Grade 9 Science

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Pests Pesticides

• Grade 9 Science
• Ms. Brothers

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Pests

• There are no pests in nature it is all
  subjective
• Organisms that might compete or damage crop
  species (reduce yield)
• Weeds, mosquitoes, mice

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Monocultures

• When farmers plant a monoculture, they create the
  ideal environment for pests
• Colorado potato beetles

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Pesticides

• A substance (poison) to kill pests
• Herbicides ? plants
• Insecticides ? insects
• Rodenticides ? rodents (mice)
• Fungicides ? fungus
• Molluscicides ? snails
• Piscicides ? fish

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Pesticides

• 1. Long-lived lasts many years
• E.g. synthetic pesticides
• 2. Short-lived lasts a few days
• E.g. Natural pesticides

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Pesticides

• 3. Broad-spectrum toxic to wide range of species
• E.g. DDT Insecticide toxic to MOST insect
  species
• 4. Narrow-spectrum toxic to a limited of
  species
• E.g. Bt (Bacillus thuringiensis) Insecticide
  toxic to only caterpillars, beetle larvae, fly
  larvae

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How do they work?

• Physical harm
• E.g. diatomaceous earth abrasive powder
  scratches outer coating of small organisms

• Chemical harm
• E.g. interfere with photosynthesis damage vital
  organs, etc.

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How do they work?

• Direct
• Delivered by contact pest must touch pesticide
• Indirect
• e.g. herbicide that is sprayed on the grass will
  only take effect once it is taken up by the roots
  of the weed.

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Issues with Pesticides

• Non-target species
• Broad-spectrum pesticides will kill species that
  were not intended to be killed
• Might even kill potentially beneficial organisms,
  i.e. Predatory insects that normally feed on
  pests
• Thereby causing farmers to be more dependent on
  pesticides

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Non-target species

• Other examples
• Honeybees killed ? unable to pollinate fruit
  crops
• DDT to kill mosquitoes (reduced spread of
  malaria), but also killed wasps. The wasps ate
  thatch-eating caterpillars, and since their
  predator was killed, they ate the villagers
  thatch roofs.

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Issues with Pesticides

• Bioamplification
• The concentration of pesticide that accumulates
  in the body of an organism
• Pesticides that bioaccumulate do so because they
  cannot easily be excreted from the body.
• If a pesticide bioamplifies in a food chain, it
  may reach toxic concentrations
• E.g. DDT, mercury, PCBs

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Issues with Pesticides

• Pesticide resistance
• When pesticides are used for long periods of
  time, it might lose its ability to control the
  pest.
• Individuals will survive an application of
  pesticide, and will reproduce and pass on their
  resistance to their offspring
• After many generations, the population can become
  highly resistant to a particular pesticide

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Issues with Pesticides

• Pesticide resistance continued...
• Global scale pesticide resistance is a serious
  concern

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Organic farming

• Farming without the use of synthetic pesticides
  or fertilizers
• Accept crop losses ? Higher prices for products
• Control
• Biological
• Altered timing
• Crop rotation mixed planting
• Baiting pest

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Integrated Pest Management

• We can reduce our dependence on pesticides by
  using organic farming in combination with other
  types of management methods
• The goal
• To maximize efficiency
• Keep costs low
• Reduce harm to the environment