Rex begonia pests, webbing or sticky leaves: causes and what to do
6 results in the diagnosis tree begin with pests, 5 of them marked likely when the answers fit. They are ordered here for Rex begonia (Begonia rex), using what its sources say about pests and diseases and humidity and 6 problems recorded for it.
Sources last read 14 September 2026.
Begonia rex, the king begonia, fancy-leaf begonia, or painted-leaf begonia is a species of flowering plant in the family Begoniaceae. It is a rhizomatous begonia first brought to England from Assam, and documented in 1857. Wikipedia, CC BY-SA 4.0
Native range: S. Bhutan to N. Myanmar (subtropical). Also sold as fan plant and painted-leaf begonia.
What Rex begonia’s sources say that bears on this
- Pests and diseases
- Can be troubled by aphids, vine weevil, thrips, tarsonemid mite, mealybugs and caterpillars. Diseases: rhizome rot, stem rot, powdery mildews and grey moulds.RHS · read 13 September 2026
- Humidity
- ASHRAE recommends indoor relative humidity between 30% and 60%Penn State Extension · read 13 September 2026
How this shows up on a Rex begonia
Clusters of small soft insects on the shoot tips and buds: aphids
Aphids gather on the undersides of new leaves and around buds on the rex begonia, leaving honeydew and shed skins behind.
RHS lists aphids among the pests it may attract. Colonies build within days on young shoots, and the honeydew they shed makes the leaves sticky.
Telling it apart: Whether you can see them. Aphids are visible to the eye; the mites that distort new growth are not.
RHS · read 13 September 2026Holes chewed in the leaves, with droppings: a caterpillar pest
The rex begonia loses leaf tissue quickly. Caterpillars hide on the undersides or inside rolled leaves.
RHS lists caterpillars among the pests it may attract. They grow fast and eat more as they grow, so damage accelerates.
Telling it apart: Droppings. Caterpillars leave dark pellets below the damage; slugs leave slime.
RHS · read 13 September 2026Silver-flecked leaves and marked or distorted flowers: an insect pest
Patches of the rex begonia turn silver-gray, with black specks of excrement, and new growth may be scarred.
RHS lists thrips among the pests it may attract. They rasp the surface cells and drink the contents, which leaves the silvered, empty tissue.
Telling it apart: The black specks. Silvering with black dots is thrips; pale dots without them point at mites.
RHS · read 13 September 2026Small white woolly insects tucked into the leaf joints
Look into the tightest angles of the crown: white woolly patches there are mealybug colonies, often with a sticky sheen on the leaves below them.
RHS lists mealybugs among the pests it may attract. They feed on sap and shed the excess as sticky honeydew, and a colony tucked into the joints spreads before it is noticed.
Telling it apart: Wipe a tuft with a cotton swab. An insect smears or crawls; a mineral deposit or a hair does not.
RHS · read 13 September 2026Sudden wilting from a root pest: vine weevil grubs in the potting mix
Irregular notches appear along the edges of the leaves of the rex begonia, bitten at night by adult weevils; later the plant may wilt as grubs eat the roots.
RHS lists vine weevil among the pests it may attract. The adults feed at night and hide by day, so the notched edges are often the only sign above ground.
Telling it apart: Whether the plant is loose. Grub damage leaves a plant that lifts from its pot with few roots.
RHS · read 13 September 2026Twisted, stunted new growth and buds that fail: a mite pest
The newest leaves of the rex begonia emerge small, cupped and brittle, and buds stall or open misshapen. Older growth looks normal.
RHS lists tarsonemid mites (broad and cyclamen mites) among the pests it may attract. Feeding on unopened growth deforms it permanently, so the damage is locked in before it is seen.
Telling it apart: The texture of new leaves. Brittle, thickened growth points at mites; soft, curled growth with insects on it points at aphids.
RHS · read 13 September 2026Possible causes, likeliest first for a Rex begonia
Most likely mealybugs
Ranked higher because Rex begonia's recorded problems point this way.
- Small white woolly insects tucked into the leaf joints RHS
Why: Mealybugs are soft insects that cover themselves in white wax, which gives the cottony look.
What to try:
- Move the rex begonia away from other plants.
- Wipe off every insect you can see with a cotton swab dipped in rubbing alcohol, testing a single leaf first.
What would settle it: Touch a tuft with a cotton swab. If a small, pale, oval insect is underneath, it is a mealybug.
Most likely aphids
Ranked higher because Rex begonia's recorded problems point this way.
- Clusters of small soft insects on the shoot tips and buds: aphids RHS
Why: Aphids cluster on soft new growth and flower buds, where the sap is easiest to reach.
What to try:
- Rub them off with fingers, or rinse them off in a sink or shower.
- Repeat every few days while new ones appear.
What would settle it: Look for the pale shed skins among the insects. Aphids molt as they grow, and the skins are left behind in the colony.
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 rex 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 Rex begonia, still possible
Questions
- What usually causes pests on a Rex begonia?
- For Rex begonia: mealybugs, aphids and spider mites.
- How can I tell which one it is on my Rex begonia?
- What can you see? Fine webbing, and tiny pale speckles on the leaves; White, cottony tufts in the leaf joints; Small brown or pale bumps on stems and leaves that do not move; Clusters of small, soft insects on the new growth; Tiny dark flies around the soil; Sticky, shiny residue, but no insect I can see.
- What do Rex begonia's sources say about its pests and diseases?
- RHS: Can be troubled by aphids, vine weevil, thrips, tarsonemid mite, mealybugs and caterpillars. Diseases: rhizome rot, stem rot, powdery mildews and grey moulds.
- What does this look like on a Rex begonia?
- Aphids gather on the undersides of new leaves and around buds on the rex begonia, leaving honeydew and shed skins behind. Telling it apart: Whether you can see them. Aphids are visible to the eye; the mites that distort new growth are not.
- Is Rex 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 pests
Polka dot begoniaIrregular notches bitten from leaf edges by an insect pest
AlocasiaFine pale speckling on the leaves, then webbing at the tips: spider mites
Aloe veraSticky leaves and immobile shell-like insects on the stems
Areca palmDull, finely mottled fronds and faint webs: spider mites
Arrowhead plantCurled, sticky new leaf blades with green or black insects: aphids
Asparagus fernCurled, sticky new fronds with green or black insects: aphids
Something else wrong with the Rex 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.