Powdery mildew on rex begonia
How do I treat powdery mildew?
On rex begonia: A dusty white coating that wipes off the upper leaf surface. It thrives in still air rather than on wet leaves, so space the plants apart and improve airflow first.
A dusty white coating on the upper leaf surface that looks like talc and wipes off, leaving yellowed tissue underneath. Unlike most fungal problems it thrives in dry air with poor circulation rather than wet leaves.
Why this plant gets them
it prefers 50% humidity and still air suits the fungus better than it suits the plant — crowding is usually the real cause.
Drawn from this species' own record — humidity floor 50%, watering every 5–10 days, clumping habit. Full care entry.
The life cycle, and why one treatment fails
A fungus rather than an insect. Spores are essentially always present and only establish when air is still and humidity is moderate. Crowded plants and a room with no airflow are the conditions it needs.
What actually clears them
Remove affected leaves and bin them rather than composting. Improve airflow — spacing the plants apart or a small fan does more than any spray. A potassium bicarbonate solution or a proprietary fungicide handles what remains.
Misting, which makes it worse. Moving the plant somewhere darker, which slows the plant more than the fungus. Milk sprays, which have some evidence outdoors and little indoors.
Other pests recorded for this species
- Mealybugs this week
- Thrips act today
- Spider mites act today
Is it a pest at all?
Plenty of what looks like pest damage is a care problem. If you cannot actually find the insect described above, check the diagnosis pages for this species instead — brown crispy edges, leaf drop — where the causes are ranked for this plant specifically.
Powdery mildew on other species here
1 other species in this database have powdery mildew recorded against them. The treatment is the same; only the reason they are prone differs.
- Polka dot begonia Begoniaceae
Sources
- Missouri Botanical Garden Plant Finder — Begonia rex Pest and disease record for this species. Checked 2026-09-12.
- North Carolina Extension Gardener Plant Toolbox — Begonia rex Extension pest guidance.
- Royal Botanic Gardens Kew, Plants of the World Online — Begonia rex Accepted name and family. Checked 2026-09-12.
- This database's own care record for Begonia rex — the humidity, watering and habit fields this page reasons from.
Compiled and edited by Tony Valcarcel · 2026-09-12
Treatment guidance is the standard approach for this pest and is not specific to
your plant's condition. If a plant is already collapsing, the pest may not be the
whole story. How this is sourced.