Strategies for Pest Control

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Strategies for Pest Control
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Why Use Pest Control?

• Pests are responsible for nearly 1/3 of all
  pre-harvest crop losses

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Main Strategies for Pest Control

• Chemical
• Biological
• Integrated Pest Management
• Good Agronomic Practices
• Genetic Engineering

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History of Chemical Control (pesticides)

• 1000 B.C.? Fumigants (burning sulfur)
• 1200-1800s? plant extracts (pyrethrum, paris
  green)
• Early 1900s? compounds containing lead, arsenic,
  and sulfur
• 1930s ? DDT (nobel prize for perfect
  insecticide)
• 1950s? Beginning of large scale, pesticide
  spraying

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Costs of Pesticide Use

• Damaged water supplies
• Loss of fish and other organisms
• Healthcare from pesticide poisoning
• Regulation and monitoring
• Total cost of 4-10 billion/year

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Types of Pesticides

• Three main groups
• 1)Herbicides
• 2)Insecticides
• 3)Fungicides

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Herbicides

• Non-Selective
• kill everything (pre-emergence)
• i.e. Chlorate
• Selective
• kill certain species
• (post-emergence)
• i.e. atrazine-type herbicides

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How Do Herbicides Function?

• Inhibit electron flow in chloroplasts
• Inhibit biosynthesis of amino acids or prevent
  assimilation of ammonia
• Function as hormones to disrupt normal growth

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Problems With Herbicides

• Harmful to non-target species
• Some are not perfectly selective and damage the
  crop, leading to decreased yields

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Insecticides

• Chemicals used to kill insects, nematodes, and
  bacteria
• Function by inhibiting enzymes needed for life
  processes (i.e. organophosphates)

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Insecticides

• Many have high persistence and toxicity, thus
  have been banned (i.e. DDT)
• Current trend to find insecticides that are less
  persistent, but with higher target specificity

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Fungicides

• Usually applied as dusts to crops or coatings
  on seeds
• Must be on the plant before fungal spores attach
  and begin to grow

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Insecticide and FungicideIssues

• Resistance- over 500 sp. of insects have
  developed resistance to one or more insecticides
• Resurgence- pests rebound quickly
• Human Health Risks- 1,000 people/yr in U.S.
  report poisoning

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Biological Control

• Using natural
• predators, parasites
• and pathogens to control
• pest populations
• Usually non-native species
• Cassava mealybug in
• Sub-Saharan Africa
• Parasitic wasp introduced,
• very effective treatment

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Biological Control

• Bt corn- Kills butterfly and moth larvae
• Hormones- retain juvenile stage
• Pheromones- sex attractants used
  trapping/disorienting the pests
• Sterile mating partners- sterile insects produced
  in a lab and released into the environment to
  prevent reproduction
• Plant Immunization- non-virulent strains

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Problems With Biological Control

• Unknown ecological impact
• Introduced pest becomes a pest itself (cane toad
  in Australia)
• Bt Corn- non-target species harmed
• Expensive (i.e. millions of dollars to create
  enough sterile insects for release in the
  environment)

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Integrated Pest Management

• More sophisticated approach
• Using combination of pathogens, predators,
  parasites, weather, cultural practices, and
  resistant varieties
• Chemicals are a last resort
• More economically efficient and
  environmentally-friendly

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Integrated Pest Management

• Data is gathered in the field (age of plant, pest
  level, temperature, etc.)
• Determine type, extent and cost of intervention
• Compare the cost of intervention to the cost of
  the probable damages by pests
• Make a decision to treat or not

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Integrated Pest Management

• Can be effective
• Requires knowledge of population dynamics
• Difficult to determine pest levels, especially if
  its within the plant (i.e. viruses)

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Pest Control Good Agronomic Practices

• Crop rotation
• Hoeing
• Increasing crop plant density
• Manipulating planting and harvesting days

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Pest Control Genetic Engineering

• Can produce herbicide-tolerant plants
• Resistant to potato virus X
• Produces insect-resistant plants with Bt-toxin
  genes
• Produces plants resistant to fungi and bacteria

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Sources

• Chapter 13 Strategies for Pest Control
• Baird, C. and Michael Cann. Environmental
  Chemistry. 13th edition. 2005.