Plant Pathology

Course CodeBHT206
Fee CodeS2
Duration (approx)100 hours
QualificationStatement of Attainment

Garden School -Distance Learning Course

Plant production is reduced significantly every year, due to pathological problems. To control these problems is to increase productivity, and for the horticultural business that means increased profit margins.

PLANT PATHOLOGY IS NOT simply a study of pests  and diseases. Some pests are in fact not pathological problems, and there are pathological problems which are not pests or diseases.

PLANT PATHOLOGY is about problems in plants caused by physiological damage or irritation at a cellular level. It is concerned with problems which affect parts of the plant cell, leading to malfunctions in the normal processes which occur within the plant.



Lesson Structure

There are 8 lessons in this course:

  1. Introduction
    • Overview of plant disease
    • Diagnosis of problems: nutritional, environmental, pathological
    • Symptoms
    • Common terminology
  2. Types of Diseases
    • Morphological changes
    • Necroses
    • Hypoplases
    • Hyperplases
    • Types of pathogens: viruses, bacteria, actinomycetes, fungi, nematodes
    • Techniques for diagnosing plant diseases: optical equipment, preparing pathogens for observation, culture methods, inoculation, etc
    • Plant viruses; detection and diagnosis
    • Plant nematodes
    • Case study: Australian plant nematodes
    • Main types of diseases
    • Spots
    • Rots
    • Cankers
    • Galls
    • Mildews
    • Rusts
    • Moulds
    • Wilts
    • Scabs
    • Others
    • Using a key to diagnose diseases in plants
  3. The Lifecycle of a Disease
    • Inoculation
    • Penetration
    • Infection
    • Growth and reproduction
    • Dissemination
    • Methods of penetration by bacteria and nematodes
    • Lifecycle of nematodes
    • Fungal biology
    • Role of insect spreading fungal and bacterial pathogens
  4. Control Techniques
    • Sanitation
    • Resistant Plant Varieties
    • Biological Controls
    • Soil Drenches/dips
    • Chemical Controls
    • Nematicides
    • Soil fumigants
    • Contact poisons
    • Fungicides and the environment
    • Systemic fungicides
    • Misters, dusters, blowers, sprayersSpray maintenance and cleaning
    • Natural controls: cultural, physical, biological, etc
    • Terminology
  5. Selected Pathogen Diseases Ornamentals
    • Fungi affecting turf
    • Phytopthera cinnamomi
    • The process of tree decay: Shigo
    • Case study: how phytopthera cinnamomi kills a susceptible Eucalyptus
    • Peach powdery mildew
    • Rose powdery mildew
    • Honey fungus on rhododendrons and azaleas
    • Petal blight on rhododendrons and azaleas
  6. Selected Pathogen Diseases Crops
    • Sclerotinia rot in vegetables
    • Nematodes and citrus production
    • Citrus diseases: scaly butt, lemon crinkle, citrus canker
    • Brown rot
    • Fire blight
    • Apple fruit rot caused by trichoderma harzianum
    • Prunus necrotic ringspot virus in cut flower roses
    • Potato and tomato blight
    • Club root
  7. Non-Infectious Diseases
    • Nutritional disorders
    • Lack of water
    • Excess water
    • Other environmental problems
    • Disorders caused by man: mechanical damage, pollution
    • Case Study: Air pollution
    • Other disorders: genetic, disturbed growth
    • Non parasitic turf problems
  8. Special Project

Each lesson culminates in an assignment which is submitted to the school, marked by the school's tutors and returned to you with any relevant suggestions, comments, and if necessary, extra reading.


  • Describe a range of pathological problems that affect plants.
  • Describe symptoms of a range of diseases that affect plants.
  • Describe disease life cycles and explain how this knowledge can be applied in disease control
  • Explain the methods used to control diseases
  • Demonstrate a comprehensive knowledge of a particular plant pathogen.
  • Identify and describe a range of non-infectious diseases and problems that affect plants
  • Identify and describe a range of common pathogens that affect ornamental plants.
  • Identify and describe a range of common pathogens that affect crop plants

What You Will Do

  • The first part of the course develops an understanding of the different types of problems which can occur and how to identify them.
  • Terminology is covered in some depth, so as to enable the student to be able to read & understand books & articles written about plant diseases. Other major topics of study include "symptoms" (ie: Necroses, Hypoplases, Hyperplases, etc), "types of pathogens" (ie: Viruses, bacteria, fungi, Nematodes, etc), and the lifecycle of a disease.
  • The second part of the course looks at how to control pathologyproblems. The major methods of controlling pathogens (ie: Sanitation, resistant varieties, biological controls, soil drenches & chemical sprays, etc) are all studied, along with types of equipment & safety.
  • The third part of the course looks at some of the most common plant pathology problems in commercial horticulture, how to identify them and how they are controlled.
  • Some of the problems studied include cinnamon fungus, tree decay, powdery mildew, nematodes, brown rot, blights, turf fungi, damping off and non infectious problems such as temperature burns, air pollution, wind burn and excessive light.
  • The course is a highly practical one involving as much time in practical/field work as it does theory.
  • No prior formal training is required, though anyone undertaking this course is expected to have some experience in horticulture (either having worked in the industry or having studied in some related discipline.




Necroses refers to death of parts of, or whole plants. Normally protoplasts degenerate, followed by the death of cells.

  • Plesionecrotic ‑term to describe cells which are almost dead.
  • Holonecrotic ‑term used to describe cells which are completely dead.
  • Plesionecroses ‑yellowing, wilting or hydrosis (ie: very wet tissue), are common plesionecrotic conditions.

Yellowing is seen when chlorophyll breaks down. (This is different to chlorosis ‑ chlorosis is when chlorophyll does not develop in the first place). Though yellowing and chlorosis are often used as interchangeable terms, they are in fact distinctly different.

Wilting involves drooping of plant parts, caused by a loss of turgor (ie: pressure) within the cells. Wilting can be due to either:

  • Water deficiency in the soil.
  • Water uptake being stopped by some other disease problem.

Hydrosis ‑tissue becomes water soaked, cell membranes have been broken and liquid released...this often preceedes fungal rots, spots or blight.


Browning or blackening of part of a diseased plant....sections of tissue die completely....can occur in any part of a diseased plant.

There are three main types of holonecroses....

a/ Necroses of Storage Organs

  • Occurring in fruit, seed, bulbs, corms, rhizomes, tubers and roots
  • Frequently (but not always) hydrosis, followed by a blackening of tissue and eventually rot.

b/ Necroses of Green Plant Tissue

  • Typical examples include damping off, spot diseases (where spots of tissue die), streak diseases where streaks of tissue die, etc.

c/ Necrosis of Woody Parts

  • Canker where part of the bark, stem/trunk or roots die.
  • Die back and gummosis are other examples.


Failure of plant parts to develop fully (eg: Dwarfing, rosetting, etoliation, moasic, etc.).


This refers to abnormal development of plant parts, or overdevelopment of the entire plant.

Includes: Curl of leaves or shoots, club root, fasciation.

Hyperchromes....Development of abnormal colour eg: Bronzing, virescence (chlorophyll where it doesn't normally occur).

Metaplasia....Where a plant part changes to another type of plant part, which it should not be (eg: part of a flower developing a leaf like structure).

Prolepsis....Premature development of plant parts. eg: a shoot starting to grow from a bud prematurely, then dying back.


• Reputation: well-known and respected in horticulture
• Industry focus: courses designed to suit industry needs and expectations
• Different focus: develop problem solving skills that make you stand out from others
• Hands on: develop practical as well as theoretical skills
• Lots of help: dedicated and knowledgeable tutors (Faculty of internationally renowned horticulturists)
• Efficient: prompt responses to your questions
• Reliable: established in 1979, independent school with a solid history
• Up to date: courses under constant review
• Resources:  huge wealth of constantly developing intellectual property
• Value: courses compare very favourably on a cost per study hour basis
• Student amenities: online student room, bookshop, ebooks, acs garden online resources.


  Dr. Lynette Morgan

Broad expertise in horticulture and crop production. She travels widely as a partner in Suntec Horticultural Consultants, and has clients in central America, the USA, Caribbean, South East Asia, the Middle East, Australia and New Zealand.
  John Mason

Parks Manager, Nurseryman, Landscape Designer, Garden Writer and Consultant. Over 40 years experience; working in Victoria, Queensland and the UK. He is one of the most widely published garden writers in the world; author of more than 70 books and editor for 4 different gardening magazines. John has been recognised by his peers being made a fellow of the Institute of Horticulture in the UK, as well as by the Australian Institute of Horticulture.
  Rosemary Davies

Leading horticultural expert in Australia. Rosemary trained in Horticultural Applied Science at Melbourne University. Initially she worked with Agriculture Victoria as an extension officer, taught horticulture students, worked on radio with ABC radio (clocking up over 24 years as a presenter of garden talkback programs, initially the only woman presenter on gardening in Victoria) and she simultaneously developed a career as a writer. She then studied Education and Training, teaching TAFE apprentices and developing curriculum for TAFE, before taking up an offer as a full time columnist with the Herald and Weekly Times and its magazine department after a number of years as columnist with the Age. She has worked for a number of companies in writing and publications, PR community education and management and has led several tours to Europe. In 1999 Rosemary was BPW Bendigo Business Woman of the Year and is one of the founders and the Patron, of the Friends of the Bendigo Botanic gardens. She has completed her 6th book this year and is working on concepts for several others. Rosemary has a B Ed, BSc Hort, Dip Advertising & Marketing
  Simon Lennard

Simon has over 25 years experience in commercial horticulture and research. Simon has a Bachelors Degree in Horticultural Science and a Masters in Horticultural Science from Massey University New Zealand. Simon has a M.Hort.Sc.
  Organic Gardening
For decades farmers have relied upon chemicals to control pests and diseases in order to produce saleable crops. In the ornamental, vegetable and fruit gardens reliance on chemical controls has also been the mainstay for many gardeners.
  Starting a Garden or Landscape Business
Expert advice on how to get started in your own garden or landscape business! Packed with valuable business advice, horticultural and landscaping knowledge, and practical ideas - this book is a must have for garden lovers. It is great for anyone thinking about (or already involved in), a horticultural, landscaping or garden business. This updated re-print is only available as an ebook.
A good cross section of of common weeds are illustrated and reviewed. These are plants that occur in many parts of the world, and some are not always weeds.
  Plant Pests & Diseases
Are you one of those people that kill every plant you touch? Perhaps it's not you. Perhaps it's a pest or disease. A little bit of reading might just turn your garden into an oasis. Learn how to identify pests and diseases and bring the spring back into your plant...visit the bookshop to find out more...