1. Herbicide Classification by Mode of Action
• Inhibit photosynthetic electron transport
• Inhibit amino acid biosynthesis
• Inhibit protoporphyrinogen oxidase
• Inhibit lipid biosynthesis (ACCase inhibitors)
• Act as growth regulators
• Inhibit carotenoid biosynthesis
• Inhibit seeding growth

2. Inhibit photosynthetic electron
transport
Herbicide Common Trade
Family Name Name
Triazines atrazine AAtrex
ametryn Evik
simazine Princep
cyanazine Bladex
metribuzin Sencor,Lexone
hexazinone Velpar
atrazine + cyanazine Extrazine II

3. Triazines
• Stop photosynthesis: you see yellowing
• Mobile in plant and environment (move on
soil off site)
• pH—low pH are soil bound (unavailable),
high pH are available for plant uptake
• Low pH, lime increases pH, used high
atrazine on corn, then plant small grains get
injury

4. Inhibit photosynthetic electron
transport
Herbicide Common Trade
Family Name Name
Phenylureas linuron Lorox
tebuthiuron Spike
diuron Karmex
siduron Tuperson
fluormeturon Cotoran

5. Phenylureas
• Mobile in plant

6. Inhibit photosynthetic electron
transport
Herbicide Common Trade
Family Name Name
Uracils bromacil Hyvar
terbacil Sinbar

7. Uracils
• Mobil in plant
• Symptoms
– Bleaching and yellowing

8. Inhibit photosynthetic electron
transport
Herbicide Common Trade
Family Name Name
Diazinones bentazon Basagran
pyridate Tough
chloridazon Pyramin

9. Diazinones
• Do not move in plant—contact activity

10. Inhibit photosynthetic electron
transport
Herbicide Common Trade
Family Name Name
Bipyridyliums paraquat Gramoxone
Extra
diquat Diquat

11. Bipyridyliums
• Do not move in plant—contact activity

12. Inhibit photosynthetic electron
transport
Herbicide Common Trade
Family Name Name
Benzonitriles bromoxynil Buctril

13. Benzonitriles
• Does not move in plant

14. Inhibit amino acid biosynthesis
(ALS)—Imi’s
Herbicide Common Trade
Family Name Name
Imidazolinones imazethapyr Pursuit
imazaquin Scepter
imazapyr Arsenal
imazamethabenz Assert
imazamox Raptor
imazapyr+ imazethapyr Lightning

15. Imidazolinones (Imi’s)
• ALS: block an enzyme so the plant cannot make
certain amino acids
• Scepter/Imi’s need rain to activate—in a dry year
there is carryover to the next crop
• long lived in environment
• Symptoms:
– prunes roots
– purpling and stunted plant
– bright yellow areas in whorl of plant

16. Inhibit amino acid biosynthesis
(ALS)—SU’s
Herbicide Common Trade
Family Name Name
Sulfonylureas bensulfuron Londax
chlorimuron Classic
chlorsulfuron Glean, Telar
metsulfuron Ally
nicosulfuron Accent
primisulfuron Beacon
sufometuron Oust

17. Sulfonylureas (SU’s)
• ALS: block an enzyme so the plant cannot make
certain amino acids
• Soilborne
• Symptoms:
– Pruned roots
– Short plant
– Yellowing in whorl
• Permit—in very warm temperature, actively
growing corn has a tough time growing = late
season “buggy whipping”

18. Sulfonylureas (SU’s) cont.
• Lime amended slug = high pH = SU
carryover
• Low to normal pH (<6.0-6.5) = microbes
work to break down hericide = no carryover
= good
• High pH (>6.5) slows microbial activity and
hydrolysis stops = Bad!

19. Inhibit amino acid biosynthesis
(ALS)—SU’s
Herbicide Common Trade
Family Name Name
Sulfonylureas thifensulfuron Harmony GT
triasulfuron Amber
tribenuron Express
thifensulfuron Harmony
+ tribenuron Extra
Halosulfuron Permit,Battalion
rimsulfuron Matrix
prosulfuron Peak

20. Inhibit amino acid biosynthesis
(ALS)—SU’s
Herbicide Common Trade
Family Name Name
Sulfonylureas primisulfuron+
prosulfuron Exceed,Spirit
rimsulfuron +
thifensulfuron Basis
sulfosulfuron Maverick

21. Inhibit amino acid biosynthesis
(ALS)
Herbicide Common Trade
Family Name Name
Sulfonamides flumetsulam Python

22. Sulfonamides
• ALS: block an enzyme so the plant cannot
make certain amino acids
• Cold, wet damage is worse because plant is
not actively growing—does not metabolize
herbicide
• Symptoms:
– Purpling
– stunting

23. Inhibit amino acid biosynthesis
Herbicide Common Trade
Family Name Name
Phosphono glyphosate Roundup,
Amino Acid Touchdown
Derivatives

24. Phosphono amino acid
derivatives
• Roundup blocks an emzyme—not a
photosynthesis inhibitor
• Symptoms:
– Yellow band where spray droplet landed (stays
yellow all season)
– Will kill Non-Roundup Ready Corn

25. Inhibit protporphyringen oxidase
(PPO’S)
Herbicide Common Trade
Family Name Name
Diphenyl ethers acifluorofen Blazer
lactofen Cobra
fomesafen Reflex
oxyfluorofen Goal
Oxadiazoles sulfentrazone Authority

26. PPO’s
• Another enzyme system is blocked
• Symptoms:
– Bronzing (contact burn)

27. Inhibit lipid biosynthesis (ACCase
Inhibitors)
Herbicide Common Trade
Family Name Name
Aryloxyphenoxy- diclofop Hoelon
Propionates fluazifop Fusilade DX
(ACC-fop) fenoxaprop OptionII,Acclaim
quizalofop Assure II
fluazifop + Fusion
fenoxaprop
Cyclohexanediones sethoxydim Poast, Poast Plus
(Acc-dim) clethodim Select

28. ACCase Inhibitors
• Works on enzyem system—goes to
meristem and kills it
• Post grass products in soybeans

29. Act as growth regulators
Herbicide Common Trade
Family Name Name
Phenoxys 2, 4-D Many
MCPP Many
MCPA Many
2, 4-D B Butyrac,
Butoxone
Benzoic acids dicamba Banvel,
Clarity,
Distinct

30. Growth Regulators: Oldest compounds
• Symptoms:
– Distortion in plant growth
– Bending of corn, twisting of leaves
– Fusion of brace roots
– If applied too late, kills ear—no kernals, can stop the
development of seed head in small grains
– Cupping in leaves upward (2, 4D)
– Cupping in leaves downward (dicamba) = “Cobra
Head”

31. Act as a growth regulator
Herbicide Common Trade
Family Name Name
Pyridines picloram Tordon
clopyralid Stinger
triclopyr Garlon

32. Inhibit carotenoid biosynthesis
(Pigment inhibitors)
Herbicide Common Trade
Family Name Name
Isoxazolidinones clomazone Command
Pyridazinones norflurazon Zorial,
Solicam
Isoxazoles isoxaflutole Balance

33. Pigment inhibitors
• Symptoms:
– Bleach leaves—turn white
– Carryover in small grains with Command—
white plants

34. Inhibit seedling growth (Shoot
inhibitors)
Herbicide Common Trade
Family Name Name
Chloroacetamides metolachlor Dual
alachlor lasso,
Micro-Tech
propachlor Ramrod
acetachlor Harness,
Surpass
dimethenamid Frontier

35. Shoot inhibitors (Chloroacetamides)
• Main group outside of permit
• Symptoms:
– Typical “buggy whipping” early in season
– Puckering on soybeans with Dual, Lasso,
Frontier
• V-shape at puckering at leaf tip
• Favored by cold, wet conditions

36. Inhibit seedling growth (Shoot
inhibitors)
Herbicide Common Trade
Family Name Name
Thiocarbamates EPTC Eptam
EPTC + safener Eradicane
butylate+safener Sutan Plus

37. Shoot inhibitors (Thiocarbamates)
• Incorporated products
• Thio=sulfur
• Symptoms:
– “buggy whipping” early in season
– Puckering on soybeans

38. Inhibit seedling growth (Root
inhibitors – DNA’s)
Herbicide Common Trade
Family Name Name
Dinitroanalines trifluralin Treflan, etc
ethafluralin Sonalan
penimethanlin Prowl
benefin Balan
oryzalin Surflan

39. Root inhibitors (Dinitroanalines)
• Important group
• Proves brittle bean syndrome
• Symptoms:
– Pruned roots, stubby