Bud Rot Prevention and Treatment
Bud rot (Botrytis cinerea) is every grower's nightmare — a grey mould that destroys buds from the inside. Prevention is everything because once it appears, the affected buds cannot be saved.
What Causes Bud Rot
Botrytis cinerea is a fungal pathogen that thrives in high humidity (above 50% in flower), poor airflow, dense buds, and temperatures between 15–25°C. Outdoor growers in autumn, and indoor growers with inadequate ventilation are most at risk. The spores are everywhere — you cannot eliminate them, only create conditions where they cannot establish.
Early Detection
Bud rot starts in the middle of large, dense buds where you cannot see it. By the time you see grey fluff on the outside, it has already spread inside. Check your densest buds by gently separating the calyx layers to inspect inside. Early signs: a single brown, dying leaf sticking out of a bud, white fluffy growth inside the bud, unusual brown or grey patches.
Dealing With Affected Buds
There is no treatment that saves affected tissue — remove it immediately. Cut at least 5cm below the visible rot into healthy tissue. Seal the infected material in a bag immediately and remove from the grow room. Sterilise your scissors with isopropyl alcohol between cuts. Inspect all surrounding buds carefully — Botrytis spreads via airborne spores.
Prevention Strategy
Maintain humidity below 45–50% throughout flowering — this is your primary defence. Ensure strong airflow through and under the canopy. Remove dead or dying leaves immediately. Lollipop heavily to improve airflow in the lower canopy. Silica supplements strengthen cell walls and improve botrytis resistance. Bacillus subtilis (Serenade) sprayed preventatively has shown good results.
Quick Tips
- If outdoor weather forecasts rain during late flower, consider harvesting early rather than risking rot.
- Morning is the highest-risk time for humidity spikes outdoors — check your plants after sunrise.
- Choose mould-resistant strains if you grow in a humid climate — Royal Queen Seeds, Dinafem, and others list mould resistance in strain data.