1. Turfgrass Herbicide Families & Mode-of-Action
Tim R. Murphy
The University of Georgia

2. Herbicide Mode-of Action
Mode-of-Action - The entire sequence of
events that happen from the time the herbicide is absorbed to the eventual plant response (usually death).

3. Mode of Action Three phases Absorption Movement to target site
Inhibit biochemical reaction

4. Herbicide Mode-of-Action
The way a herbicide kills or inhibits the growth of susceptible plants!!

5. Why understand herbicide MOA?
Better understanding of how herbicides perform.
Diagnosing herbicide injury.
Professionalism.
Public relations.

6. Herbicide Classification
Selectivity
Herbicide movement in plants
Timing of application
Chemical Family
Mode of Action

7. Herbicide Classification - Selectivity
Selective
controls or suppresses one species of plant without seriously affecting the growth of another plant species.
Example
2,4-D will control many broadleaf weeds without seriously affecting turfgrasses.

8. Herbicide Classification - Selectivity
Nonselective
Nonselective herbicides control plants regardless of species.
Examples
Roundup Pro, Finale, Reward, Scythe

9. Xylem - nonliving tissue in a plant that transports water and mineral nutrients from the roots to the shoots.
Phloem - living tissue that transports sugars from the site of synthesis or storage to the site of use.

10. Translocated herbicides move.
Contact herbicides do not move in the plant
Phloem mobile herbicides move up and down in the plant
Xylem mobile herbicides move up in the plant
Translocated herbicides move.

11. Herbicide Movement in Plants
Contact
Rupture cell membranes.
Symptoms appear within hours.
Need complete coverage for kill.
Xylem Mobile
Taken up by primarily by roots.
Found in older leaves that are exporting sugars.
Do not move downward when foliar applied.
Phloem Mobile
Move to points of active growth or food storage.
Affect shoot tips, young buds and leaves.
Can cause contact burn.

12. Mode-of-Action Retention Absorption Translocation to active cell site
Inhibit biochemical reaction
Plant metabolism or breakdown

13. Plant leaf cuticle.

15. Plant Processes Affected by Turfgrass Herbicides
Photosynthesis
Amino acid and protein synthesis
Cell division
Cell membranes
Growth regulation
Growth inhibition
Fatty acid synthesis

16. Photosynthesis CO2 + H2O + Sunlight = C6H12O6 OR
Carbon dioxide + water + sunlight
will yield
Sugar

17. Triazines Atrazine – Aatrex, Simazine - Princep Metribuzin – Sencor
Used only on warm-season turfgrasses
Root and shoot absorbed (except simazine)
Inhibits photosynthesis, eventual membrane disruption, requires light
Pre and Post control

18. Photosynthetic inhibitors
Atrazine, simazine, Sencor
Light and active photosynthesis needed for activity
These herbicides interrupt energy flow resulting in free radicals
Free radicals react with cell membranes
Atrazine on bentgrass

19. Ethofumesate Prograss cool-season grasses and overseeded bermudagrass
primarily shoot absorbed, some by roots
not well absorbed after leaf cuticle is formed
translocated if root or shoot absorbed
appears to inhibit photosynthesis and respiration, not well understood

20. Bentazon Basagran T/O All warm- and cool-season turfgrasses
contact, foliage absorbed
limited translocation
can move in xylem if root absorbed
inhibits photosynthetic electron transport

21. Photosynthesis Inhibitors
Symptomology
Interveinal or veinal yellowing followed by death of plant tissue from leaf margins inward
POST applications cause rapid browning of plant tissue

22. Bladex
Cotoran
Source: W. K. Vencill, UGA

23. Amino acids Building blocks of plant proteins
Enzymes mediate biochemical reactions
Storage roles - seed reserves
Structural roles

24. Amino Acid Synthesis Inhibitors
Characteristics
Most of these herbicides have soil and foliar activity except glyphosate
Undergo significant translocation
Soil residual activity herbicide-dependent
Generally, low use-rate herbicides

25. Amino Acid Synthesis Inhibitors
Symptomology
Injury symptoms on grass include stunting, purple coloration, and inhibited root systems with “bottle-brush” appearance
Broadleaf plant symptomology includes formation of red or purple leaf veins, yellowing of new leaf tissue and blackening of terminal growth
Glyphosate injury includes initial yellowing followed by death of affected tissue

26. Imidazolinones Image, Plateau warm-season grasses, except bahiagrass
rapid shoot and root absorption
translocates to meristematic areas
inhibits leucine, isoleucine and valine synthesis
growth is impaired and plants die over 1 to 3 wk period

27. Image on bermuda

28. Sulfonylureas
Manor, Corsair, SedgeHammer,TranXit, Monument, Revolver, Certainty
rapid shoot and root absorption
translocates to meristematic areas
inhibits leucine, isoleucine and valine synthesis
growth is impaired and plants die over 1 to 3 wk period

29. Sulfonylureas
Manor, Blade – warm-season grasses, except bahiagrass; also on Ky. Bluegrass
Corsair – Ky. Bluegrass, bahiagrass, bermudagrass
SedgeHammer– all warm- and cool-season turfgrasses
Revolver – bermuda, ‘Meyer’ zoysia
Monument – bermuda, zoysia
TranXit – bermuda, zoysia, centipede, overseeded bermudagrass
Certainty – bermuda, zoysia, centipede, St. Augustine

30. Pyrimidunyloxybenzoic
Velocity
Overseeded bermudagrass
rapid shoot and root absorption
Translocated via phloem
inhibits leucine, isoleucine and valine synthesis
growth is impaired and plants die over 2 to 3 wk period

31. Glyphosate
Isopropylamine salt - Roundup Pro , GlyphoMate 41, Razor Pro, Prosecutor
Ammonium salt - Roundup ProDry
Diammonium salt - TouchDown Pro
foliage absorbed
extensively translocated in phloem
inhibits tryptophan, tyrosine and phenylalanine synthesis
growth is impaired and plants die over 1 to 3 wk period

32. “dormant” zoysiagrass

33. Green under “dormant” zoysiagrass

34. “Dormant zoysiagrass” spot sprayed with Roundup

35. Cell Division
Plant growth is due to cell division and cell elongation.

36. Dinitroanilines Benefin - Balan Oryzalin - Surflan
Pendimethalin - Pendulum
Prodiamine - Barricade
Trifluralin - Treflan
Shoot and root absorbed, no translocation
Inhibit cell division (tubulin formation)
Used on most warm- and cool-season turfgrasses

37. Dithiopyr Dimension MOA is similar to dinitroanilines
Shoot and root absorbed, no translocation
Inhibit cell division (tubulin formation)
Has POST activity on seedling crabgrass
Used on most warm- and cool-season turfgrasses

38. DNA Root inhibition Swollen, club shaped roots
Surflan on St. Augustinegrass
pendimethalin on zoysiagrass
Dimension on bermudagrass
Swollen, club shaped roots

40. Asulam Asulox readily absorbed by foliage, minor root absorption
translocates in phloem and xylem
inhibits cell division
also inhibits RNA and protein synthesis
used on St. Augustinegrass and ‘Tifway’ bermudagrass

41. Pronamide Kerb root absorbed, translocated in xylem
controls emerged cool-season grasses
inhibits cell division
Used only on warm-season turfgrasses

42. Cell Membranes
Contain the cellular contents and regulate the entry and exit of substances that promote or inhibit plant metabolism

43. Diquat Reward LS contact, very rapidly absorbed,does not translocate
requires light for activity
disrupts electron flow in photosynthesis
leads to formation of free radicals which damages cell membranes
cellular fluids leak, followed by death
used on dormant bermudagrass

44. Glufosinate Finale readily absorbed by leaves
primarily contact activity, limited translocation
inhibits key enzyme involved in conversion of ammonia into amino acids
toxic levels of ammonia build up, causes cell membrane disruption, interferes with photosynthesis
used on dormant bermudagrass

45. Cell Membrane Disrupters
Finale, Reward, Paraquat
Finale on zoysia
Damage occurs within hours.
Membrane destruction.
No redistribution
Complete coverage for kill.

46. Organic Arsenicals MSMA, DSMA, CMA, CAMA foliage absorbed
Mobile in xylem and phloem
Not well understood, rapid desiccation indicates cell membrane destruction
Used on cool-season grasses, bermuda and zoysiagrass

47. Leaf burn on broadleaves and grasses with yellow leaf tips on grasses
Terminal yellowing of grasses
MSMA on zoysia

48. MSMA injury on tall fescue

49. Tee infested with Texas sedge

50. Texas sedge tee after treatment with MSMA

51. Oxadiazon Ronstar all turfgrasses, except centipede
readily shoot absorbed, less so by roots
can be foliage absorbed, “contact burn”
does not significantly translocate
Light required
inhibits key enzyme in chlorophyll synthesis, toxic radicals formed, disrupts cell membranes

52. Oxadiazon (Ronstar) PRE
2G – Ky. Bluegrass, Bermuda, seashore paspalum, t. fescue, zoysia, St. Augustine
50WSP – bermuda, St. Augustine, zoysia
Annual grasses, selected broadleaves

53. Ronstar 2G and 50WSP - At Sprigging
Apply immediately before or after sprigging bermudagrass and zoysiagrass
Pre-sprigging (1 day before sprigging slightly safer than post-sprigging)
Irrigate ASAP for best results

54. Carfentrazone QuickSilver Contact, quickly absorbed Fast-acting
Inhibits enzyme (protoporphyrinogen oxidase) in chlorophyll synthesis pathway. Leads to formation of toxic intermediates which disrupt cell membranes.

55. Carfentrazone
Sold with phenoxy herbicides and dicamba as PowerZone and SpeedZone
All turfgrasses
does not significantly translocate

56. Sulfentrazone Dismiss Root and shoot absorbed Fast-acting
Inhibits enzyme (protoporphyrinogen oxidase) in chlorophyll synthesis pathway. Leads to formation of toxic intermediates which disrupt cell membranes.

57. Carfentrazone and Sulfentrazone
Carfentrazone – POST, all turfgrassses
Sulfentrazone – PRE, although does have POST activity

58. Growth Regulation
Naturally produced hormones (auxins, cytokinins, gibberellins, others) are involved in the regulation of normal growth and development.

59. Growth Regulator Herbicides
These herbicides affect several plant processes such as cell division, cell enlargement, protein synthesis and respiration. They act by upsetting the normal hormonal balance in plants.

60. Growth Regulator Herbicides
Phenoxys
2,4-D, dichlorprop
mecoprop, MCPA
Benzoics
Banvel, Vanquish
Picolinic Acids
Confront
Turflon
Lontrel
SpotLight
Quinolinecarboxylic
Drive
Trimec on bermuda

61. Phenoxy, Benzoic Acid, Picolinic Acid
readily absorbed by foliage, less so by roots
extensively translocated
interfere with DNA, RNA and protein synthesis
results in uncontrolled cell division and elongation
vascular tissues are plugged, 1 to 3 wks

62. Quinclorac Drive shoot and root absorbed
readily translocates in xylem and phloem
MOA not fully understood
Broadleaf's - alters auxin levels
Grasses - affects cell wall synthesis, increases cyanide and ethylene production
Used on tall fescue, zoysia and bermudagrass, Ky bluegrass

63. Drive on crabgrass, 7 days after treatment

64. Phenoxy, Benzoic Acid, Picolinic Acid
Phenoxies – used on cool- and warm season turfgrasses, except St. Augustine
Benzoic acids - used on cool- and warm season turfgrasses
Lontrel – all cool- and warm-season grasses
Confront – cool- and warm-season grasses, except St. Augustine
Turflon – Ky. Bluegrass and tall fescue

65. Growth Regulator Herbicides
Symptomology
Broadleaf plant stem twisting and curling
Leaves on broadleaf plants exhibit cupping, crinkling, strapping, or drawstring affect
Symptoms on grass plants include leaf rolling, crinkling, brace root fusion and malformation.

66. 2,4-D overdose on St. Augustinegrass

67. 2,4-D Injury on Soybean

68. Growth Inhibition Exact MOA not known Inhibit root and shoot growth
Disrupt cell division, cell enlargement
Also may disrupt lipid synthesis, nucleic acid and protein synthesis

69. Growth Inhibitors Bensulide - Betasan, Pre-San Metolachor - Pennant
root absorbed, essentially no translocation
disrupts cell division and enlargement
Metolachor - Pennant
mainly shoot absorbed, some root uptake
translocates in xylem
inhibit root and shoot growth
disrupts protein, fatty acid and lipid synthesis

70. Growth Inhibitors Bensulide - Betasan, Pre-San Metolachor – Pennant
Cool- and warm-season turfgrasses
Metolachor – Pennant
Only on warm-season turfgrasses

71. Growth Inhibitors Siduron - Tupersan
readily absorbed by roots, translocated in xylem
inhibits root growth, may disrupt mitosis
Used only on cool-season turfgrasses and zoysiagrass

72. Growth Inhibitors Gallery
rapidly absorbed by roots, minimal foliage absorption
moves in xylem
inhibits cell wall biosynthesis
Used on all cool- and warm-season turfgrasses

73. Fatty Acid Synthesis
Fatty acids are important components of cell membranes
Inhibition fatty acid synthesis blocks production of lipids needed for new cell growth.

74. Fatty Acid Inhibitors Cyclohexanediones
sethoxydim - Vantage, Poast
used only on centipedegrass and fine fescue
clethodim – Envoy
used only on centipedegrass
Rapidly absorbed by leaves, extensively translocated via phloem to meristems
Inhibit key enzyme in fatty acid synthesis

75. Fatty Acid Inhibitors Aryl-oxy-phenoxies
fenoxaprop - Acclaim Extra
fluazifop - Fusilade II
diclofop - Illoxan
Rapidly absorbed by leaves, extensively translocated via phloem to meristems, (diclofop translocation is slow)
Inhibit key enzyme in fatty acid synthesis

76. Fatty Acid Inhibitors Aryl-oxy-phenoxies fenoxaprop - Acclaim Extra
used on cool-season grasses and zoysiagrass
fluazifop - Fusilade II
Used only on tall fescue and bermudagrass
diclofop – Illoxan
Used only on bermudagrass

77. Fatty Acid Synthesis Inhibitors - Grass Herbicides
Reddening of leaf tissue.
Discoloration of tissue at and above the nodes.
Tissue and leaves in the leaf whorl can easily be separated from the rest of the plant.
No broadleaf activity.
Fusilade on dallisgrass

78. Fatty Acid Synthesis Inhibitors
Initial injury in meristematic regions occurs where newest leaves are developing
These regions will turn chlorotic, which is followed by necrosis
The affected area will become “rotted” and will easily separate from rest of plant
Injury will develop slowly (7 to 14 days)

79. “rotted” meristem
Source: W. K. Vencill, UGA

80. Turf
Weed
Management
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