Plant SOS · Symptoms
Spots appearing
on my leaves
Leaf spots can mean many different things — and that's precisely the problem. A black spot does not have the same cause as a white spot, and a dry brown spot is not treated like a wet brown spot. Color, texture, location, and speed of spread are the four key clues to identifying what's really going on.
In this guide, we provide a clear method for reading your spots, identifying the cause, and taking appropriate action. Because incorrect treatment can worsen the situation — especially if you confuse sunburn with a fungal disease.
Reading a spot: the method
Before treating, observe. Ask yourself these four questions:
1. What color is the spot? Black, brown, white, yellow, or discolored — each color points to a family of causes.
2. Is the spot dry or wet? A dry, crispy spot is often a burn or dehydration. A wet, soft spot or one surrounded by a yellow halo usually indicates an infection.
3. Where is it located? At the edge of the leaf, in the center, or evenly distributed? Edges suggest an environmental cause, the center an infection or pest.
4. Is it spreading rapidly? Rapid spread within a few days indicates an active infection that requires immediate action.
"The color of a spot is the first clue.
Its texture confirms the diagnosis."
1. Dry brown spots — burns
Sunburn or dehydration
Dry brown spots are the most common and least serious. They appear when the leaf has been exposed to too much direct sun or when the plant has temporarily lacked water. The spot is clear, dry to the touch, and generally does not spread.
2. Black or wet brown spots — fungal disease
Fungal or bacterial infection
Soft, dark spots, often surrounded by a yellow or watery halo, are a sign of a fungal or bacterial infection. They spread rapidly, especially in a humid and poorly ventilated environment. Some infections can kill a plant in a few weeks if left untreated.
3. White or powdery gray spots — powdery mildew
Fungus: powdery mildew
A white or powdery gray coating on the leaves is the signature of powdery mildew, a very common fungus that thrives when the air is warm, dry, and stagnant. Contrary to popular belief, powdery mildew prefers dry conditions — it is not a humidity-related disease.
4. Yellow spots with tiny dots — spider mites
Mites: spider mites
Small yellow or beige spots evenly distributed on the leaf blade, sometimes accompanied by fine webbing on the undersides of leaves, are the signature of spider mites. These microscopic mites suck sap from leaf cells, creating these characteristic discolorations. They thrive in dry, warm air.
5. Irregular light spots — virus or deficiency
Viral mosaic or mineral deficiency
Light, discolored spots, irregularly shaped and distributed without apparent logic, can indicate either a mineral deficiency (lack of magnesium or iron) or a viral infection transmitted by sap-sucking insects. Viruses cannot be treated — but deficiencies can.
⚠ Common mistake to avoid
Never treat sunburn with a fungicide — you would stress the plant for nothing. And do not confuse powdery mildew (white powder that rubs off) with lime deposits (hard white marks that do not rub off). The treatment is radically different.
Summary table — identify your spot
| Appearance | Texture | Probable cause | Urgency |
|---|---|---|---|
| Brown, sharp | Dry, crispy | Sunburn or dehydration | Low |
| Black or dark brown | Soft, wet, yellow halo | Fungal or bacterial disease | High |
| White or gray | Powdery, rubs off | Powdery mildew | Moderate |
| Yellow with fine dots | Dull blade, webbing | Spider mites | Moderate |
| Light, irregular | Neither dry nor wet | Virus or mineral deficiency | Low to moderate |
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Launch diagnosis🌿 Guide written by the Douceur Maison Plant SOS team.
We write practical guides to help enthusiasts care for their indoor plants. · sosplantes@douceurmaison.fr