Guides
What are these spots on my plant leaves?
Leaf spots can come from disease, watering, scorch, cold or pests. In mild damp summers, fungal and bacterial spots are common. In hot dry weather, check scorch and watering first.
Check the edge of one spot
A clean rim, where dead tissue stops and green begins, often points to disease. An edge that fades into the surrounding leaf points more often to scorch, cold or watering. If the spot is raised, fuzzy or powdery, run a fingertip over it before deciding.
Work down the list
Fungal leaf spot
- What you would see
- Round brown, black or purple spots with a defined edge, sometimes with a yellow halo, spreading through a wet summer and worst on the lower leaves.
- The check
- Look at the centre of an older spot through a hand lens. A scatter of tiny black pinpricks points to a fungal leaf spot.
Bacterial leaf spot
- What you would see
- Angular spots with straight sides, arranged between the leaf veins, often on beans, tomatoes or brassicas.
- The check
- Hold the leaf up to the light. A wet, greasy, half-translucent ring at the margin of each spot is bacterial, and it means keeping off the plants while they are wet.
Rose black spot
- What you would see
- Dark blotches with a fringed, feathery edge running out into the green, on a rose, with the leaves yellowing around them and falling by August.
- The check
- Check what the plant is. On a rose, a spot with a ragged edge is usually black spot.
Overwatering or root rot
- What you would see
- Soft dark brown or black patches on a houseplant, often starting at the leaf base or spreading from the stem, with no defined rim, on compost that has stayed wet.
- The check
- Push a finger into the compost, then lift the plant out. Wet compost and brown, soft roots mean the spots are linked to root damage below.
Sun scorch or a cold night
- What you would see
- Large pale, bleached or papery patches on the leaves most exposed to a window, or sunken brown areas that appeared within a day or two and then stopped spreading.
- The check
- Ask whether it is getting worse. Scorch and cold damage happen once, so the marks stay as they are. A disease adds new spots.
Rust
- What you would see
- Small raised pustules, bright orange, brown or almost black, mostly on the undersides of the leaves, with pale dots showing through on top.
- The check
- Rub one with a fingertip. Coloured powder coming away on your finger is rust, and a flat spot that leaves nothing behind is not.
Sap-sucking pests
- What you would see
- Fine pale stippling rather than separate spots, sometimes with a silvery sheen, and small dark specks of excrement on the surface.
- The check
- Turn the leaf over and use a lens. Webbing at the shoot tips is red spider mite, and dark slivers that run when disturbed are thrips.
Blight
- What you would see
- Large dark brown or black patches spreading fast from the leaf tips and margins in a wet July or August, on potatoes or outdoor tomatoes, with the stems blackening too.
- The check
- Check the weather and the speed. Blight can collapse a plant in under a fortnight after two warm humid nights. Leaf spot is usually slower.
A virus
- What you would see
- Mottling, ring patterns or pale blotches following no clear outline, on new growth as well as old, often with distorted or puckered leaves.
- The check
- Look for a pattern instead of a dead spot. Mosaic and ringspot symptoms have no dead tissue in them; the leaf is discoloured rather than damaged.
Hard water and mineral marks
- What you would see
- Pale chalky rings or crusted white deposits on the leaf surface of a houseplant, or brown speckling on plants misted with tap water in a hard-water area.
- The check
- Try rubbing the mark off with a damp cloth. A deposit sitting on the surface comes away, and a spot in the leaf tissue does not.
Still not sure which one it is? Photograph the leaf and compare it against the full library.