A Closer Look at Herbicides: Why they kill plants and not you

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A Closer Look at Herbicides Why they kill
plants and not you

• Brett W. Bultemeier
• William Haller
• Jay Ferrell
• Greg MacDonald
• University of Florida, IFAS
• Center for Aquatic and Invasive Plants
• http//plants.ifas.ufl.edu

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Why do herbicides kill plants?

• They inhibit a process in the plant that is
  essential to life.

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Plant processes inhibited by herbicides

• photosynthesis
• amino acids and proteins
• fatty acid synthesis
• growth inhibition
• cell membranes
• pigment synthesis
• growth regulation

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Photosynthesis Inhibition

• Diquat, Atrazine etc.
• Contact herbicide
• Herbicidal effect Rapid

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2. Amino acids inhibitors

• essential building blocks for plant growth and
  function
• unlike animals, plants make their own
• amino acids are the primary components of
  proteins and nucleic acids

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How do they work?

• Block a specific enzyme

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Why is glyphosate not harmful to humans?

• There is no EPSP enzyme in our bodies
• The herbicide has nowhere to bind
• It flushes out in urine

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Growth Regulators 2,4-D, Garlon, etc

• Mode of action Hormone mimics
• Systemic
• Herbicidal effect Rapid

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How do they work?

• hormones control plant growth and developmental
  changes, always present
• These herbicides are very similar to these growth
  hormones
• They overload the plant with hormone
• The plant grows itself to death

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2,4-D
Cucumber
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Bleaching herbicides fluridone

• Blocks synthesis of carotenoids
• These compound protect chlorophyll
• Causes the plant to turn white
• Chlorophyll gets too much sun and cant produce
  energy
• Plant starves to death

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Why do herbicides kill plants but not people?

• They inhibit a process in the plant that is
  essential to life
• Many inhibited processes do not occur in humans
• Exposure to humans is limited
• Put out at ppm or ppb

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PPB
-fluridone 5-10 ppb -only 5-10 people in all of
China are herbicide
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Glyphosate toxicity

• Advil 8 tablets 20 mg/kg
• Tylenol 8 tablets 50 mg/kg

The smaller the number, the greater the toxicity
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Acute Toxicity (LD50 mg/kg)
Fluridone gt 10,000 Glyphosate gt
5,000 2,4-D 1,000 Diquat
600 Endothall (191) 575 Copper
470 Endothall (K) 280
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Acute Toxicity (LD50 mg/kg)

• Endothall at 280 mg/kg
• 80 kg person (180 lbs) needs 22,400 mg
• Endothall treated at 11mg per gallon of water
• Would need to drink 2,036 gallons
• Death by water!!!

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Dont herbicides stay around forever?

• Many herbicides in aquatics breakdown rapidly
• Half-life a few days
• Longest lasting aquatic half-life 1 month

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Silent Spring

• Rachel Carson 1962
• In response to unrestricted irresponsible actions
• At the time she was ABSOLUTELY correct

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Silent Spring Concerns

• Persistent chlorinated hydrocarbons
• Large scale applications
• Unknown effects to food chains
• Untrained applicators

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Silent Spring Concerns

• Persistent chlorinated hydrocarbons
• Large scale applications
• Unknown effects to food chains
• Untrained applicators

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Agent Orange Syndrome

• Agent orange was a mix of 2,4-D and 2,4,5-T
• By themselves not a problem
• Cheap manufacture had contaminate of dioxin and
  was concentrated

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Solutions

• EPA formed 1970
• FIFRA amended 1974
• Burden of safety on industry
• No harm to humans, wildlife, crops, livestock or
  the environment

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Risks/Benefits of herbicides

• Herbicides do have some risk associated
• EPA analyzes risks and puts measures in place to
  limit risks
• Any compound with too much risk is not registered
• Humans assume risk on a regular basis
• Driving
• Medicines
• Exposure to sun
• Cleaning products etc

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Risks/Benefits of herbicides

• Herbicides have major benefits
• Efficient and effective
• Very selective
• Many times the only solution
• Benefits of herbicides must and do outweigh the
  risks
• EPA very conservative, must have huge swing to
  benefit side
• Margin of safety very large

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Summary

• Herbicides kill the plants in a very plant
  specific manner
• Humans are not plants
• Herbicides are used at very low rates
• EPA and environmental awareness serve as a check
  on herbicides
• Herbicides do have some risk
• Humans analyze and assume risk everyday
• Herbicides also have a big benefit
• Often the only effective and efficient means for
  control

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Thank You!!!
GO GATORS!!!
plants.ifas.ufl.edu