Pests and diseases of forests and wood

Pests and diseases in forests

Keeping trees healthy and protecting them from pests and diseases is important to the long-term productivity of forests.

Being aware of the symptoms of Australia’s most common pests and diseases can help, as well as those exotic pests and diseases known to cause damage to forests overseas.

Common pests and diseases

Insect pests and fungal diseases can damage shoots, leaves and crowns, which can reduce tree growth and condition. If severe, the damage can cause trees to die. Insects and fungi can also reduce wood quality, resulting in lower yields and reduced timber prices.

Being able to recognise the symptoms of pests and diseases is critical for managing a healthy and productive forest.

Stem borers

Stem borers are grubs or caterpillars (moth or beetle larvae) that tunnel through and feed on wood, causing damage to twigs, branches, stems and trunks. Stem borers can reduce wood quality in harvested logs and timber.

Symptoms include the presence of sawdust (frass), damaged or lifted bark, exit holes, cracking, swelling, leaking sap, ring-barking (girdling) and withered branch tips.

Stem borers include:

Leaf-chewing insects

Leaf-chewing beetles and mites feed on tree foliage and can cause extensive damage, especially to young trees. Symptoms include jagged or ripped leaf edges, reduced leaf area, distortion and dieback in young leaves, and defoliation.

Leaf-chewing insects include:

Leaf miners and gallers

Leaf miners feed inside the leaf between the top and bottom surfaces. Symptoms include dried, silvery or brown leaf tissue. This can cause leaves to shed early and a severe infection can cause defoliation.

Gall-formers are small wasps or flies that lay eggs between the leaf surfaces where the hatched larvae feed. Symptoms include the tree developing galls, which are swellings in leaf or shoot tissue that surround the eggs and larvae, sometimes causing significant defoliation.

Leaf mining insects include:

Sap-sucking insects

These insects affect trees by removing large quantities of water and nutrients, causing wilted or shrivelled growing tips. Symptoms include leaf discolouration, leaf withering or in severe infestations, leaf loss.

Sap-sucking insects include:

Fungal diseases

A number of fungal diseases affect trees by infecting their leaves, stems, bark and roots. Leaf symptoms include spots, blotches, blisters, powder and changes in colour (discolouration). This can cause defoliation, particularly in the lower crown.

Symptoms of affected stems and branches include dying patches, bark stains, cracks and splits (sometimes with leaking sap) and sheets of fungal mycelium (dense strands of fungal threads) under the bark.

Fungal diseases include:

Exotic pests and diseases

Queensland's forests are vulnerable to exotic pests and diseases. If introduced, these could have an impact on the survival or growth of trees and the quality and value of the timber.

The risk of incursions by exotic pests and diseases continues with increasing globalisation of trade. Forest managers need to be aware of exotic pests and diseases, as early detection is essential to prevent these disease outbreaks from becoming established.

Exotic pests

Asian gypsy moth

The larvae of this moth (caterpillars or grubs) feed on many tree species including eucalypts and pines. Eggs and larvae are often found on timber and shipping containers and, if introduced to Australia, could cause significant damage to Queensland eucalypt and pine plantations.

Read about the Asian gypsy moth.

Cossid moths

Cossid moths are native to South Africa and South America, where they feed on both native and exotic trees. The feeding larvae can bore large galleries into the heartwood of living trees. Multiple galleries can weaken stems and cause them to break in strong winds. The tunnels also allow fungal rot and stains to enter.

Read about the cossid moth.

Pine wilt nematode

The pine wilt nematode is native to the United States and Canada and causes pine wilt disease. This has caused significant damage to forests in north-eastern Asia and Portugal. The nematode is carried by adult pine sawyer beetles that transmit the nematode while feeding on bark or twigs. Nematodes block the trees' water-carrying vessels, causing rapid wilting and tree death.

Read about the pine wilt nematode.

Exotic diseases

Myrtle rust

Myrtle rust has severely damaged eucalypt plantations in South America and may have a significant impact on managed eucalypt plantations in tropical and subtropical coastal regions of eastern Australia. This potentially damaging disease has also been found in some native Queensland trees.

Read about myrtle rust.

Coniothyrium stem canker

This is a serious stem disease of eucalypts. It has had a significant impact in South African plantations, affecting new growth and wood quality.

Read about coniothyrium stem canker.

Eucalypt leaf spot or blight

The fungus occurs in southern and South-East Asia and causes distortion and loss of leaves in eucalypts.

Read about eucalypt leaf spot.

Pitch pine canker

This disease may cause dieback or infected trees may die. It has caused significant damage to pine plantations in California.

Read about pitch pine canker.

Reporting pest and diseases

All Queenslanders have a ‘general biosecurity obligation’ under Queensland's Biosecurity Act 2014 (PDF, 1.5MB).

This means that individuals and organisations whose activities pose a biosecurity risks must:

  • take all reasonable and practical steps to prevent or minimise each biosecurity risk
  • minimise the likelihood of causing a ‘biosecurity event’, and limit the consequences if such an event is caused
  • prevent or minimise the harmful effects a risk could have, and not do anything that might make any harmful effects worse.

If you find an unusual pest or disease contact:

To report any suspected exotic plant pests and diseases, contact either:

Quarantine restrictions govern the movement of plants, soil and farm machinery to prevent diseases spreading from affected areas to unaffected areas.

Learn more about moving plants, plant products and related items, including quarantine restrictions and maps.

Resources for forest pests and diseases

The following online databases can help you identify pests and diseases: