Trees are a vital part of any Australian landscape, providing shade, beauty, and environmental benefits. However, they’re also a natural target for a wide range of pests. From tiny sap-sucking insects to destructive wood-boring larvae, tree pests can weaken, damage, and even kill otherwise healthy trees if left untreated.
The good news? With the right knowledge, you can identify early warning signs and take action before serious damage occurs.
In this guide, we’ll walk you through how to identify and deal with common tree pests—especially borers, aphids, caterpillars, and other common invaders—so you can keep your trees healthy and thriving.
Why Tree Pest Control Matters
Tree pests don’t just affect appearance—they can compromise the structural integrity and long-term health of your trees.
Unchecked infestations can lead to:
- Leaf loss and reduced photosynthesis
- Stunted growth
- Branch dieback
- Increased susceptibility to disease
- Tree death in severe cases
Pests often target stressed or weakened trees, which makes early detection and proactive care essential.
Common Signs of Tree Pest Infestation
Before diving into specific pests, it’s important to recognise the general warning signs.
Look out for:
- Holes or chewed leaves
- Sticky residue (honeydew) on leaves or surfaces below
- Sawdust-like material (frass) around the base or trunk
- Discoloured or curling leaves
- Visible insects or larvae
- Wilting or branch dieback
Spotting these early can make a huge difference in how easily the problem can be controlled.
1. Borers (The Silent Killers)
What Are Borers?
Borers are among the most destructive tree pests. They are the larvae of beetles or moths that tunnel into the trunk, branches, or roots of trees.
Once inside, they feed on the tree’s internal tissues, disrupting the flow of water and nutrients.
Signs of Borer Infestation
Common indicators include:
- Small holes in the bark
- Sawdust-like frass near entry points or at the base
- Oozing sap or resin
- Dead or dying branches (often starting at the top)
- Progressive canopy thinning
Borers are particularly dangerous because damage often goes unnoticed until it’s advanced.
How to Deal with Borers
1. Improve Tree Health
Borers typically attack stressed trees. Proper watering, mulching, and soil care can make trees less vulnerable.
2. Remove Infested Wood
Prune and dispose of affected branches to stop larvae from spreading.
3. Apply Targeted Treatments
Professional arborists may use systemic insecticides or trunk injections for severe infestations.
4. Preventive Maintenance
Regular inspections are key—especially for older or drought-stressed trees.
2. Aphids (Small but Problematic)
What Are Aphids?
Aphids are tiny, soft-bodied insects that feed on sap by piercing leaves and stems. While small, they often appear in large numbers and can quickly overwhelm a tree.
Signs of Aphid Infestation
Watch for:
- Clusters of tiny insects on leaves or stems
- Sticky residue (honeydew) on leaves, cars, or ground below
- Sooty mould (black fungus growing on honeydew)
- Curling or distorted leaves
- Increased ant activity (ants feed on honeydew)
How to Deal with Aphids
1. Natural Predators
Encourage beneficial insects like ladybirds and lacewings, which naturally control aphids.
2. Hose Them Off
A strong spray of water can remove aphids from leaves.
3. Use Insecticidal Soap or Oils
Eco-friendly treatments can effectively reduce populations.
4. Control Ants
Since ants protect aphids, managing ant populations can help reduce infestations.
3. Caterpillars (Leaf Destroyers)
What Are Caterpillars?
Caterpillars are the larval stage of moths and butterflies. While some are harmless, others can defoliate trees quickly.
Signs of Caterpillar Damage
Look for:
- Chewed or skeletonised leaves
- Large sections of missing foliage
- Webbing or nests in branches
- Visible caterpillars on leaves or trunks
Heavy infestations can strip a tree of leaves in a short time.
How to Deal with Caterpillars
1. Manual Removal
For small infestations, physically removing caterpillars can be effective.
2. Biological Control
Use products containing Bacillus thuringiensis (Bt)—a natural bacteria that targets caterpillars.
3. Prune Affected Areas
Remove heavily infested branches.
4. Monitor Regularly
Caterpillar outbreaks can happen quickly, especially in warmer months.
4. Scale Insects
What Are Scale Insects?
Scale insects are small, immobile pests that attach themselves to branches and leaves, feeding on sap.
Signs of Scale Infestation
Symptoms include:
- Small bumps on bark or leaves
- Yellowing foliage
- Sticky honeydew
- Sooty mould growth
Treatment Options
- Apply horticultural oil to suffocate insects
- Prune heavily infested branches
- Introduce natural predators
5. Psyllids and Leaf Miners
What Are They?
- Psyllids cause leaf distortion and pimple-like growths
- Leaf miners tunnel inside leaves, creating visible trails
Signs to Watch For
- Squiggly lines or trails inside leaves
- Bumpy or distorted growth
- Reduced leaf health
How to Manage Them
- Remove affected leaves
- Encourage beneficial insects
- Apply targeted treatments if needed
Preventing Tree Pest Problems
Prevention is always easier (and cheaper) than treatment.
Here are key strategies:
1. Keep Trees Healthy
Healthy trees are far more resistant to pests. Ensure proper watering, fertilisation, and soil care.
2. Regular Inspections
Check your trees regularly—especially during spring and summer when pests are most active.
3. Prune Properly
Remove dead or overcrowded branches to improve airflow and reduce hiding spots.
4. Clean Up Debris
Fallen leaves and branches can harbour pests and larvae.
5. Avoid Overwatering
Excess moisture can attract pests and weaken trees.
When to Call a Professional Arborist
While minor infestations can often be managed at home, some situations require expert help.
You should contact a professional if:
- The infestation is widespread or recurring
- The tree shows structural weakness
- Borers or internal pests are suspected
- You’re unsure how to treat the issue safely
Professional arborists have the tools, knowledge, and treatments to manage pests effectively without causing further harm to your tree or surrounding environment.
Final Thoughts
Tree pests like borers, aphids, caterpillars, and scale insects can cause serious damage if left untreated—but with the right approach, they can be managed effectively.
The key is early identification, proper treatment, and ongoing maintenance.
By keeping your trees healthy and monitoring them regularly, you can prevent most pest problems before they become severe.
If you’re dealing with a persistent or serious infestation, it’s always best to seek expert advice. Professional arborists can diagnose the issue accurately and provide targeted solutions to protect your trees long-term.
Need Help with Tree Pests?
If your trees are showing signs of pest damage, don’t wait until it’s too late. The experienced team at AB Trees can assess the problem, recommend the right treatment, and help restore your trees to full health.
Contact AB Trees today for expert advice and reliable tree care services across Australia.
