1. Top 3 Modes of Action
    • better understanding of how herbicides perform
    • improve herbicide performance
    • Diagnose herbicide injury
  2. 6 Plant Processes and Functions
    • photosynthesis (food)
    • pigments (energy/light capture)
    • respiration (energy)
    • amino acids (protein/growth)
    • lipids (cell membranes)
    • mitosis (cell division)
  3. Why do we use herbicides?
    • Reduce impact of invasive species
    • secure the presence of targeted species
  4. Two classes of herbicides
    • Selective-controls one species of plant without affecting the growth of another species (2 4-D)
    • Nonselective- controls plants regardless of species (Roundup)
  5. Sites of Absorptions and Translocation
    • foliar contact
    • root contact
    • xylem
    • xylem & phloem
    • phloem
  6. What is Mode of Action?
    sequence of events from absorption of the herbicide into the plant until the plant dies
  7. 2 most common modes of action
    • plant growth regulators
    • amino acid biosynthesis inhibitors
  8. 2nd most common modes of action
    • photosynthesis inhibitors
    • cell membrane disrupters
  9. plant growth regulators
    • synthetic auxins (regulate plant growth)
    • affect several plant processes like cell division, cell enlargement, protein synthesis and respiration
    • act by upsetting the normal hormonal blance in plants
  10. herbicide uptake in plant growth regulators
    • foliar contact
    • root contact
    • translocated in both xylem & phloem
  11. plant growth regulators selectively kill
    • broadleaf plants
    • injury may occur in grasses
    • (2 4-D)
  12. plant growth regulators symptoms
    • on newly developed leaves
    • abnormal growth causing twisting stems
    • stems swell cuz of rapid cell division
    • leaves exhibit cupping, crinkling, strapping or drawstring affect
    • symptoms on grasses include leaf rolling, crinkling, brace root fusion and malformation
    • flower sterillity and missing grain in crops
  13. plant growth regulators concerns
    • herbicide resistance
    • drift and injury to nontarget plants
    • groundwater contamination
  14. amino acid biosynthesis inhibitors
    • prevent synthesis of certain amino acids produced by plants
    • excellent foliar and root absorption
    • broad weed spectrum
    • translocates to shoot and root new growth in both xylem and phloem
    • (Roundup)
    • plants stop growing shortly after application
    • plant death may be slow (10+ days)
  15. Symptoms of amino acid biosynthesis inhibitors
    • chlorosis of leaves (turn yellow)
    • stunted growth
  16. important category of amino acid biosynthesis inhibitors
    EPSP inhibitors
  17. glyphosphate
    • tightly absorbed and inactive in soil
    • phloem translocated
    • inhibits EPSP enzyme responsible for production of aromatic amino acids
    • very nontoxic
  18. photosynthesis inhibitors
    • control annual or perennial grasses or broadleaves
    • shut down the photosynthesis process
    • slow starvation of the plant
    • plant experiences more rapid death due to production of secondary toxic substances
    • injury symptoms: yellowing of leaf tissue followed by death of the tissue
    • (Spike 20P)
  19. photosynthesis inhibitors symptoms
    • occur after coteyledons and first leaves emerge (Dont prevent seedlings from germinating or emerging)
    • yellowing (chlorosis) of leaf tissue followed by death (necrosis) of tissue
    • older and larger leaves affected first
  20. cell membrane disruptors
    • postemergence contact herbicides
    • little soil activity
    • activated by exposure to sunlight to form oxygen compounds such as hydrogen peroxide
    • oxygen compounds destroy plant tissue by rupturing plant cell membranes
    • perennial weeds usually regrow cuz there is no herbicide movement to underground root or shoot systems
    • controls weeds in 24-48 hours
    • broad-spectrum and non-selective control of grasses, broadleaf weeds and sedges
    • no residual effect
    • gramoxone max
  21. symptoms of cell membrane disruptors
    rapid necrosis (cell death)
  22. herbicide resistance is not due to
    • sprayer skips or plugged nozzles
    • weather problems that cause poor control
    • plants that are naturally tolerant to herbicide
    • genetic changes caused by herbicide
  23. herbicide resistance
    the ability of a plant to survive and reproduce after treatment with a dose of herbicide that would normally kill a plant
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