Describe the spot before diagnosing it
Look at shape, colour, margin, texture and position. A dry bleached patch on the sunny side tells a different story from small lesions that multiply across several leaves. Note whether the spot begins at an edge, in the middle of the blade, near veins or at a previously injured point.
Do not use “fungus” as a synonym for spot. Some diseases cause leaf spots, but one photograph cannot reliably separate every environmental, bacterial, fungal or physical cause.
1. Environmental injury
Strong sun, very low temperatures near glass, cold draughts or localised heat can damage precise areas of a leaf. The relationship to position is often useful: damage on the window side, appearance after a move, or tissue affected immediately after a temperature event.
Compare with light for indoor plants.
2. Water and roots
A struggling root system can produce less specific foliage changes, including browning. Check whether the mix stays saturated, whether the pot drains and whether yellowing or wilting occurs as well. Do not label every spot “root rot” without examining the roots.
If spots coincide with constantly wet mix, review watering and potting mix.
3. Physical damage
A leaf that was folded, scratched, crushed or previously wounded can develop brown tissue at the injury site. The area often remains consistent with the original damage instead of new spots appearing repeatedly on different leaves.
4. Pests and feeding damage
Some pests create stippling, discoloured areas or secondary necrosis. Check undersides, new growth and leaf axils for insects, fine webbing, sticky residue or speckled patterns.
Identify the organism before treating; unnecessary sprays can themselves injure foliage.
5. When to consider an infectious leaf problem
Lesions that increase in number, spread across several leaves and appear favoured by prolonged leaf wetness or poor air movement deserve more caution. Some fungal or bacterial leaf spots can have halos, defined margins or water-soaked tissue, but appearance varies with host and pathogen.
The Missouri Botanical Garden's English ivy leaf-spot guide shows how bacterial and fungal patterns can differ and includes cultural steps such as removing infected tissue and reducing prolonged leaf wetness. Do not automatically extend that specific diagnosis to another species.
What to do while you observe the progression
- Photograph the whole plant and representative spots.
- Avoid keeping foliage wet for long periods unless the species specifically requires it.
- Provide reasonable air movement without extreme draughts.
- Temporarily isolate the plant if a contagious problem or pest is plausible.
- Remove heavily affected tissue with clean tools when appropriate for a confirmed problem.
- Avoid fungicides or other pesticides without a reasonable diagnosis, and always follow the product label.
Useful patterns
| Pattern | What to check |
|---|---|
| Dry patch on sunny side | Moves, exposure and heat |
| Spot exactly at a fold | Mechanical damage |
| Many new lesions on several leaves | Pests, leaf wetness, air movement, possible disease |
| Spots + saturated mix + wilting | Roots and drainage |
| Fine widespread stippling | Leaf undersides and pests |
The speed of spread is useful data
A sequence of photos shows whether one old lesion is stable or new spots are appearing on other leaves. That can help separate past injury from an active problem.
Return to the houseplant problems hub or compare dry and brown leaves.
Sources and further reading
General reference: RHS — Leaf damage on houseplants. Example of differences between fungal and bacterial leaf spots: Missouri Botanical Garden — leaf spots of English ivy.
Rapidly spreading lesions may warrant direct diagnosis rather than image comparison alone.