Cannabis greenhouse disease diagnosis and integrated management, including powdery mildew, Botrytis, root disease, HLVd, sanitation, irrigation, airflow, and post-harvest microbial risk.
Diseases
Powdery Mildew
A group of obligate fungal pathogens that produce superficial white growth on susceptible tissues. Early colonies can be small and easy to confuse with residues, so confirmation matters.
What to look for
- White powdery colonies that expand across leaves or other susceptible tissues
- Colonies that may begin as isolated circular or irregular patches
- Repeated appearance on new tissues after incomplete control
Important look-alikes
- Dried spray residue
- Mineral deposits
- Dust
- Trichome-rich tissue at a glance
How to confirm
- Inspect with magnification for fungal structures
- Compare suspected colonies before and after gentle wiping
- Check multiple canopy zones and nearby plants
Management principles
- Remove heavily affected tissue where appropriate without spreading spores
- Improve environmental and canopy conditions that favor repeated disease pressure
- Use a rotation of compatible management tools rather than relying on one repeated input
Prevention
- Quarantine incoming plants
- Maintain sanitation and spacing
- Scout dense canopy zones
- Avoid carrying contaminated material into clean rooms
Visual study guide
- Early colony close-up
- Powdery mildew versus residue comparison
- Spore-production microscope diagram
- Canopy scouting map
Evidence & further reading