Wax 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 Wax begonia (Begonia semperflorens), using what its sources say about light, soil moisture, humidity and pests and diseases and 2 problems recorded for it.
Sources last read 18 September 2026.
Native range: S. Brazil to NE. Argentina (seasonally dry tropical). Also sold as bedding begonia.
What Wax begonia’s sources say that bears on this
- Light
- Full shade, 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 Wax begonia
Fuzzy gray growth over spreading patches on leaves and stems
Damaged or dying tissue on the wax begonia is covered in gray, fuzzy growth, and the rot spreads into healthy parts.
RHS lists gray mold among the diseases it may get. Crowding and damp air around the plant let spores settle and grow.
Telling it apart: Where it starts. Botrytis begins on damaged or dying tissue; mildew starts on healthy leaves.
RHS · read 13 September 2026White, powdery patches on the leaves
The wax begonia develops a powdery white coating on its leaves and young shoots, starting as small spots.
RHS lists powdery mildew among the diseases it may get. The spores need no water on the leaf to infect it, which is why it appears indoors.
Telling it apart: Rub it. Powdery mildew wipes off like flour; mineral deposits from hard water stay.
RHS · read 13 September 2026Possible causes, likeliest first for a Wax begonia
Most likely powdery mildew
Ranked higher because Wax begonia's recorded problems point this way.
- White, powdery patches on the leaves 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 wax 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 spider mites
Why: Spider mites feed on individual leaf cells, and each emptied cell shows as a pale speck.
What to try:
- Move the wax 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.
Most likely thrips
Why: Thrips rasp the leaf surface and drink what leaks out, which leaves silvery, papery streaks.
What to try:
- Move the wax begonia away from other plants.
- Wash the leaves thoroughly and remove badly damaged ones.
What would settle it: Tap a leaf over white paper. Thrips are slender, fast-moving and about the size of a comma; they are easy to see once they are on paper.
Less likely for a Wax begonia, still possible
Questions
- What usually causes spots on the leaves on a Wax begonia?
- For Wax begonia: powdery mildew, spider mites and thrips.
- How can I tell which one it is on my Wax 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 Wax begonia's sources say about its light?
- RHS: Full shade, Partial shade.
- What does this look like on a Wax begonia?
- Damaged or dying tissue on the wax begonia is covered in gray, fuzzy growth, and the rot spreads into healthy parts. Telling it apart: Where it starts. Botrytis begins on damaged or dying tissue; mildew starts on healthy leaves.
- Is Wax 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
African violetFuzzy gray growth over spreading patches on leaves and stems
Barberton daisyDark spots with a yellow halo spreading across the leaves
Bearded irisFuzzy gray growth over spreading patches on leaves and stems
Bigleaf hydrangeaBrown or black spots on the leaves that grow and merge
Blue passion flowerBleached patches on the side facing the glass
Busy LizzieAngular pale patches and a downy coating on the undersides
Something else wrong with the Wax 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.