Fungus on Crepe Myrtle Bark: Disease Pictures, Symptoms and Treatment for Australian Gardens
Crepe myrtles (Lagerstroemia indica and hybrids) are beloved in Australian gardens for their stunning summer blooms, vibrant autumn colour and attractive peeling bark. However, fungus on the bark can mar their beauty and threaten plant health. In humid subtropical regions like Queensland and northern New South Wales, or even during wet summers in southern states, bark fungal diseases are common. This guide covers the main culprits – with descriptive pictures – symptoms, causes tailored to Australian conditions, and proven control methods.
If you’ve noticed black sooty coatings, sunken lesions or dieback on your crepe myrtle’s bark, read on. Early identification and action can save your tree.
Common Fungus Bark Crepe Myrtle Diseases
Australian gardeners often encounter three key fungal issues on crepe myrtle bark: sooty mould, anthracnose and canker diseases like Botryosphaeria. Each has distinct symptoms, but all thrive in warm, humid conditions with poor airflow.
1. Sooty Mould (Capnodium spp. and similar fungi)
Symptoms: This is the most widespread ‘fungus bark crepe myrtle disease’. It appears as a black, velvety or sooty coating on bark, stems and branches, often starting after insect infestations. Leaves may also be affected, turning sooty and sticky. No direct tissue damage, but it blocks photosynthesis and looks unsightly.
Picture description: Imagine a close-up of mature bark with its natural mottled cinnamon tones covered in a thick, charcoal-black film that rubs off like soot on your fingers. In advanced cases, entire trunks glisten with a glossy black layer under dew. (Placeholder for image: (Sooty mould on crepe myrtle bark) – shows 10 cm section of trunk with heavy black coating.)
Australian context: Common in humid coastal areas (e.g., Brisbane to Sydney) during wet summers. It’s secondary to sap-sucking pests like aphids, scale or whitefly, whose honeydew feeds the fungus.
2. Anthracnose (Colletotrichum gloeosporioides)
Symptoms: Dark brown to black sunken lesions on young twigs and bark, often with pinkish spore masses in wet weather. Twigs die back, bark splits, and flowers may be spotted. Severe infections cause defoliation.
Picture description: A split-image: left shows smooth greyish bark with irregular 2-5 cm oval lesions, edges raised and centres sunken; right reveals orange-pink spores oozing after rain. (Placeholder: (Anthracnose lesions on crepe myrtle bark) – macro shot highlighting spore production.)
Australian context: Prevalent in high-rainfall tropics (north QLD) and irrigated gardens in drier areas like Perth. Favours overhead watering and dense canopies.
3. Canker Diseases (Botryosphaeria dothidea and similar)
Symptoms: Sunken, discoloured bark patches that crack and ooze amber sap. Branches wilt suddenly (dieback), with blackened vascular tissue under bark. Bark peels prematurely in irregular strips.
Picture description: Trunk cross-section: healthy beige bark contrasts with dark brown, cracked canker 15 cm long; inset shows scraped bark revealing black streaks in wood. (Placeholder: (Botryosphaeria canker on crepe myrtle) – before/after pruning shot.)
Australian context: Stress-related, hitting drought-stressed trees in variable climates like Melbourne or Adelaide after hot, dry spells followed by rain. Common on older trees over 10 years.
Fungus Bark Crepe Myrtle Disease Pictures Gallery
Visual identification is key. Here’s what to look for:
- Sooty mould: (Heavy sooty mould coating) – Trunk fully blackened, 20 cm span.
- Anthracnose early stage: (Small lesions) – Tiny brown spots merging.
- Advanced anthracnose: (Spore masses) – Pink ooze on wet bark.
- Botryosphaeria canker: (Sunken crack) – 30 cm vertical split with sap.
- Mixed infection: (Combined sooty & canker) – Sooty overlay on cankered bark.
Compare these to healthy bark: smooth, multi-coloured flakes without discolouration or ooze.
Causes and Risk Factors in Australian Gardens
Crepe myrtles prefer full sun, well-drained soil and low humidity, but Australia’s diverse climates pose challenges:
- Humidity and rainfall: Subtropical downpours (e.g., 1000+ mm/year in QLD) splash spores onto bark.
- Pest links: 80% of sooty mould cases trace to crepe myrtle aphids (Sarucallis kahawaluokalani), peaking October-February.
- Stress factors: Waterlogging in clay soils (common in Sydney basin), root damage from mowers, or drought in inland NSW/VIC.
- Planting issues: Crowded specimens (under 3 m spacing) trap moisture; mulch too close to trunk promotes rot.
Susceptible varieties include old-fashioned L. indica like ‘Sioux’; newer hybrids like ‘Acoma’ or ‘Natchez’ show better resistance.
Prevention Strategies for Australian Conditions
Prevention beats cure. Implement these year-round:
- Site selection: Plant in full sun (6+ hours/day), on mounds in heavy soils. Space 4-6 m apart for air flow.
- Pruning: Prune in late winter (July-August) to open the canopy. Remove crossing branches and thin to 5-7 main trunks. Sterilise secateurs with alcohol between cuts.
- Watering: Deep water (20-30 L/week in summer) at base, not overhead. Mulch 10 cm deep, 15 cm from trunk.
- Pest monitoring: Check undersides of leaves weekly for aphids/scale. Introduce ladybirds or use eco-oil sprays.
- Soil health: Test pH (ideal 5.5-6.5); add gypsum to sodic clays. Avoid high-nitrogen fertilisers that promote soft growth.
In high-risk humid zones, plant grafted cultivars from Australian nurseries like NuCizia.
Treatment Options: Safe and Effective for Aussies
Act fast at first signs. Always check APVMA labels for crepe myrtle use.
Cultural Controls (First Line)
- Scrape off sooty mould gently with a soft brush; it often fades as pests are controlled.
- Prune affected twigs 10-15 cm below symptoms, dispose in council green waste (don’t compost).
Organic Treatments
- Neem oil or eco-oil: Weekly sprays for pest-fungus cycle. Mix 20 mL/L water, apply evenings.
- Baking soda spray: 1 tsp bicarbonate soda + 1 mL detergent/L water; weekly for mild anthracnose.
- Milk spray: 1 part milk to 9 parts water; antifungal proteins help against sooty mould.
Chemical Fungicides (If Needed)
Use only if >30% bark affected:
- Copper oxychloride: For anthracnose/cankers. Spray at bud swell (September) and after rain; 20 g/10 L.
- Mancozeb: Broad-spectrum for sooty mould/anthracnose. Two applications, 14 days apart.
- Systemic options: Propiconazole for cankers (registered brands like Banol). Apply as soil drench in autumn.
Timing: Pre-emptive sprays in spring (September-November) in wet areas. Rotate chemicals to avoid resistance.
| Disease | Best Treatment | Application Frequency |
|---|---|---|
| Sooty Mould | Eco-oil + brush | Weekly until clean |
| Anthracnose | Copper spray | Every 14 days, 3x |
| Canker | Prune + propiconazole | Once, then monitor |
Recovery and Long-Term Care
Post-treatment:
- Fertilise sparingly: NPK 8-12-8 slow-release in spring (100 g/m²).
- Monitor for 6 months; healthy trees recover fully.
- Boost vigour: Top-dress with compost annually.
In severe cases (e.g., girdling cankers), remove the tree to prevent spread. Replace with resistant varieties like ‘Dynamite’ or ‘Zuni’.
When to Call a Professional
Seek an arborist if:
- Dieback exceeds 50% canopy.
- Trunk girth >30 cm with deep cankers.
- Suspect root rot (mushy base).
Local services via Gardening Australia or state ag departments offer diagnostics.
Crepe myrtles are tough in Aussie conditions – with vigilance, your tree can thrive fungus-free. Spot fungus bark crepe myrtle disease early using these pictures and tips, and enjoy those spectacular blooms.
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