Powdery mildew is a fungal disease that appears as white, powder-like spots on cannabis leaves and stems.
What Is Powdery Mildew?
Powdery mildew is caused by fungal spores that thrive in environments with poor airflow, high humidity, and inconsistent temperatures. Unlike many molds, it does not require standing water to spread and can develop even in relatively dry conditions.
It commonly starts on upper leaf surfaces but can spread quickly if untreated.
How Growers Get PM
Growers encounter powdery mildew when:
- Airflow is insufficient
- Humidity fluctuates too much
- Plants are overcrowded
- Spores are introduced from outside sources
Early detection is critical to preventing spread.
Why Powdery Mildew Matters
Powdery mildew matters because:
- It reduces photosynthesis
- It weakens plant health
- It can spread rapidly through a grow space
- In late flower, it can ruin harvest quality
Severe infections may require plant removal.
Limitations & Notes
Powdery mildew is not always visible immediately. White spots are a late symptom, and spores can be present before visible signs appear. Prevention is easier than treatment.