Diagnose by symptom
Brown spots on leaves
Dark, brown or black spots are usually fungal diseases. Depending on the plant and spot shape, it may be:
Diseases
Alternaria leaf spot (early blight)
Brown to dark-brown spots appear on the leaves with characteristic concentric, zoned rings resembling a "target board", …
DiseaseAnthracnose
Dark, sharply defined, sunken spots appear on the leaves, stems and fruit, with collapsed, rotting patches on the fruit.…
DiseaseApple scab
Olive-green, velvety, blurred spots appear on the leaves and gradually darken and turn brown; heavily infected leaves tu…
DiseaseBrown rot (Monilinia)
On pome and stone fruit, brown, enlarging rot spots appear, on which concentrically arranged, grey-beige cushions of spo…
DiseaseTar spot of maple
The disease affects maples, especially Norway maple and sycamore maple. In summer, large, round, raised, glossy black sp…
DiseasePotato and tomato late blight
Dark-brown, spreading spots on the leaves (often with a lighter margin and a whitish coating on the underside in humid c…
DiseasePeach leaf curl
In spring the young leaves become puckered, thickened and curled, taking on a red or yellow-green colour with blistered …
Frequently asked questions
What causes brown spots on leaves?
Most often these are fungal leaf spots such as alternaria or septoria, giving brown spots often with a lighter centre or yellow halo. Brown spots also come from sunscald (dry, pale-brown patches on the light-facing side) and from watering with hard, limey water. The pattern and shape of the spots plus growing conditions point to the cause.
Are brown spots always a fungal disease?
No – fungal diseases (alternaria, septoria) usually cause numerous rounded spots that enlarge and may show concentric rings or tiny black fruiting bodies. Non-infectious spots, e.g. from sun, dry air or fertiliser, are more uniform and do not spread to neighbouring plants. If spots multiply quickly and spread, the cause is more likely fungal.
How do I limit fungal brown leaf spots?
Remove and discard infected leaves rather than composting them, and water at the base to avoid wetting the foliage. Give plants spacing and air movement so leaves dry quickly, since fungi need moisture to infect. For recurring problems, a contact fungicide can be applied according to the label.