Polka dot begonia spots on leaves: causes and what to do
8 results in the diagnosis tree begin with spots on the leaves, 5 of them marked likely when the answers fit. They are ordered here for Polka dot begonia (Begonia maculata), using what its sources say about light, soil moisture, humidity and pests and diseases and 2 problems recorded for it.
Sources last read 14 September 2026.
Begonia maculata, the polka dot begonia, is a species of begonia native to southeast Brazil. It grows naturally in the understory of the Atlantic rainforest, with occurrences confirmed in the Brazilian states of Espírito Santo and Rio de Janeiro. Wikipedia, CC BY-SA 4.0
Native range: Brazil (Rio de Janeiro) (wet tropical). Also sold as trout begonia.
What Polka dot begonia’s sources say that bears on this
- Light
- Partial shadeRHS · read 13 September 2026
- Soil moisture
- Moist but well-drained or Well-drainedRHS · read 13 September 2026
- Humidity
- ASHRAE recommends indoor relative humidity between 30% and 60%Penn State Extension · read 13 September 2026
- Pests and diseases
- Can be troubled by aphids, vine weevil, greenhouse thrips, mites, mealybugs and caterpillars. Diseases: rhizome rot, stem rot, powdery mildews and grey moulds.RHS · read 13 September 2026
How this shows up on a Polka dot begonia
Fuzzy gray growth over spreading patches on leaves and stems
Soft, discolored patches on the leaf blades, stems or faded flowers of the polka dot begonia grow a gray fur that puffs dust when disturbed.
RHS lists gray mold among the diseases it may get. It thrives on spent flowers and fallen leaves left on the plant, and moves from there to living tissue.
Telling it apart: The fur. Gray mold carries a gray, dusty coat; a plain leaf spot does not.
RHS · read 13 September 2026Pale powdery spots that merge into a white film
The polka dot begonia develops a powdery white coating on its leaf blades and young shoots, starting as small spots.
RHS lists powdery mildew among the diseases it may get. The fungus grows on the leaf surface and spreads by airborne spores, most in still air around a plant whose roots are dry.
Telling it apart: Whether there are insects. Mildew is a film with nothing moving in it.
RHS · read 13 September 2026Possible causes, likeliest first for a Polka dot begonia
Most likely powdery mildew
Ranked higher because Polka dot begonia's recorded problems point this way.
- Pale powdery spots that merge into a white film RHS
Why: A white coating that wipes off is the surface growth of a fungus.
What to try:
- Remove the worst-affected leaves.
- Improve air movement around the polka dot begonia and space it away from others.
What would settle it: Wipe a patch. Powdery mildew comes away and leaves a yellowed patch beneath. White that does not wipe off is part of the leaf, or a mineral deposit from hard water.
Most likely cold
Ranked higher for Polka dot begonia because of what its sources say.
Its RHS hardiness rating puts this plant's cold floor at 10°C or above, so a cold windowsill at night is a strong explanation.
- H1B — 10–15°C RHS · read 13 September 2026
Why: Soft, dark patches rather than crisp ones are damaged tissue rather than dried tissue.
What to try:
- Move it away from the glass at night, or keep the curtain on the room side of the polka dot begonia.
- Leave damaged leaves until new growth appears, then remove the worst of them.
What would settle it: Where the polka dot begonia sits at night, and what the glass feels like at that hour. Damage that appeared after one cold night, on the side facing the window, is the pattern.
Most likely spider mites
Why: Spider mites feed on individual leaf cells, and each emptied cell shows as a pale speck.
What to try:
- Move the polka dot begonia away from other plants.
- Wash the leaves, top and underside, with a strong spray of water in a shower or sink.
What would settle it: Hold a sheet of white paper under a leaf and tap the leaf. Tiny specks that move across the paper are mites.
Less likely for a Polka dot begonia, still possible
Questions
- What usually causes spots on the leaves on a Polka dot begonia?
- For Polka dot begonia: powdery mildew, cold and spider mites.
- How can I tell which one it is on my Polka dot begonia?
- What do the marks look like? Pale, dry, bleached patches on the side facing the window; Brown or black spots, many with a yellow ring around them; Tiny pale speckles all over, sometimes with fine webbing underneath; A white powdery coating that wipes off; Silvery streaks with tiny black dots; Dark, soft, water-soaked patches.
- What do Polka dot begonia's sources say about its light?
- RHS: Partial shade.
- What does this look like on a Polka dot begonia?
- Soft, discolored patches on the leaf blades, stems or faded flowers of the polka dot begonia grow a gray fur that puffs dust when disturbed. Telling it apart: The fur. Gray mold carries a gray, dusty coat; a plain leaf spot does not.
- Is Polka dot begonia safe to handle while I check it?
- Its sources list it as toxic to cats and dogs. Wash your hands after handling the roots or sap, and keep trimmings away from pets.
Other plants that show spots on the leaves
Rex begoniaPale powdery spots that merge into a white film
Aloe veraWashed-out patches that do not spread to the shaded side
Areca palmWilting with white, waxy patches on the root ball: a root pest
Arrowhead plantBrown or black spots on the leaf blades that grow and merge
Chinese money plantWhite, powdery patches on the leaves
Chusan palmBleached patches on the side facing the glass
Something else wrong with the Polka dot begonia?
What this does not cover
This page orders a decision tree's results using a plant's sourced care. It has not seen your plant, its pot or its window, and two problems at once are common: that is the usual reason a confident answer turns out wrong. The questions in the diagnosis tool narrow it further than a list can.