Botrytis (Gray Mold) on Rex Begonia
Rex Begonia (Begonia rex)
Symptoms
- fuzzy gray mold
- brown mushy patches
- rapid spreading spots
- moldy smell
- collapsed leaf sections
Causes
Botrytis cinerea fungal infection
Botrytis is an aggressive fungal pathogen that thrives in cool, humid, poorly ventilated conditions — closely matching the environment many growers create for Rex Begonia. It typically infects damaged, dying, or very soft tissue first (a spent flower, a damaged leaf edge, a leaf touching wet soil) and can spread rapidly to healthy adjacent tissue from that entry point, producing a characteristic fuzzy gray-brown mold coating as it progresses.
Dead or dying plant material left in place
Spent flowers, yellowed leaves, or other decaying plant material left on or near the plant provide an ideal entry point and food source for Botrytis to establish before spreading to living tissue.
Cool temperatures combined with high humidity and stagnant air
Botrytis is notably more aggressive in cooler conditions than many other fungal pathogens, meaning a humid terrarium or growing space that also runs cool, particularly overnight, creates a especially favorable environment for infection.
How to Fix It
- 1
Act quickly, since Botrytis spreads faster than most other fungal issues on houseplants and can consume significant plant tissue within days if untreated.
- 2
Remove all visibly affected tissue immediately with sterile scissors, cutting into clearly healthy tissue beyond the visible mold to ensure the infection's full extent is removed.
- 3
Remove and dispose of all dead or dying plant material from the pot and growing area, including spent flowers and yellowed leaves, since these serve as ongoing infection sources.
- 4
Improve air circulation immediately and, if possible, avoid letting temperatures drop into the cooler range overnight, since both stagnant air and cool temperatures favor this specific pathogen.
- 5
Apply a fungicide labeled for Botrytis and safe for houseplants, following label directions, and repeat according to the product's recommended interval.
- 6
Isolate the plant from others sharing its growing space until the infection is fully resolved, since Botrytis spores spread readily through the air to nearby susceptible plants.
Prevention
- Promptly remove spent flowers and dead or yellowing leaves rather than letting them remain on the plant
- Ensure air circulation even in humidity-controlled growing spaces
- Avoid letting temperatures drop sharply overnight, particularly in combination with high humidity
- Water at the soil level to avoid leaving moisture sitting on leaves and stems
- Inspect regularly, since Botrytis spreads fast enough that early detection meaningfully changes treatment outcomes
Quick Summary
| Plant | Rex Begonia (Begonia rex) |
|---|---|
| Category | Disease |
| Likely causes | Botrytis cinerea fungal infection, Dead or dying plant material left in place, Cool temperatures combined with high humidity and stagnant air |
| Fix steps | 6 steps — see above |