table 1. herbicide moa classification system. hrac wssa group
Post on 12-Sep-2021
5 Views
Preview:
TRANSCRIPT
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)
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.
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
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.
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)
Flumiclorac-pentyl ester
Flumioxazin
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).
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)
oxadiazon
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)
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)
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.
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.
Uses of Sulfentrazone
2. Packaged mixtures
c. Surge
sulfentrazone + 2,4-D + MCPP + dicamba
POST control of broadleaf weeds in turf
PPO inhibitors
Lactofen, A. York, NCSU Acifluorfen, A. York, NCSU
Fomesafen, A. York, NCSU Flumiclorac, A. York, NCSU
Carfentrazone, A. York, NCSU
Carfentrazone, A. York, NCSU
Acifluorfen, A. York, NCSU
PPO inhibitors
Aim post-directed
A. York, NCSU
PPO inhibitors
Flumioxazin preemergence
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
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.
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
R1 R2
C
O
Ketone: a carbonyl carbon bonded to two
carbon atoms.
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
Clomazone -- Isoxazolidinone family
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.
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.
Culpepper, Univ. GA
Norflurazon carryover on cabbage
York, NCSU
Norflurazon
Clomazone
A. York, NCSU
Clomazone
+
phorate
Clomazone
+
aldicarb
Clomazone
A. York, NCSU
Clomazone drift
Mesotrione
A. York, NCSU
Mesotrione
A. York, NCSU
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
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.
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
HO -
O
C -
H
C -
H
H
N -
H
C -
H
O
P -
OH
OH
Glyphosate acid
Glyphosate Formulations
Glyphosate is formulated as one of three salts:
• diammonium salt (currently not on market)
• potassium salt
• isopropylamine salt
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
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
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
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.
Untreated
Clearout 41 Plus
Grower field, Clearout 41 Plus, 5 DAT
Glyphosate drift on non-RR corn
Glyphosate drift on non-RR corn
Glyphosate on non-RR corn; sprayer contamination
Glyphosate on non-RR corn; sprayer contamination
Glyphosate applied to non-RR corn
Glyphosate drift
Univ. Wisconsin
Univ. Wisconsin
Glyphosate drift
Double rate of glyphosate on RR soybean
Glyphosate sprayer contamination
N. Porter, UniroyalN. Porter, Uniroyal
Glyphosate on RR cotton
Glyphosate on RR cotton
Glyphosate on RR cotton
Glyphosate overtop RR cotton after 4-leaf stage
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
Glufosinate acid
Glufosinate-ammonium
Glufosinate Mode of Action
Inhibits enzyme glutamine synthetase.
NH3 accumulates, which is toxic.
Glutamic acid + glutamine
NH3
amino acids
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
Glufosinate
Univ. Wisconsin
A. York, NCSU
A. York, NCSU
Glufosinate
A. York, NCSU
A. York, NCSU
Univ. Wisconsin
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
H-N-H
NO2NO2
Basic structure of a dinitroaniline
Aniline ring with nitro group at 2- and 6-position of ring
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.
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.
Characteristics of Dinitroanilines
• Absorbed by roots of dicots, by
emerging coleoptile of grasses.
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.
Univ. Wisconsin
Root pruning with DNA’s
Root pruning
with DNA’s
Stunting by DNA herbicide
A. York, NCSU
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.
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
N
Pyridine
Pyridine herbicides consist of pyridine ring with various
substituent groups off the ring
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
pronamide
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
DCPA
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
Mode of Action
Acetamides
Chloroacetamides
Oxyacetamides
Seedling shoot growth
inhibitors. Impact several
processes in plants. Proposed
mechanism of action is
inhibition of VLCFAs.
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.
Metolachlor
O
C CH2 Cl
N
CH CH2 O CH3
CH3
*
*
Metolachlor has a chiral center and a chiral axis.
CH2 CH3
CH3
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
napropamide
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
Chloroacetamides
Chloroacetamides
Dewey Lee, UGA
Purdue Univ.
Chloroacetamides
Leafing out underground
A. York, NCSU
Chloroacetamides
Metolachlor preemergence
Chloroacetamides
A. York, NCSU
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
Cl Cl
C N
dichlobenil
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
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
R1 O
N - C - S - R3
R2
Basic structure of
a thiocarbamate
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
Thiocarbamates
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
bensulide
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
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
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.
O
O - (CH2)i - C - OH
Basic structure of a phenoxy-carboxylic acid
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.
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
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.
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
Univ. Wisconsin
2,4-D Postemergence
2,4-D
A. York, NCSU
Purdue Univ.
Univ. Wisconsin
Epinastic Response
to 2,4-D and 2,4-DB
A. York, NCSU
Soybean leaf distortion by 2,4-D
A. York, NCSU Purdue Univ.
Cotton leaf distortion by 2,4-D
A. York, NCSU
A. York, NCSU
2,4-D sprayer
contamination
on tobacco
A. York, NCSU
Malformed wheat heads
2,4-D
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
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
A. York, NCSU
Dicamba
Leaf cupping by dicamba
University of Missouri
Kansas State Univ.
A. York, NCSU
“Cobra-hood” caused by
dicamba or picloram
Univ. Missouri
dicamba
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
clopyralid, acid picloram, acid
triclopyr, acid
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
quinclorac
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
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
Table 1. HRAC herbicide classification system.
HRAC WSSAgroup group Mode of action Chemical family Active ingredients
Z 17 Unknown Organoarsenicals DSMA
MSMA
DSMA
MSMA
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.
top related