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Common Tree Diseases in Australia: What You Need To Know

Tree disease is defined as any deviation in the normal functioning of the plant that is caused by a persistent agent. This agent may be any environmental factor, animals, insects, fungi, or basically anything that disrupts the normal functioning of the tree.

Here in Australia, trees are our greatest assets. When we talk about the beauty of nature in this country, we couldn’t miss mentioning the abundance of unique evergreen that we have. Our backyard, courtyard, and orchards have surely a tree that we’re proud of. 

Nevertheless, when disease and other forms of tree infestation arise, we got a problem at hand.

The species of trees found in Australia are known for their resilience and toughness. However, they are not invincible and are prone to acquiring different kinds of diseases over their lifetime. 

If you love your trees, you have to know how to take care of them. Here is some information about tree diseases we love to share with you.

Early Signs of Tree Diseases

It is best for you to know the early signs of tree diseases in order to promptly intervene. The earlier you can apply treatment to your tree, the better are the chances for recovery.

Here are the early signs of tree diseases you should watch for:

Reduced and Discoloured Foilage

The state of foliage and leaves are obvious indicators of the tree’s health. During the summer and spring, there should be full leaf coverage. Unusual changes in leaf appearance, decreased foliage, and discolouration is indicative of tree disease. 

Tree Bark Changes

An unhealthy tree can be diagnosed by checking its bark. If you see cracks, unusual peeling, or changes in the consistency of the bark, then there’s something wrong with the tree. The presence of fungus and destructive insects are also an indication that your tree is sick.

What Causes Stress in Trees?

Stress is something common to all living things. Trees experience stress too. Trees are maybe just too sensitive, right?

What causes stress on trees? You’d be surprised to know that the stressors affecting trees are more common than you may have thought. Aside from the visual cues, there are important things to know about when your trees are under stress.

Here are situations that can cause stress on trees:

Installation Mismatch

There are situations where you could expose your young trees to stress right at the very start of installation. Planting the tree in wrong conditions like mismatched soil, improper depth, and location can be very stressful. 

Trees that have been under stress for months or years will show several tell-tale signs such as stunted growth, discolouration of bark and leaves, and even sudden death. 

Improper Pruning and Mulching

Regular tree maintenance activities like pruning and mulching can cause stress to your plants if done incorrectly. Improper techniques can lead to problems you’ll later see. 

Pruning during the wrong season could be dangerous as you’ll be exposing the tree to insects and diseases. There are also rules to follow in terms of the type of tree and the size to be pruned.

Too much or too little mulch can also be harmful. Too much mulch can lead to rotting of the roots due to excessive moisture. Too little mulch, of course, would have little to no effect. Make sure you understand the principles of mulching before doing it yourself. 

Poor Maintenance of Trees

Most trees can grow and live without needing any assistance. However, there may be some species that require attention and maintenance. 

Top 10 Common Tree Diseases in Australia

The most common cause of tree diseases in Australia are fungi and insect infections. They are continuous threats that we need to understand and learn how to identify. 

Here is the list of the most common tree diseases in Australia:

  1. Cypress Canker

This tree disease is a water-borne infection. This has plagued a lot of Cypress trees in Australia over the years. Cankers are caused by fungi and appear as deep red colour on branches causing them to die very quickly. Some reports say branches die within 24 hours.

Following the death of branches, spores are released by the fungi to affect other healthy branches. The cycle repeats until the whole tree dies and other nearby trees are affected as well. The good news is this disease is easily managed. Cutting the affected branch will prevent the spread to other parts of the tree.

  1. Myrtle Rust

First detected in 2010, this fungal infection causes bright yellow powdery spots on the leaves of the tree. The leaves will turn brown or grey before eventually dying. The spores are easily transmittable through the air and would require rigid fungicide treatment and quick isolation measures.

  1. Pink Disease

This tree disease affects a wide variety of trees in Australia. The fungal pathogen grows within the bark and makes it swell, split and kills the tree in a short time. This disease has caused a lot of headaches to farmers of citrus trees in NSW, Queensland and the Northern Territory.

When removing branches afflicted with Pink disease, it is best to burn them immediately to prevent the spreading of the spores to other plants.

  1. Citrus Gall Wasp

This bark infection is caused by the Gall Wasp. The insect lay its eggs in the branches of the tree then the infection starts. The presence of these eggs will cause the branches of the tree to bulge and swell. You have to act quickly by cutting the affected branches to prevent the cycle of infection from repeating and spreading across the whole tree.

  1. Root Rot

Root rot is the rapid decaying of a plant’s root system while it’s still alive. Signs of root rot include the appearance of small, discoloured, wilted leaves. The branches also show signs of decay. Root rot is difficult to diagnose and you may need the help of an arborist to help you in managing this tree disease.

You can avoid root rot by keeping the soil well-cultivated and ensuring there’s efficient drainage around the tree.

  1. Oak Wil

Oak wilt is caused by a soil-borne fungus that is spread by beetles. Signs of Oak Wilt include the appearance of wilted, rust coloured leaves that are present even if it is in season. This is a very fast-acting infection that can kill a tree within a single season. 

However, managing this type of tree disease is fairly easy. You have to build a trench around the roots of the affected tree. Cut the roots to keep the infection from spreading to nearby trees. You should act fast though as infection of this type spread very fast.

  1. Peacock Spot

Commonly seen among olive trees across the world, this tree disease is caused by fungi leading to stunted growth, blemishes, and delayed fruit ripening. Sooty blotches appear on the leaves of the plant which then develop into black circular spots with a yellow halo.

Treatment of this tree disease involves spraying the foliage with copper compound. 

  1. Tree Leaf Diseases (Teratospaeria)

This type of disease is common among gum trees but affects eucalyptus trees as well. A group of fungi infect the trees affecting the leaves. The infected leaves’ appearance depends on the type of fungus that caused the disease. You need to watch out for spots that are of a different colour (purple, red, brown, yellow) with black spores alongside them.

  1. Anthracnose

This fungal infection affects the growing leaves of trees. The pathogen eats through the leaves leading to holes and extreme defoliation. Damp and wet environments are factors that may lead to overgrowth and proliferation of the fungi.

Management and treatment of Anthracnose infection involve cutting the affected part and burning it to prevent the spread of infection. 

  1. Emerald Ash Borers

These little beetles can cause severe destruction to your tree if left unattended. The bark of your trees is the primary target of these pests. They bore holes and create tunnels inside the tree.

If you notice discolouration in the leaves and dying branches of Ash trees during the spring, these creatures are surely present. Insecticides can be helpful to some extent but it is not totally reliable. Trees infected with Emerald Ash Borers should be removed.

Final Thoughts

The care of our beloved trees lies in our hands. We have to remember that we have an obligation to keep the trees in our properties healthy. Proper tree maintenance can be easy but you need adequate knowledge and skills to do that.

If you are unsure if your trees are healthy, under stress, or afflicted with disease, it is best to call on professional arborists to help you in assessing the condition of your plants. They can properly diagnose and recommend specific treatments for your sick trees.

Trees Down Under