Leaf Spot (Fungal)
'Leaf spot' covers many fungi (and some bacteria) that produce discrete spots on foliage.
Leaf Spot (Fungal) at a glance
| Also known as | Black spot, fungal leaf spot, anthracnose |
|---|---|
| Affected parts | Leaves |
| Most at risk | Many broadleaf species in wet, humid, stagnant conditions |
| Main cause | Leaf-spot fungi spreading in persistently wet/humid conditions |
| Severity | Usually cosmetic–moderate; heavy spotting causes early leaf drop |
| Reversible? | Manageable; protect new growth |
What to look for
- Leaves: Rounded brown, black, tan, or purplish spots, often with a yellow halo or a darker margin; spots may have tiny dots (fruiting bodies) in the centre; spots enlarge and merge into blotches; affected leaves yellow and drop early. Anthracnose follows veins as angular dark blotches.
- Whole tree: Worst on older/lower and shaded leaves and in wet spells; fallen spotted leaves around the base.
Overview
'Leaf spot' covers many fungi (and some bacteria) that produce discrete spots on foliage. Spores spread in water — rain, overhead watering, splashing — and germinate on leaves that stay wet, so the disease flares in warm, humid, stagnant, or over-watered conditions. It's rarely fatal but disfigures foliage and, when heavy, causes premature leaf drop that weakens the tree.
Causes
Prolonged leaf wetness; overhead watering; humid, crowded, low-airflow conditions; splashing spores from infected fallen leaves; and soft, dense growth.
Commonly confused with
Leaf scorch is diffuse edge/tip browning without defined spots or halos. Spider-mite stippling is fine speckling. Rust makes raised orange/brown pustules (usually on the underside). Nutrient/edema marks lack the spreading, haloed spots of fungal infection.
Which species are affected
Many broadleaf species (maples, oaks, elms, fruiting trees, photinia-relatives, etc.); worse on shaded, wet, crowded plants.
Treatment
Remove and bin affected and fallen leaves (don't compost); improve airflow and light; water at the soil, not over the foliage, and not late in the day. Apply a suitable fungicide (copper or a broad-spectrum product) to protect new growth, repeating per label through the wet season. Sanitise tools.
Prevention
Keep foliage dry (water the soil, morning watering), give good airflow and spacing, clear fallen leaves, avoid overhead watering, and don't crowd trees.