbicide MOA classification system. HRAC WSSA group

Table 1. Herbicide MOA classification system.

HRAC WSSAgroup group Mode of action Chemical family Active ingredients

K3 15 Inhibition of Chloroacetamides acetochlor

cell division alachlor

(inhibition of dimethenamid-P

VLCFA) metolachlor

Acetamides napropamide

Oxyacetamides flufenacet

Page 83: Table 1. Herbicide MOA classification system. HRAC WSSA group

Mode of Action

Acetamides

Chloroacetamides

Oxyacetamides

Seedling shoot growth

inhibitors. Impact several

processes in plants. Proposed

mechanism of action is

inhibition of VLCFAs.

Page 84: Table 1. Herbicide MOA classification system. HRAC WSSA group

Characteristics of Chloroacetamides

• Applied PPI or PRE. Occasionally applied POST,

but activity is preemergence on weeds.

• Control annual grasses and some small-seeded

broadleaf weeds; most suppress yellow nutsedge.

• Absorbed by roots of dicots, emerging shoots of grasses.

• Relatively mobile in soil; sometimes found in

ground water.

• Relatively short persistence; 4 to 8 weeks of

control; no carryover problems.

Page 85: Table 1. Herbicide MOA classification system. HRAC WSSA group

Metolachlor

O

C CH2 Cl

N

CH CH2 O CH3

CH3

*

*

Metolachlor has a chiral center and a chiral axis.

CH2 CH3

CH3

Page 86: Table 1. Herbicide MOA classification system. HRAC WSSA group

Table 1. Herbicide MOA classification system.

HRAC WSSAgroup group Mode of action Chemical family Active ingredients

K3 15 Inhibition of Chloroacetamides acetochlor

cell division alachlor

(inhibition of dimethenamid-P

VLCFA) metolachlor

Acetamides napropamide

Oxyacetamides flufenacet

Page 87: Table 1. Herbicide MOA classification system. HRAC WSSA group

napropamide

Page 88: Table 1. Herbicide MOA classification system. HRAC WSSA group

Table 1. Herbicide MOA classification system.

HRAC WSSAgroup group Mode of action Chemical family Active ingredients

K3 15 Inhibition of Chloroacetamides acetochlor

cell division alachlor

(inhibition of dimethenamid-P

VLCFA) metolachlor

Acetamides napropamide

Oxyacetamides flufenacet

Page 89: Table 1. Herbicide MOA classification system. HRAC WSSA group

Chloroacetamides

Page 90: Table 1. Herbicide MOA classification system. HRAC WSSA group

Chloroacetamides

Dewey Lee, UGA

Page 91: Table 1. Herbicide MOA classification system. HRAC WSSA group

Purdue Univ.

Chloroacetamides

Leafing out underground

Page 92: Table 1. Herbicide MOA classification system. HRAC WSSA group

A. York, NCSU

Chloroacetamides

Page 93: Table 1. Herbicide MOA classification system. HRAC WSSA group

Metolachlor preemergence

Page 94: Table 1. Herbicide MOA classification system. HRAC WSSA group

Chloroacetamides

A. York, NCSU

Page 95: Table 1. Herbicide MOA classification system. HRAC WSSA group

Table 1. Herbicide MOA classification system.

HRAC WSSAgroup group Mode of action Chemical family Active ingredients

L 20 Inhibition of Nitriles dichlobenil

cell wall

(cellulose)

synthesis

21 Benzamides isoxaben

Page 96: Table 1. Herbicide MOA classification system. HRAC WSSA group

Cl Cl

C N

dichlobenil

Page 97: Table 1. Herbicide MOA classification system. HRAC WSSA group

Table 1. Herbicide MOA classification system.

HRAC WSSAgroup group Mode of action Chemical family Active ingredients

L 20 Inhibition of Nitriles dichlobenil

cell wall

(cellulose)

synthesis

21 Benzamides isoxaben

Page 98: Table 1. Herbicide MOA classification system. HRAC WSSA group

Table 1. Herbicide MOA classification system.

HRAC WSSAgroup group Mode of action Chemical family Active ingredients

N 8 Inhibition of Thiocarbamates butylate

lipid synthesis EPTC

(not ACCase pebulate*

inhibition) vernolate*

Phosphoro- bensulide

dithioates

Benzofurans ethofumesate

* No longer marketed

Page 99: Table 1. Herbicide MOA classification system. HRAC WSSA group

R1 O

N - C - S - R3

R2

Basic structure of

a thiocarbamate

Page 100: Table 1. Herbicide MOA classification system. HRAC WSSA group

Thiocarbamates

1. Exact site of action unknown. Inhibit lipid synthesis, but not at ACCase

2. Control annual grasses, certain small-seeded broadleaf weeds, and nutsedge

3. Primarily absorbed by coleoptile of grasses

4. Highly volatile; incorporate immediately

5. Short persistence. Control for 3-6 wk or less.

6. May have accelerated degradation

7. Easily leached

Page 101: Table 1. Herbicide MOA classification system. HRAC WSSA group

Thiocarbamates

Page 102: Table 1. Herbicide MOA classification system. HRAC WSSA group

Table 1. HRAC herbicide classification system.

HRAC WSSAgroup group Mode of action Chemical family Active ingredients

N 8 Inhibition of Thiocarbamates butylate

lipid synthesis EPTC

(not ACCase pebulate

inhibition) vernolate

Phosphoro- bensulide

dithioates

Benzofurans ethofumesate

Page 103: Table 1. Herbicide MOA classification system. HRAC WSSA group

bensulide

Page 104: Table 1. Herbicide MOA classification system. HRAC WSSA group

Table 1. HRAC herbicide classification system.

HRAC WSSAgroup group Mode of action Chemical family Active ingredients

N 8 Inhibition of Thiocarbamates butylate

lipid synthesis EPTC

(not ACCase pebulate

inhibition) vernolate

Phosphoro- bensulide

dithioates

Benzofurans ethofumesate

Page 105: Table 1. Herbicide MOA classification system. HRAC WSSA group

Table 1. HRAC herbicide classification system.

HRAC WSSAgroup group Mode of action Chemical family Active ingredients

O 4 Act as Phenoxy- 2,4-D

synthetic carboxylic-acids 2,4-DB

auxins 2,4-DP (dichlorprop)

MCPA

MCPP (mecoprop)Benzoic acids dicamba

Pyridine clopyralid

carboxylic acids fluroxypyrpicloramtriclopyraminopyralid

Quinoline quinclorac

carboxylic acids

Page 106: Table 1. Herbicide MOA classification system. HRAC WSSA group

Mode of Action

Phenoxy-carboxylic-acids Benzoic acids

Pyridine carboxylic acids Quinoline carboxylic acids

Act as synthetic auxins. Exact mode of action unknown.

Involves interference with nucleic acid metabolism and

disruption of normal transport systems through induced

massive cell proliferation.

Page 107: Table 1. Herbicide MOA classification system. HRAC WSSA group

O

O - (CH2)i - C - OH

Basic structure of a phenoxy-carboxylic acid

Page 108: Table 1. Herbicide MOA classification system. HRAC WSSA group

Phenoxy-carboxylic acid herbicides

• Typically applied POST to weeds.

• Absorbed by foliage. Can also be absorbed by roots

from soil.

• Systemic in plants, moving in both apoplast and symplast.

• Selective on grasses; most dicots are sensitive.

• Very weakly bound by soil. Readily leached.

• Short soil residual; average half-life 5 to 10 days.

• Formulated as salts or esters.

Page 109: Table 1. Herbicide MOA classification system. HRAC WSSA group

O

O - CH2 - C - OH

O CH3

O - CH2 - C - O - NH

CH3

O CH2 - CH3

O - CH2 - C - O - CH2 - CH - CH2 - CH2 - CH2 -CH3

isooctyl (2-ethylhexyl) ester of 2,4-D

2,4-D acid dimethylamine salt of 2,4-D

Page 110: Table 1. Herbicide MOA classification system. HRAC WSSA group

Practical differences in esters and amines salts of 2,4-D

1. Amines form solutions with water; esters form emulsions.

2. Esters mix well with liquid N, amines do not. Must

premix amines in water, maintain good agitation.

3. Esters more effective in cool weather; may be more

effective on perennials.

4. Esters absorbed better by waxy leaves.

5. Esters less subject to washoff; less water soluble.

6. Amines easier to clean from sprayer.

7. Esters subject to vapor drift.

Page 111: Table 1. Herbicide MOA classification system. HRAC WSSA group

Spray Drift vs. Vapor Drift

• Spray drift can occur with any pesticide sprayed

• Vapor drift occurs with volatile herbicides

• Spray drift is typically short distance

• Vapor drift can be long distance

• Some crops, especially cotton and tomatoes,

are very sensitive to 2,4-D

• Ester formulations of 2,4-D, even though they are

“low volatile” esters, are still volatile

• Ester formulations should not be used with 1 mile

of cotton and other sensitive crops

Page 112: Table 1. Herbicide MOA classification system. HRAC WSSA group

Univ. Wisconsin

2,4-D Postemergence

Page 113: Table 1. Herbicide MOA classification system. HRAC WSSA group

2,4-D

A. York, NCSU

Purdue Univ.

Univ. Wisconsin

Page 114: Table 1. Herbicide MOA classification system. HRAC WSSA group

Epinastic Response

to 2,4-D and 2,4-DB

A. York, NCSU

Page 115: Table 1. Herbicide MOA classification system. HRAC WSSA group

Soybean leaf distortion by 2,4-D

A. York, NCSU Purdue Univ.

Page 116: Table 1. Herbicide MOA classification system. HRAC WSSA group

Cotton leaf distortion by 2,4-D

A. York, NCSU

A. York, NCSU

Page 117: Table 1. Herbicide MOA classification system. HRAC WSSA group
Page 118: Table 1. Herbicide MOA classification system. HRAC WSSA group

2,4-D sprayer

contamination

on tobacco

A. York, NCSU

Page 119: Table 1. Herbicide MOA classification system. HRAC WSSA group

Malformed wheat heads

2,4-D

Page 120: Table 1. Herbicide MOA classification system. HRAC WSSA group

Table 1. HRAC herbicide classification system.

HRAC WSSAgroup group Mode of action Chemical family Active ingredients

O 4 Act as Phenoxy- 2,4-D

synthetic carboxylic-acids 2,4-DB

auxins 2,4-DP (dichlorprop)

MCPA

MCPP (mecoprop)Benzoic acids dicamba

Pyridine clopyralid

carboxylic acids fluroxypyrpicloramtriclopyraminopyralid

Quinoline quinclorac

carboxylic acids

Page 121: Table 1. Herbicide MOA classification system. HRAC WSSA group

Dicamba

1. Little binding to soil, readily leached

2. Short soil half-life, usually less than 14 days

3. Can be absorbed by roots, apoplastically translocated

4. Usually applied POST; readily absorbed by foliage,

symplastically translocated

5. Controls dicots, activity on some monocots (such as

wild garlic), little to no activity on grasses

6. Tobacco, soybeans, and most other broad leaf crops

very sensitive

Page 122: Table 1. Herbicide MOA classification system. HRAC WSSA group

A. York, NCSU

Dicamba

Page 123: Table 1. Herbicide MOA classification system. HRAC WSSA group

Leaf cupping by dicamba

University of Missouri

Kansas State Univ.

A. York, NCSU

Page 124: Table 1. Herbicide MOA classification system. HRAC WSSA group

“Cobra-hood” caused by

dicamba or picloram

Page 125: Table 1. Herbicide MOA classification system. HRAC WSSA group

Univ. Missouri

dicamba

Page 126: Table 1. Herbicide MOA classification system. HRAC WSSA group

Table 1. HRAC herbicide classification system.

HRAC WSSAgroup group Mode of action Chemical family Active ingredients

O 4 Act as Phenoxy- 2,4-D

synthetic carboxylic-acids 2,4-DB

auxins 2,4-DP (dichlorprop)

MCPA

MCPP (mecoprop)Benzoic acids dicamba

Pyridine clopyralid

carboxylic acids fluroxypyrpicloramtriclopyraminopyralid

Quinoline quinclorac

carboxylic acids

Page 127: Table 1. Herbicide MOA classification system. HRAC WSSA group

clopyralid, acid picloram, acid

triclopyr, acid

Page 128: Table 1. Herbicide MOA classification system. HRAC WSSA group

Table 1. HRAC herbicide classification system.

HRAC WSSAgroup group Mode of action Chemical family Active ingredients

O 4 Act as Phenoxy- 2,4-D

synthetic carboxylic-acids 2,4-DB

auxins 2,4-DP (dichlorprop)

MCPA

MCPP (mecoprop)

Benzoic acids dicamba

Pyridine clopyralid

carboxylic acids fluroxypyrpicloramtriclopyr

Quinoline quinclorac

carboxylic acids

Page 129: Table 1. Herbicide MOA classification system. HRAC WSSA group

quinclorac

Page 130: Table 1. Herbicide MOA classification system. HRAC WSSA group

Table 1. HRAC herbicide classification system.

HRAC WSSAgroup group Mode of action Chemical family Active ingredients

P 19 Inhibition of Phthalamates naptalam

auxin trans-

port

Page 131: Table 1. Herbicide MOA classification system. HRAC WSSA group

Naptalam

1. Limited mobility in plants

2. Weakly bound to soil

3. Leaches readily

4. Average soil half-life of 14 days

5. Applied PRE to weeds

6. Controls selected broadleaf weeds

Page 132: Table 1. Herbicide MOA classification system. HRAC WSSA group

Table 1. HRAC herbicide classification system.

HRAC WSSAgroup group Mode of action Chemical family Active ingredients

Z 17 Unknown Organoarsenicals DSMA

MSMA

Page 133: Table 1. Herbicide MOA classification system. HRAC WSSA group

DSMA

MSMA

Page 134: Table 1. Herbicide MOA classification system. HRAC WSSA group

Organoarsenicals

1. Contain pentavalent As.

2. Pentavalent As is low toxicity to mammals, as

opposed to trivalent As in rat poison

3. Have no soil activity; bound tightly

4. Applied POST; limited apoplastic translocation;

act like contacts

5. Long soil persistence, but no carryover problems

because tightly bound to soil

6. Mode of action unknown.