Turfgrass Herbicide Families & Mode-of-Action

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

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. 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

30. 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

31. “dormant” zoysiagrass

32. Green under “dormant” zoysiagrass

33. “Dormant zoysiagrass” spot sprayed with Roundup

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

35. 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

36. 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

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

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

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

41. 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

42. 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

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

44. 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

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

46. MSMA injury on tall fescue

47. Tee infested with Texas sedge

48. Texas sedge tee after treatment with MSMA

49. 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

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