Understanding Plant Health Problems

There are a wide range of things that can harm your plants.

The confined nature of small gardens may serve as an advantage or disadvantage.
Walls or fences can be a barrier to pests, diseases, and even undesirable weather.
These same walls and diseases can however, in other instances encourage problems.
They may restrict predators from moving into the area and attacking pests.
Diseases can be incubated and encouraged by poor ventilation, higher humidity and warmer temperatures that often characterize enclosed spaces.
If a plant is not healthy, and you want to determine what is wrong, you need to be systematic in your approach.
There are really only four broad possibilities. Plant problems can be grouped broadly into the following:



Animals of various sizes and forms (from microscopic worms to dogs, birds, grazing animals, even humans). Insects are just one of many groups of animals which can cause damage to plants, although they are perhaps the most significant group of plant pests. Most pests cause damage above the ground, and either the pest, or the damage is usually obvious. Look for signs of insects or other animals. Bite marks, scratches, breakages, trails (eg. slime marks of snails) or droppinds (tine faeces from grasshoppers) will all indicate a pest.


These are problems caused by living organisms other than animals. Fungi, bacteria and virus are the most common. Diseases frequently cause damaged patches of tissue, rotting, discolouration or abnormal growths. When a disease is serious, the growing tips of a plant are not lush and healthy.

Environmental Disorders

Troubles caused by soils, nutritional problems, bad weather conditions such as frost, wind, cold, heat, or poor drainage. If the condition of a plant changes very suddenly, you should first consider what sudden environmental have occurred recently. If the weather went cold or hot; or you had abnormal rain or drought; you can probably assume that this was the problem. When a plant deteriorates more gradually, you need to consider things that could have changed gradually (eg. The soil gradually ran out of nutrients, or gradually became more compacted).


Weeds are plants growing where you don't want them. It is the location of a plant which makes it a weed, NOT the species of the plant. A weed will compete with your desired plants for nutrients, water, space which can be harmful to your desired plants. If weeds are your problem, their presence will be obvious.




The most obvious way to control pests or diseases is to use a chemical spray; but this is often not necessary. A reasonably healthy plant will usually overcome a mild infection without any treatment. If the diseased part is isolated, it can be simply pruned off and burnt. Feeding and watering the plant can also be helpful; increasing the plants ability to withstand the problem

If the problem is more serious, you can treat it with a spray. The first option should always be a milder chemical, which is less likely to damage beneficial animals such as earthworms and birds. Pyrethrum is a good relatively safe insecticide that you can try for most insects. Bordeaux, or another copper spray, is a relatively safe fungicide that will help control most fungal diseases.

Any qualified nurserymen can provide more advice if you need it.

Whatever you decide to do though; always remember to read and follow instructions on the label.




Chemicals, both natural and unnatural are used by gardeners to kill pests and disease, eradicate weeds, improve soils or feed plants. They can be applied any of the following ways:


The chemical is mixed into a solution and sprayed onto the plant. This is relatively easy to do with the right equipment, and spreads the chemical evenly (which is important if it is to do the job), but can have a few problems:

On a wet day, the rain dilutes the chemical and that may affect the result (So don't spray on wet days!)

On a hot day, moisture can evaporate quickly making the spray more concentrated, and that can affect the job; maybe even burning the plant (so don't spray on a hot day!)

On a windy day spray mist can drift. It can blow on you or other people causing poisoning. It can blow into neighbouring properties affecting plants, animals or even insects which you don't want to affect.

In a liquid form, chemicals are more readily absorbed into your skin, particularly if you are sweating. (Be careful!)


This involves blowing or shaking a fine powder over plants. The major problem is in windy weather where more of the chemical can end up off the plants than on them.

By Hand

These are chemicals which are sprinkled on the soil and gradually break down with rain or watering to move into the plant's roots. Only certain types of chemicals work this way. Examples:

Solid fertilisers

Granular insecticides and fungicides which are absorbed into the roots of a plant and moved through the plant's sap system (eg. Disyston).

Granular chemicals which kill disease spores, insects or weed seeds which are in the soil, and may at a later stage affect the plant.

With Irrigation (Through A Sprinkler System)

Some chemicals can be added to the irrigation system and sprayed onto plants through sprinklers or dripped onto the roots through drippers. Only certain types of chemicals are suited to this method of application. Such chemicals need to act quickly, because the irrigation which applies them will also wash them away from the plant.


This involves directly pouring or injecting a chemical into the sap system of a plant. It is by far the safest method of applying chemical because it cannot drift or spread to places away from the plant. Unfortunately, this method only works with chemicals which have the ability to move through the sap system of the plant. It's main use is for treating large trees.



ONLY use chemicals when actually needed!

Use the correct chemical for the job at hand, if unsure; seek advice.

Always read the label, and the product information sheets (if available)

Use protective clothing at ALL times.

Use the correct pesticide application equipment.

Don't spray on windy or very hot days!!!!

Warn other people in the area that you are going to spray (and have sprayed)

Wash out all spray equipment thoroughly when finished.

Do not eat or smoke while spraying.

Wash all protective clothing thoroughly after spraying.

Wash yourself thoroughly after spraying -especially the hands.

Wash and Store spray equipment and chemicals in a safe, locked place.

Dispose of empty pesticide containers according to the label instructions.

Record all details of your spraying.



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