Common Tree Diseases in Sydney: Identification & Treatment Guide

Recognising Tree Disease: Warning Signs

Trees can suffer from numerous diseases, and early detection is crucial for successful treatment. Here's what to watch for in your Sydney garden:

• Unusual leaf discolouration: Yellowing, browning, or spotting outside normal seasonal change
• Premature leaf drop: Losing leaves significantly earlier than normal
• Wilting: Drooping leaves or branches despite adequate water
• Abnormal growths: Cankers, galls, or unusual bumps on bark
• Fungal fruiting bodies: Mushrooms or conks on trunk or at base
• Dieback: Progressive death of branches from the tips inward
• Oozing or bleeding: Sap or unusual liquids leaking from bark

Common Tree Diseases in Sydney

Myrtle Rust (Austropuccinia psidii)

One of the most significant tree diseases affecting Sydney, Myrtle Rust attacks plants in the Myrtaceae family—a group that includes many Australian natives.

Affected Trees

• Lilly Pilly (Syzygium species)
• Bottlebrush (Callistemon)
• Tea Tree (Melaleuca, Leptospermum)
• Eucalyptus (some species)
• Rose Apple, Guava

Symptoms

• Bright yellow-orange pustules on new growth
• Distorted, curled, or puckered leaves
• Brown, dying shoot tips
• Progressive dieback in severe cases

Management

• Prune out and dispose of infected material carefully (don't compost)
• Apply copper-based fungicides as a preventive
• Consider resistant varieties for new plantings
• Severe cases may require tree removal

Phytophthora Root Rot

A devastating water mould that attacks root systems, particularly in poorly drained soils or after wet periods.

Affected Trees

• Oaks
• Avocados
• Some eucalypts
• Many natives in waterlogged conditions

Symptoms

• Yellowing leaves that don't respond to fertiliser
• Crown dieback progressing through the tree
• Dark, water-soaked appearance at trunk base
• Roots that are brown/black instead of white
• Sudden collapse in advanced cases

Management

• Improve drainage around affected trees
• Avoid overwatering and soil compaction
• Phosphonate injections may help in early stages
• Severely affected trees may need removal to prevent spread

Armillaria Root Rot (Honey Fungus)

A serious fungal disease that spreads through the soil, attacking stressed trees and spreading to healthy ones via root contact.

Symptoms

• Honey-coloured mushrooms at trunk base (autumn)
• White fungal sheets under bark near soil level
• Dark, bootlace-like rhizomorphs in soil
• Progressive dieback and decline
• Resin bleeding from lower trunk

Management

• No chemical cure available
• Remove infected trees including stumps and major roots
• Avoid replanting susceptible species in same location
• Improve tree health to increase resistance

Cypress Canker

Common on cypress, juniper, and related species throughout Sydney suburbs.

Symptoms

• Patches of yellow then brown foliage
• Sunken, cracked cankers on branches and trunk
• Resin oozing from affected areas
• Progressive branch death

Management

• Prune out affected branches well below visible infection
• Sterilise pruning tools between cuts
• Improve tree vigour through appropriate watering and fertilising
• Severely affected trees may require removal

Sooty Mould

A black, soot-like coating on leaves caused by fungus growing on honeydew excreted by sap-sucking insects.

Symptoms

• Black coating on leaf surfaces
• Reduced vigour due to blocked photosynthesis
• Sticky honeydew residue
• Presence of aphids, scale, or other sap-sucking insects

Management

• Treat the underlying insect problem first
• Mould will wash away naturally once insects are controlled
• Horticultural oil sprays help control insects and clean leaves
• Pruning can improve air circulation

When Fungi Indicate Serious Problems

Seeing mushrooms or bracket fungi on your tree? This often indicates internal decay:

Bracket Fungi (Shelf Fungi)

• Hard, shelf-like growths on trunk indicate advanced internal decay
• The tree may appear healthy but be structurally compromised
• Professional assessment is essential for safety evaluation

Mushrooms at Base

• Often indicate root decay or Armillaria infection
• Tree stability may be compromised
• An arborist assessment is recommended

Pest-Related Diseases

Insects often introduce or spread disease while creating wounds for infection:

Longicorn Borers

Beetles that bore into stressed trees, introducing fungi and bacteria:

• Small entry holes in bark (2-5mm)
• Sawdust accumulation at hole sites
• Branch or tree dieback
• Often targets stressed or declining trees

Psyllids

Sap-sucking insects that can cause significant damage and disease spread:

• Lilly Pilly Psyllid causes bumpy, distorted leaves
• Creates stress that makes trees susceptible to other diseases
• Regular pruning and healthy growing conditions help control

When to Call an Arborist

Contact a professional arborist if you notice:

• Fungal growths on the trunk or at the base
• Significant dieback (more than 10-15% of canopy)
• Large cankers or wounds on the trunk
• Sudden or severe decline in tree health
• Oozing or bleeding that doesn't stop
• Disease spreading to multiple trees

Professional assessment can determine whether treatment, targeted pruning, or removal is the best option.

Preventing Tree Disease

• Avoid wounding: Protect bark from mower and whipper snipper damage
• Prune correctly: Use proper techniques to minimise wound size and promote healing
• Improve drainage: Many diseases thrive in waterlogged soils
• Maintain vigour: Healthy trees resist disease better
• Clean tools: Sterilise pruning equipment between trees
• Mulch properly: Keep mulch away from trunk to prevent collar rot
• Regular inspection: Catch problems early when treatment is most effective

Frequently Asked Questions

Can a sick tree infect other trees?

Yes, many tree diseases spread through soil, root contact, air-borne spores, or insect vectors. Early removal of severely infected trees can protect nearby healthy trees.

Should I fertilise a sick tree?

Not necessarily. Fertilising a tree with root disease can worsen the problem. Get a professional diagnosis before treating symptoms.

How much does tree disease treatment cost?

Treatment costs vary widely—from $50 for basic fungicide application to $500+ for phosphonate injections or extensive pruning. An arborist can assess and quote appropriate treatments.

Can diseased trees be saved?

Many can, especially with early intervention. However, some diseases (like advanced Armillaria) have no cure, and removal becomes necessary to protect other trees and property.