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Plant Pathology

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

Become Skilled at Diagnosing and Understanding Plant Diseases

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 & 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.

This course is a must for horticulturalists who want to boost their plant health knowledge and prevent damage by pests and diseases in different settings (gardens, nurseries, parks, public landscapes, farms, market gardens).

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


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 pathological problems. 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.


Nematodes are tiny, often microscopic worms. They can cause plant diseases. Also called eelworms,they result in plant infections worldwide.  There may be as many as half a million different kinds, yet only about four dozen genera are important plant parasites.
Nematodes are worm shaped, most kinds ranging in length from 0.5mm to 2.0mm.  The majority are only 0.15mm to 0.2mm in diameter.
Many nematodes are not parasitic or pathogenic on plants. Some are parasitic on animals, including man.  Others are not parasitic at all, living in the sea, sand or soil.  Their feeding habits and habitats vary, as does their physiology.  It is thought that almost any organism may serve as a source of food for one kind of nematode or another.
All nematodes have sensory organs and nervous systems.  All live in water, or in a thin film of water around soil particles, moving about by contracting and relaxing their muscles.  Some can withstand dessication. Many are capable of assuming a low state of metabolism or quiescence under stress conditions. Nematodes respond to temperature, light, soil type, pH, gravity, moisture and chemicals liberated from the microenvironments of living roots.
Nematodes which are harmful to plants can be characterised by their feeding habits.  Most of these attach to roots or below ground plant parts but a few migrate to leaves and stems.  Those which feed on the root surfaces without complete entry are termed ectoparasites.  Those entering roots completely are called endoparasites.  Both groups, at some point, can be migratory (moving about, feeding without becoming attached) or sedentary (becoming attached, and not moving about).
All plant parasitic nematodes possess a hollow, protrusible spear or stylet which is used to puncture plant cells.  A median bulb acts as a pump to inject saliva or withdraw cell contents during feeding.
The type and extent of root damage depends on the species of nematode, the plant, and the nematode population. Generally, roots have abnormal growth (stunted or enlarged) as the result of nematode attack.  Root knots or galls are enlargements caused by the feeding of root knot nematodes, perhaps the most common nematode recognised in home gardens.  
Lesions appear as areas of darkened tissue after nematodes have been feeding.  Sometimes, the lesions encircle the root impairing its function.  Another root symptom is excessive branching in the area of nematode activity.
Nematodes often feed just behind the growing root tip which results in shortened, stubby roots.  Some nematodes can migrate to above ground plant parts where they cause dead areas on leaves and distortion of stems.
Although the feeding activities of these transparent worms inflict mechanical damage to plants, the greatest effects are those caused by the chemicals that are injected into the plant by the nematodes which result in changes to the plant's metabolism.  Nematodes are also carriers of certain plant viruses, and they can be the means by which other disease organisms gain entrance to the plant.  For instance, one of the common wilt diseases of tomato is caused by the fungus called Fusarium oxysporum.  When the root knot nematode is present along with the fungus in the same soil, the disease is accentuated.  It is thought to be more than a mere wounding effect by nematodes, although, in themselves, they can be very effective in reducing water and nutrient uptake by damaging the roots.



Meet some of our academics

Rosemary Davies Journalist, Editor, Broadcaster, Teacher and Consultant for over 30 years. Rosemary is former gardening editor for the Weekly Times (a Weekly Farming Newspaper in Australia); and author of six books in her own right. She has written articles for many magazines across Australia, and has since 2008 worked as a tutor and freelance writer with ACS; contributing to books a range of genres.
Dr. Lynette MorganBroad 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.
Diana Cole B.A. (Hons), Dip. Horticulture, BTEC Dip. Garden Design, Diploma Chartered Institute of Personnel & Development, PTLLS (Preparing to Teach in the Life Long Learning Sector), P.D.C. In addition to the qualifications listed above, Diana holds City & Guild construction qualifications and an NPTC pesticide spraying licence (PA1/PA6). Diana runs her own landscape gardening business (Arbella Gardens). Active in many organisations including the British Trust for Conservation Volunteers.

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