Cell Membrane Disruptors aka PPO Inhibitors

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Cell Membrane Disruptors(aka PPO Inhibitors)
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Cell Membrane Disruptors(aka PPO Inhibitors)

• Site of action
• Protoporphyrinogen Oxidase (PROTOX)
• Chemical families
• Diphenylethers
• N-phenylphthalimides
• Triazolinones
• Others

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Cell Membrane Disruptors

• Herbicides bind to Protoporphyrinogen oxidase IX
  and cause an accumulation of protoporphyrinogen
  IX.
• Protoporphyrinogen IX overflows the chloroplast
  and oxidizes to protoporphyrin IX.
• Protoporphyrin IX interacts with light and oxygen
  to generate singlet oxygen.
• Enzymes that normally prevent accumulation of
  protoporphyrin IX (Mg chelatase) are not
  available in cytoplasm.
• Singlet oxygen initiates lipid peroxidation which
  results in membrane damage, leakage of cell
  contents, disintegration of cell.

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Cell Membrane Disruptors

• Diphenylethers
• 1. Ex. lactofen (Phoenix/Cobra), soybean
• acifluorfen (Blazer), soybean
• fomesafen (Flexstar), soybean
• 2. Uptake foliar
• 3. Translocation little to none
• 4. MOA inhibit PROTOX
• 5. Controls broadleaves
• 6. Injury symptoms
• -leaves will have limp, water-soaked
  appearance
• -eventually necrotic speckling
• -tissue death
• 7. Characteristics
• -rapid activity
• -strongly adsorb to soil colloids, little
  potential to leach
• -light is required for activity

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Fomesafen
Acifluorfen
Lactofen
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Cell Membrane Disruptors

• Phenylphthalimide
• 1. Ex. flumiclorac (Resource) soybean,
  corn
• flumioxazin (Valor) soybean
• 2. Uptake soil uptake through root and shoot
  foliar uptake
• 3. Translocation some in xylem
• 4. MOA Inhibits Protox
• 5. Controls Annual broadleaf weeds
• 6. Injury symptoms - stunted plants
• - tan mottling
• - swollen soybean cotyledons
• 7. Characteristics - soil residual with some
  foliar activity
• - moderate soil persistence
• -soil activity is close to soil surface
• -incorporation reduces activity
• -light is required for activity

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Flumiclorac
Flumioxazin
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Cell Membrane Disruptors

• Triazolinones
• 1. Ex. sulfentrazone (Authority) soybean,
  tobacco
• carfentrazone (Aim) corn
• 2. Uptake soil uptake through root and shoot
  foliar uptake
• 3. Translocation some in xylem
• 4. MOA Inhibits Protox
• 5. Controls Annual broadleaf weeds and some
  grass
• 6. Injury symptoms - stunted plants
• - tan mottling
• - swollen soybean cotyledons
• 7. Characteristics - soil residual with some
  foliar activity
• - moderate soil persistence
• -soil activity is close to soil surface
• -incorporation reduces activity
• -light is required for activity

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Carfentrazone
Sulfentrazone
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Cell Membrane Disruptors

• General Characteristics
• 1. Can enter roots, stems, or leaves.
• 2. Light is required for activity.
• 3. Moderate to strong soil adsorption.
• 4. Herbicide action is near the soil surface
  for soil applied herbicides.
• 5. Soil incorporation greatly reduces activity
• 6. Fairly low mammalian toxicity (solvents in
  some products are caustic)

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Cell Membrane Disruptors

• Advantages of PPO Herbicides
• 1. Target site is well understood.
• 2. Get a very low use rate.
• 3. Large degree of chemical flexibility.
• 4. Fairly low mammalian toxicity.
• Disadvantages of PPO Herbicides
• 1. Chemistry is expensive.
• 2. Almost always have some degree of crop
  injury due to rapid activity before crop can
  metabolize to non-toxic form.