Powdery Mildew on african violet
What's Happening
Powdery mildew (Oidium or Erysiphe species) infects African violet leaves when humidity exceeds 60% combined with poor air circulation. Unlike other fungi, powdery mildew thrives on dry leaf surfaces but requires high atmospheric humidity - the paradoxical conditions common in indoor growing. The fuzzy leaf trichomes trap moisture and spores, creating ideal microhabitats for fungal establishment. Spores overwinter in contaminated soil and pots, reinfecting even properly treated plants. Cool temperatures (below 65°F/18°C) exacerbate the problem by slowing the plant's natural defense responses while not affecting fungal growth.
How to Fix It
- 1
Isolate immediately: Move affected plant away from others to prevent spore spread
- 2
Remove infected tissue: Cut away all leaves showing white powdery patches using sterilized scissors
- 3
Clean thoroughly: Wipe remaining leaves with damp cloth to remove surface spores; do not wet crown
- 4
Repot with sterile soil: Discard old soil completely; scrub pot with 10% bleach solution
- 5
Apply treatment: Mix 1 tbsp baking soda + 1/2 tsp liquid soap in 1 gallon water; spray leaves top and bottom weekly until clear
- 6
Improve airflow: Place small fan near plants on low setting to increase circulation
- 7
Switch to bottom watering: Prevents splashing spores onto leaves
How to Prevent It
Maintain 40-60% humidity with pebble trays (avoid leaf wetting); ensure good air circulation via fan; space plants 6+ inches apart; sterilize all tools and pots; quarantine new plants for 2 weeks; apply preventative neem oil spray every 2 weeks during high-humidity months