Protecting Crepe Myrtles from Australian Pests

Crepe myrtles are remarkably pest-resistant compared to many ornamental trees, but they're not immune to insect problems. Australian gardens host several pest species that can affect crepe myrtle health and appearance, from sap-sucking insects that weaken growth to borers that attack trunks and branches. Understanding which pests to watch for and how to manage them helps you maintain healthy, beautiful trees.

The good news is that most pest problems on crepe myrtles are manageable without resorting to heavy chemical treatments. Healthy trees resist pest damage far better than stressed plants, so good cultural practices form the foundation of pest prevention. When intervention becomes necessary, targeted treatments minimise environmental impact while effectively controlling problem insects.

Aphids: The Most Common Pest

Crepe myrtle aphids (Tinocallis kahawaluokalani) are the most frequently encountered pest on these trees in Australia. Originally from Asia like the trees themselves, these small, pale yellow-green insects congregate on new growth during spring and early summer, sucking sap and weakening developing shoots and flower buds.

Identifying aphids is straightforward. Check the undersides of new leaves and growing tips where you'll find clusters of small, soft-bodied insects often attended by ants. Ants farm aphids for their honeydew secretions, so ant activity on your crepe myrtle often signals an aphid infestation even before you spot the aphids themselves.

Aphid damage includes distorted, curled new growth, reduced flowering from damaged buds, and the characteristic sticky honeydew coating leaves and any surfaces beneath the tree. This honeydew quickly develops sooty mould, a black fungal coating that while not directly harmful to the tree, is unsightly and reduces photosynthesis by blocking light to leaves.

Control options range from doing nothing to chemical treatment depending on infestation severity. Light aphid populations are often controlled naturally by predatory insects including ladybirds, lacewings, and hoverfly larvae. Encouraging these beneficial insects by avoiding broad-spectrum pesticides often provides sufficient control without intervention.

Scale Insects

Several scale species attack crepe myrtles in Australia, appearing as small, raised bumps on twigs, branches, and sometimes leaves. Scale insects are sap-suckers like aphids but remain stationary once they settle on the plant, protecting themselves beneath waxy or armoured coverings.

Soft scales are more common on crepe myrtles, appearing as oval, slightly domed bumps in shades of brown, tan, or grey. They produce honeydew like aphids, leading to sooty mould development. Hard or armoured scales produce protective coverings that remain after the insect dies, sometimes making it difficult to determine whether an infestation is active or historical.

Light scale populations cause minimal damage and may not require treatment. Heavy infestations weaken trees, reduce flowering, cause branch dieback, and make the tree more susceptible to other stresses. Scales often build up over several years, so early detection and management prevents more serious problems developing.

Horticultural oil applied during the dormant season smothers overwintering scales before they become active in spring. Timing is important: apply oil on a mild, dry day when temperatures will remain above 4°C for at least 24 hours after application. Summer oil formulations can be used on active scales during the growing season but require more careful application to avoid leaf damage.

For severe infestations, systemic insecticides containing imidacloprid provide effective control when applied as a soil drench in early spring. The tree absorbs the chemical and transports it to feeding sites where scales ingest it while feeding. This approach avoids spraying foliage but should be used thoughtfully due to potential impacts on pollinators and other beneficial insects.

Crepe Myrtle Bark Scale

Crepe myrtle bark scale (Acanthococcus lagerstroemiae) is a relatively recent arrival to Australia, first detected in 2020. This pest from Asia has devastated crepe myrtles in parts of the United States and poses a significant threat to Australian trees.

Unlike leaf and twig scales, bark scale settles primarily on trunks and major branches, appearing as white, felt-like encrustations that blacken the bark with heavy sooty mould growth. Females produce pink "blood" when crushed, providing definitive identification. Heavy infestations weaken trees significantly, reducing flowering and potentially killing branches or entire trees.

Report any suspected bark scale to your state or territory biosecurity authority, as surveillance and management efforts depend on knowing where this pest has established. Early detection and rapid response may limit spread before populations build to damaging levels.

Management follows similar principles to other scale insects: horticultural oils for contact control, systemic insecticides for severe infestations. The trunk location makes bark scale more accessible for targeted treatment but also means any sooty mould affects the ornamental bark display. Regular monitoring and early intervention are critical.

Boring Insects

Several boring insects can attack crepe myrtles, particularly trees weakened by drought, poor nutrition, or other stresses. Healthy, vigorous trees produce sap flows that drown or expel boring larvae, making them far less susceptible to attack.

Flathead borers are among the most common borers affecting crepe myrtles. Adult beetles lay eggs in bark crevices, and hatching larvae tunnel beneath the bark, feeding on the cambium layer. Signs include D-shaped exit holes, dying branches, and bark that separates from underlying wood when pressed. Severe infestations can girdle trunks, killing the tree above the damaged area.

Longicorn beetle larvae bore deeper into the wood, creating larger tunnels that weaken trunk and branch structure. Frass (sawdust-like boring waste) pushed from entry holes indicates active infestation. Longicorn damage can cause branches to break unexpectedly, creating safety hazards.

Prevention through good tree health is the primary defence against borers. Ensure adequate watering during drought, avoid wounding bark with equipment, and address any other stresses promptly. Trees rarely recover fully from severe borer damage, so prevention is far more effective than treatment.

If borer damage is detected early, cut out and destroy affected branches, making cuts well below visible damage to ensure complete removal. Severely affected trees may require removal to prevent borers spreading to other susceptible plants. Chemical trunk treatments provide some protection but work best preventatively rather than after infestation establishes.

Japanese Beetles

Japanese beetles (Popillia japonica) were detected in Melbourne's inner suburbs in 2023 and remain subject to eradication efforts. While not yet established across Australia, gardeners should understand this pest and report any sightings immediately.

Adult Japanese beetles are distinctive: metallic green bodies with copper-brown wing covers, approximately 10-15mm long. They feed on foliage, flowers, and fruit of over 300 plant species, including crepe myrtles. Feeding damage creates a characteristic "skeletonised" appearance where only leaf veins remain.

Larvae are C-shaped white grubs that live in soil, feeding on grass roots. Heavy lawn damage with easily lifted turf may indicate larval infestation. The complete lifecycle takes one year, with adults most active during summer.

Current detections are being actively managed by authorities, with intensive trapping and treatment programs in affected areas. Report any suspected Japanese beetles to your state biosecurity authority immediately. Include photos if possible and note the exact location. Do not attempt to manage suspected Japanese beetles yourself, as proper identification and coordinated response are essential.

Integrated Pest Management Approach

Effective pest management combines multiple strategies rather than relying solely on chemical treatments. This integrated approach produces better long-term results while minimising environmental impact and preserving beneficial insects.

Cultural practices form the foundation. Healthy trees resist pest damage better than stressed plants, so proper watering, appropriate fertilising, and correct pruning reduce susceptibility. Avoid over-fertilising with nitrogen, which promotes soft, succulent growth that attracts sap-sucking pests. Our fertilising guide details balanced nutrition approaches.

Biological control through encouraging natural predators provides ongoing pest suppression without chemical inputs. Avoid broad-spectrum insecticides that kill beneficial insects along with pests. Plant diverse gardens that support predatory insects throughout the year, and tolerate minor pest activity that serves as food for beneficial species.

Monitoring catches problems early when they're easiest to manage. Regularly inspect your crepe myrtle's new growth, undersides of leaves, bark, and branch crotches where pests often congregate. Early detection allows targeted treatment before populations explode.

Targeted treatment when necessary uses the least toxic effective option applied precisely where needed. Start with physical controls like water sprays and hand removal for small infestations. Progress to horticultural oils and soaps if needed. Reserve systemic insecticides for severe problems that don't respond to gentler approaches.

Preventing Future Problems

A proactive approach to pest prevention reduces the frequency and severity of infestations over time. Implementing preventive practices as part of your regular garden maintenance pays dividends in healthier, more attractive trees.

Select disease-resistant varieties when planting new crepe myrtles. Modern cultivars bred for Australian conditions often show improved pest and disease resistance compared to older varieties. Check our variety comparison tool for information on specific varieties and use our Variety Finder Quiz to match varieties to your conditions.

Maintain good garden hygiene by removing fallen leaves and pruned material promptly. Many pests overwinter in plant debris, emerging in spring to reinfest trees. Clean up thoroughly in autumn and dispose of infested material rather than composting it where pests might survive.

Quarantine new plants before adding them to your garden. Nursery stock sometimes carries pests that establish before you notice them. Keep new trees isolated for a few weeks, inspecting regularly for pest signs before planting near existing crepe myrtles.

By combining vigilant monitoring, good cultural practices, and thoughtful intervention when necessary, you can maintain healthy crepe myrtles largely free of serious pest problems. For guidance on disease issues that sometimes accompany or follow pest damage, see our disease prevention guide. Together, proper pest and disease management ensures your crepe myrtles provide years of spectacular summer colour.