Brown spots on leaves: check the pattern and the spread.
Brown spots can result from environmental damage, pests or infection. Their appearance alone may not distinguish those causes. Notice which leaves are affected, whether spots are growing, and what changed before the damage appeared.
Updated
A spot is a clue, not a pathogen name.
Damage on the exposed side
A patch after a move into stronger sun can fit scorch. Check which surface faced the light and whether unexposed leaves are affected too.
Small marks with pest evidence
Inspect undersides for insects, webbing or residue. Visible pests and their feeding pattern are more useful than the spot color alone.
Spots that enlarge or multiply
Some leaf infections cause expanding lesions. Photograph the same leaves over time and keep the plant apart from others while you investigate.
Soft or water-soaked areas
Some bacterial diseases produce watery or collapsing tissue. Other injuries can look similar, so avoid naming an infection from a photo alone.
What to do today
- Check recent changes. A new window, a cold journey or a spray product may explain when the damage started.
- Look on both sides. Take a close-up with the boundary between affected and unaffected tissue in focus.
- Reduce spread while uncertain. Keep a potentially infected plant separate. Avoid splashing water from affected foliage to neighboring plants.
Maryland Extension explains the overlapping appearances of fungal leaf spots and bacterial leaf spots. Their recommendations depend on the cause; a general “brown spot” treatment is not a reliable substitute.
When an expert helps
Seek an in-person assessment if damage spreads quickly, the stem becomes soft, several plants are affected or the plant is valuable. Take clear photos and a short history of watering and recent changes. Do not apply a pesticide merely because a spot looks fungal.
Brown-spot questions
Should I remove every spotted leaf?
Removing badly affected tissue may be appropriate for some problems, but not every mark is infectious. Identify the likely cause and avoid removing most of the plant’s working leaves on appearance alone.
Can Plant Doctor identify the fungus?
Plant Doctor can suggest likely explanations from visible evidence. Photos cannot reliably confirm every pathogen. A plant clinic or diagnostic service may need a sample to determine the cause.
Sources and further reading
Care guidance checked against the sources below. Plant Doctor’s app examples are separate from these references; the institutions do not endorse the app.
- University of Maryland Extension — fungal leaf spots
- University of Maryland Extension — bacterial leaf spots
- Royal Horticultural Society — leaf damage on houseplants
This guide offers general plant-care information. A photo cannot confirm every cause; a local nursery or extension service can help with severe or unclear cases.