Cannabis greenhouse disease diagnosis and integrated management, including powdery mildew, Botrytis, root disease, HLVd, sanitation, irrigation, airflow, and post-harvest microbial risk.
Protected Cultivation
Humidity, Condensation & Dew-Point Risk
Condensation forms when a surface reaches or falls below the air's dew point. In protected structures, cold glazing, leaves, pipes, and dense flower zones can become wet even when bulk-air RH appears acceptable.
Key concepts
- Relative humidity changes with temperature even when absolute moisture is unchanged
- Cold surfaces can reach dew point before room air appears saturated
- Night cooling often raises condensation risk
- Persistent leaf or flower wetness can increase disease risk
What to measure or observe
- Track temperature and RH overnight
- Inspect glazing and crop surfaces near dawn
- Compare air temperature with leaf or surface temperature when possible
- Note locations where condensation repeatedly forms
Common mistakes
- Using daytime RH as the only disease-risk metric
- Assuming visible wall condensation is the only meaningful condensation
- Heating without considering moisture removal
- Dehumidifying one zone while leaving stagnant canopy pockets
Visuals this lesson still needs
- Dew-point concept diagram
- Night condensation sequence
- Cold-surface risk map
- Leaf versus air temperature graphic
Evidence & further reading