Plant Diseases and Insect Pests

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Plant Diseases and Insect Pests

• Disease - any kind of injurious abnormality
• Physiological (environment)
• Other living organisms (pathogens)
• Pathogen - biological agent that causes the
  injury
• Insects
• Bacteria
• Fungi
• Viruses
• Nematodes
• Miscellaneous

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Plant Diseases and Insect Pests

• Parasite - an organism that derives nourishment
  from another living organism
• Host - an organism that provides nourishment to
  another
• Obligate parasite - organism that can only
  survive on the living host
• Host range - list of several different plants
  that some parasites can feed off of

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Plant Diseases and Insect Pests

• Bacteria - one-celled organisms that enter
  through wounds and cause rot
• Fungi - multi-celled organisms that either are
  saprophytes or parasites. Ex molds, mildew.
  Cause decay of plants

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Bacterial rot/wilt
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Fireblight on an apple
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Bacterial disease control?

• Start with clean pots potting media tools
• Start with clean seed or healthy transplants
• Use drip irrigation or water in the morning so
  the extra water on the surface of the leaves
  evaporates by evening
• Antibiotics now exist for injecting into trees
  but treatment is costly and the effects
  temporary. There are no antibiotic spray
  treatments.

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Fungal rots
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Fungus on foliage
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Fungal disease control?

• Start with clean pots potting media tools
• Start with clean seed or healthy transplants
• Use drip irrigation or water in the morning so
  the extra water on the surface of the leaves
  evaporates by evening
• Fungicides do exist. They can be used as a
  liquid drench, spray or powder.

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Captan Thiram synthetic fungicides
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Plant Diseases and Insect Pests

• Viruses - infectious particles made-up of nucleic
  acids (typically RNA in plants) with a protein
  coat. In the plant cell, the protein coat comes
  off and the RNA uses the plant cell to reproduce
  itself. These are obligate parasites.

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Virus
Tobacco Mosaic Virus
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No control methods!
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Plant Diseases and Insect Pests

• Nematodes - unsegmented worms that feed on roots
  and create wounds for bacteria and fungi to enter

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Nematode damage on tomato
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Nematode damage on tomato
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Nematode damage on carrot
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Foliar nematodes
Hosta
Zinnia
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How Plants are Damaged

• Damage by
• Direct feeding
• Secretion of toxic substances
• Secondary organism enters the wound
• Symptom - plants response to attack (wilt)
• Sign - structures produced by the attacking
  organism (webs, tunnels, etc.)

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Symptom wilt
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Webbing sign
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Spread of Insects and Disease

• Diseases and insects are spread to plants by
• Water
• Wind
• Insects
• Animals (including people) Ex TMV
• Machinery
• Plants are more susceptible to disease and insect
  attack when they are stressed (water or
  temperature)