⚠ ModerateErysiphe and Golovinomyces spp. form a superficial white mycelial coating on the adaxial leaf surface — visually resembling a fine white powder or crystalline dusting.
Powdery Mildew — Erysiphe & Golovinomyces spp.
Commonly affects: Begonia rex, Kalanchoe blossfeldiana, Ficus benjamina, Succulent varieties
A white to grey powdery coating appears on leaf surfaces, stems, and occasionally flower buds. Unlike other fungal diseases, powdery mildew grows on the surface rather than inside plant tissue, giving it a dusted-flour appearance. Affected tissue may yellow beneath the coating. Unlike downy mildew, it occurs on the upper leaf surface and does not require standing water — in fact, it thrives in dry conditions with high humidity.
Potential Causes
- 1High humidity combined with poor air circulation creating a boundary layer of stagnant moist air around foliage
- 2Overcrowded growing conditions preventing air movement between leaves
- 3Moderate temperatures (15–26°C) with fluctuating humidity — the classic greenhouse-window environment
- 4Weakened plants from nutrient stress, root issues, or extreme temperatures becoming more susceptible
Solution Steps
- 1Isolate the affected plant immediately and remove visibly infected leaves — place them directly into a sealed bag, not the compost.
- 2Prepare a baking soda spray: 1 tsp sodium bicarbonate, ½ tsp liquid castile soap, 1 litre water. Apply to all leaf surfaces — the alkaline pH disrupts spore germination.
- 3Alternatively, dilute apple cider vinegar (2 tbsp per litre of water) and apply as a foliar spray — acidity similarly inhibits mildew growth.
- 4For persistent infections, apply a registered sulphur-based fungicide according to label instructions.
- 5Improve air circulation around the plant using a small fan on low setting.
- 6Reduce leaf wetting during watering — water the substrate directly, never overhead.
Prevention Tip
A preventive spray of dilute potassium silicate (0.5 g/L) applied monthly strengthens cell walls and measurably reduces powdery mildew susceptibility. Silicon supplementation is particularly effective for Begonias, which are chronically prone.
Related Issues to Explore
Bacterial & Fungal Leaf Spot — Xanthomonas & Cercospora spp.
Both powdery mildew and leaf spot pathogens spread in humid, poorly ventilated conditions — the same environmental corrections treat both risks simultaneously.
Read guide
Spider Mite Infestation — Tetranychus urticae
Nutrient-stressed plants susceptible to mildew are also prime targets for spider mites — inspect undersides of leaves for stippling when mildew is confirmed.
Read guide
Stem & Crown Rot — Botrytis & Fusarium spp.
In overcrowded, humid conditions, Botrytis grey mould frequently accompanies powdery mildew — monitor stem bases carefully as humidity increases.
Read guide
