Plant disease & defences

• Plant diseases


  Caused by microorganisms including fungi, bacteria, viruses, and larger organisms like insects
• Deficiency diseases


  Caused by lack of essential minerals like nitrates or magnesium ions
• Nitrate deficiency


  • Stunted growth, not growing as much as they should
• Magnesium deficiency


  • Chlorosis (lack of chlorophyll), yellow leaves
• Symptoms of diseased plants

  • Abnormal growths or lumps
  • Malformed stems or leaves
  • Patches of decay
  • Spots of discoloration on leaves
• Diagnosing plant disease


  1. Take basic observations

  2. Match symptoms to a disease listed in a garden manual or website

  3. Send sample to plant pathologist for more detailed testing

  4. Trial and error (e.g. apply magnesium, spray with anti-fungal)
• Plant pathologist


  • Specializes in plant disease, can do detailed testing like microscopy, antigen detection, DNA tests
• Plant defenses


  • Physical (e.g. waxy cuticle, cell walls, bark)
  • Chemical (e.g. antimicrobial substances, poisons)
  • Mechanical (e.g. thorns, hairs, leaves that curl/droop)
• Many drugs are derived from plant chemicals, including aspirin from willow trees