An in depth plant health course. Study plant pests, diseases, environmental damage; causes, diagnosis and treatments. Work in horticulture caring for plants.

Course Code: BHT116
Fee Code: S2
Duration (approx) Duration (approx) 100 hours
Qualification Statement of Attainment
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Learn about plant health, to systematically identify health problems in plants, and control those problems

  • Professional development for gardeners, pest control operators, nurserymen, anyone who works with plants
  • Extend and deepen your skills -advance your career or business
  • Study at your own pace; from anywhere, anytime.
A sick plant may have one, or several causes; all at the same time.

There are thousands of possible causes which can contribute to a plant's problems. More often than not, there are several factors involved. Minor diseases or environmental problems may weaken the plant, making it susceptible to some more major (obvious) disorder. When you inspect a plant for problems, you should systematically consider all of the things which might possibly be going wrong. This course provides the foundation for inspecting diagnosing and treating all types of problems.


Lesson Structure

There are 10 lessons in this course:

  1. Introduction
    • Pests
    • Diseases
    • Common terminology
    • Diagnosing problems systematically
    • Tell tale symptoms
    • Conducting an inspection: four steps
    • Pest or disease reviews
  2. Overview of Preventative Controls
    • Introduction
    • Methods of pest management
    • Integrated pest management
    • Cultural control
    • Using disease resistant varieties
    • Crop rotation
    • Timed planting
    • Mulching
    • Cleanliness
    • Biological control
    • Types of biological controls
    • Beneficial plants
    • Trap or decoy plants
    • Pheromone traps
    • Physical controls
    • Traps
    • REpellants
    • Mulching
    • Pruning
    • Wounds
    • Chemical controls
    • Understanding pesticides
    • Safely storing chemicals
    • Safely mixing chemicals
    • Legalities
    • Plant breeding for resistance
    • Sources and causes of resistance
    • Adaptability, resistance and pest variability
  3. Insecticides
    • Types of insecticides: systemich, stomach poisons, contact poisons, etc
    • Inorganics, botanicals, organophosphates, carbamates, synthetic pyrethroids
    • Characteristics of insecticides: toxicity, spectrum, LD50, persistence, volatility, etc.
    • Golden rules for handling pesticides
    • Terminology
  4. Other Pesticides
    • Chemical Pesticides: introduction
    • Review of common pesticides
    • Soil treatment for control of diseases
    • Soil pests
    • Types of fumigtants
    • Systemic fungicides
    • Comparative toxicities
  5. Spray Equipment
    • Types of sprayers
    • Uses of sprayers
    • Spray terminology
    • Sprayer maintenance and cleaning
    • Selecting a sprayer
    • Calibration
    • Using chemicals: agitation, clean up and disposal
    • Basic first aid with chemical pesticides
    • Response to liquid or powder spills
    • Keeping records
    • Misters, Dusters, Blowers
    • Pesticides and the environment
  6. Insect Biology
    • Insect classification: orders, sub classes
    • Insect anatomy: mouthparts, legs, etc
    • Lifecycle
    • Feeding habits
    • Practical project: Insect collecting, preserving, identifying, for an insect collection
    • Common insects that a gardener encounters
    • Ants
    • Aphis
    • Beetles
    • Borers
    • Bugs
    • Caterpillars
    • Cockroaches
    • Crickets
    • Earwigs
    • Fleas
    • Flies
    • Galls (caused by insects)
    • Grasshoppers
    • Ladybirds (good and bad)
    • Leaf hoppers
    • Leaf miners
    • Lerps
    • Mealy bug
    • Mosquitos
    • Scale insects
    • Termites
    • Thrips
    • Wasps
    • Whitefly
  7. Fungal Biology
    • What causes disease
    • Symptoms of disease
    • Lifecycle of a disease: inoculation, penetration, infection, growth and reproduction, dissemination
    • Fungi groups: obligate saprophytes, obligate parasites, facultative saprophytes, facultative parasites
    • Expanded concept of tree decay
    • Chemical pesticides in the UK and Europe
    • Common diseases
    • Anthracnose
    • Bitter pit
    • Blights
    • Botrytis
    • Canker
    • Cinnamon fungus
    • Club root
    • Damping off
    • Galls
    • Gummosis
    • Leaf curl
    • Leaf spot
    • Melanose
    • Mildews
    • Rots
    • Rust
    • Scab
    • Silver leaf
    • Spot
    • Smut
    • Sooty mould
    • Wilts
  8. Environmental Problems
    • Common environmental problems
    • Foliage burns
    • Pollution
    • Lack of water
    • Drainage problems
    • Frost
    • Hail
    • Shade
    • Temperature
    • Wind
    • Symptoms of nutritional deficiencies
    • Air pollution
    • The plant and water
    • Non parasitic problems in turf (lawns)
    • Ways to provide environmental protection to plants
  9. Viruses
    • Overview
    • Symptoms
    • Detection and diagnosis of viruses
    • Control
    • Examples of virus diseases
  10. Nematodes, Molluscs and Crustaceans
    • Overview
    • Millipedes
    • Plant nematodes
    • Nematodes in citrus
    • Red spider mites
    • Spiders
    • Slaters or wood lice
    • Snails and slugs


  • Identify the characteristics of pests and diseases of plants.
  • Explain methods for the control of pests and diseases.
  • Describe the characteristics of a range of different pesticides, including:
    • insecticides
    • and fungicides.
  • Explain the selection and use of spray equipment appropriate for different specified tasks.
  • Describe aspects of the biology of an insect which are relevant to pest control.
  • Describe aspects of the biology of an fungus which are relevant to disease control.
  • Explain how inappropriate environmental conditions can affect plant health.
  • Identify the characteristic signs of a range of non-insect pests, and select appropriate control methods.

Here are just some of the things you will be doing:
Develop a checklist for determining the significance of pests and diseases, which addresses different criteria including:
  • short term impact
  • long term impact
  • economic impact
  • aesthetic impact.
Distinguish between the main types of plant diseases, including:
  • fungal
  • viral
  • bacterial.
Create a standard worksheet for reviewing pest and disease problems of plants.
Diagnose twenty different problems (ie. pests or diseases), documenting the problem on a standard pest/disease review worksheet.

Describe different ways to control pests and diseases, including:

Application of chemicals
  • Plant selection
  • Companion planting
  • Cultural techniques (i.e. improving ventilation, improving drainage)
  • Physical control (i.e. pruning, hand removal, trapping, hosing off).

Explain how plant breeding has been used to improve pest/disease resistance in two different plant species.

Explain three biological control methods for dealing with specific problems.

Develop an IPM strategy for a specific situation such as a crop or garden, considering: application procedures, remedial action and monitoring.

Describe plant hygiene practices for a specific situation such as a crop, nursery or garden, in line with industry practice, enterprise guidelines and sound management practice.

Recommend control methods for five different pest and/or disease problems which you diagnose.

List safety procedures to follow when handling pesticides.

Distinguish between the main groups of pesticides, including:

  • organo-phosphates
  • synthetic pyrethroids
  • carbamates
  • chlorinated hydrocarbons.
Explain the difference between the action of systemic and non-systemic pesticides.

Explain maintenance practices, including cleaning, for a specified sprayer.

List three different uses for each of three types of sprayers, including a motorised pump sprayer, a knapsack and a PTO driven tractor mounted sprayer.

Compare six different sprayers, in terms of:

  • cost
  • applications
  • maintenance
  • spare parts
  • ease of use
  • safety.

Explain the application of chemicals in a given situation, including:

  • Calibration
  • Mixing chemicals
  • Equipment operation
  • Safety measures
  • Post spray procedures such as cleaning, and storage of chemicals).

Describe the minimum records which should be kept when spraying pesticides.

Prepare a labelled diagram showing the structural parts of an insect.

Prepare an insect collection of at least fifteen insects of significance to agriculture or horticulture.

Identify to genus level, the insects collected.

Compare the structural differences between three different types of insects.

Describe the lifecycle of an insect species.

Explain how an understanding of insect lifecycle can be applied to pest control.

Describe the lifecycle of one fungal disease species.

Explain the physiology of tree decay processes, including compartmentalisation.

Explain aspects of fungal biology, for different types of fungi, which are of horticultural significance,  including:

  • Phytophthora
  • Sclerotinia rot
  • Peach leaf curl (Taphrina deformens)
  • Powdery Mildew
  • Pythium.

List environmental problems which affect plant health and their symptoms.

Describe the affect of air pollution on two different plants.

Identify nutritional deficiency symptoms in three specified situations.

Develop a fertiliser program in response to a specified nutritional problem.

Distinguish between the affects of water deficiency and water excess on plant health.

Explain how to diagnose damage by various non-insect pest problems, including:

  • Nematodes
  • Slugs and snails
  • Mites
  • Millipedes
  • Larger animals such as rabbits, rodents or birds.
Explain how to control different non-insect pests with both chemical and non-chemical methods. 

Understanding Disease in Plants

Diseases can strike even the most well cared-for garden and knowledge of plant pathology is vital to help identify diseases of your plants. Plant pathology is the section of botanical science which deals with diseases and troubles in plants.

Plant pathology is generally distinguished from insect and other pest problems. Plant pests actually eat the plant, or break the plant by standing on it. Plant diseases are different.

Plant diseases are far more subtle, disturbing the microscopic physiological processes which go on within the plant. It can be caused by environmental factors, or through viruses, bacteria, fungi and other organisms.


When looking at any disease, the following things need to be considered:

1) The name of the disease.

2) The species of plants which are susceptible to that disease.

3) The importance of the disease.

  • What parts of the plant are affected and the way they are affected.
  • The extent of damage to the plants affected.

4) Symptoms   what they are and how to identify them.

5) What the disease organism does to the plant and how it does it.

6) How the disease spreads.

7) Control - how the disease can be controlled in infected plants, and how it might be prevented from spreading further.


The following types of organisms are the major causes of pathological problems in plants:

These are very small (microscopic) particles composed of nucleic acid and protein. They exhibit many, but not all, characteristics of living organisms and, as such, are sometimes called a life form. At other times, they are not considered to be a life form.

Viruses can mutate. They cause many serious diseases, frequently causing symptoms such as variegation, or mottling of leaf colour. Some viruses are considered beneficial because of the variations they provide in leaf colour. Whether considered beneficial or not, viruses cause a general weakening of plants they infect, making the plant more susceptible to other problems, and frequently stunting growth to some degree.

Bacteria are one of the smallest living things, being just single-celled organisms. They enter plants through stomata (leaf pores), wounds or water pores (they cannot break directly through the cell walls of the "surface" of a plant. Bacteria can cause rots, blights, spots, galls, scabs and other symptoms (Note: Fungi can also cause many of these).

Fungi are chlorophyll-less plants. They are either parasites (living on live tissue), or saprophytes (living on dead tissue). There are over 15,000 species known, and many are responsible for major plant diseases. They are thread-like organisms which grow amongst the tissue they derive their nutrition from. The individual threads are known as mycelium. To reproduce, they grow fruiting bodies from a mass of mycelium, and spores are produced in these fruiting bodies.


The most easily identified symptoms are those which cause physical change to the plant. They are helpful in identifying which disease or group of diseases is attacking a plant. Physical symptoms can be separated into two main categories:

  1. Death or near death of part or all of a plant.
  2. Improper development of plant growth.

Disease can cause the death of a plant, or of parts of a plant. This is usually visible as brown dead plant matter.

Sometimes a dying plant will struggle on, barely alive, for a long period of time. Yellowing, wilting or very wet tissue are usually symptoms of this.
Yellowing is seen when chlorophyll breaks down.
A wilting plant will have drooping plant parts caused by a lack of pressure within the plant's cells. Wilting can be due to a water deficiency in the soil, or by disease preventing water from being taken up into the plant.
Wet or water-logged tissue happens when cell membranes break and the liquid inside is released. This often precedes fungal rots, spots or blights.

Disease can also cause plants to grow abnormally. A plant may develop curl of leaves or shoots, clubbed roots, or other weird shaped growths. Plant colour can be affected, with strange variations appearing e.g. bronzing. Plant parts may develop into other types of parts e.g. part of a flower may develop a leaf-like structure, or leaves may develop woody stems on their ends. Premature development can result in shoots growing from buds too early, then dying back.



  • Professional development for gardeners, pest control operators, nurserymen, anyone who works with plants
  • Extend and deepen your skills - advance your career or business
  • Extend your knowledge as a gardening enthusiast


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UK Register of Learning Providers, UK PRN10000112

Accredited ACS Global Partner

Member of Study Gold Coast

Course Contributors

The following academics were involved in the development and/or updating of this course.

John Mason (Horticulturist)

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 edito

Rosemary Davies (Horticulturist)

Rosemary trained in Horticulture at Melbourne Universities Burnley campus; studying all aspects of horticulture -vegetable and fruit production, landscaping, amenity, turf, aboriculture and the horticultural sciences.
Initially she worked with the Depart

Maggi Brown

Maggi is the classic UK "plantswoman". She can identify thousands of plants, and maintains her own homes and gardens in the Cotswolds (England), and near Beziers (in Southern France). Maggi is regarded as a leading organics expert across the UK, having w

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