Downy Mildew 🦠
At a glance
- Cause: Water-mold pathogens that need wet or very humid conditions
- Tell-tale sign: Yellow patches above, gray-purple downy growth below
- Severity: Moderate to serious — can spread fast on susceptible plants
How to identify
Downy mildew usually shows as yellow, pale, or angular patches on upper leaf surfaces with gray, purple, or downy growth on the undersides. It is much more tied to wet foliage and high humidity than Powdery Mildew.
What causes it
Downy mildews require wet or very humid conditions to infect and sporulate. Cool temperatures, crowded plants, and poor airflow make outbreaks worse.
Treatment & management
Following Integrated Pest Management:
- Remove infected leaves or plants quickly if spread is active.
- Keep foliage dry and avoid overhead irrigation.
- Increase spacing and airflow.
- Do not compost infected material if disease pressure is high.
- Fungicides are preventive and may be needed only on valuable, highly susceptible plants.
Prevention
Water at soil level, avoid crowding, and choose resistant varieties where available.
Affects (in this guide)
Many ornamentals, vegetables, and greenhouse plants; uncommon but possible in humid plant rooms