Cannabis Bud Rot Prevention Guide
Learn how to prevent cannabis bud rot and keep your THC products fresh and potent.
Bud rot, also called gray mold, is Botrytis cinerea. It spreads when spores land on wet flower tissue in still air. To stop it, remove every infected bud with sterilized tools, hold relative humidity at 45 to 50 percent, move air through the canopy, and keep night temperatures close to daytime temperatures so condensation does not form. Do this the same day you find the first brown, mushy patch. Spores travel, and a spot the size of a coin can reach a whole room in a few days.
What you need
- Pruning shears or scissors
- 70 percent isopropyl alcohol and a clean cloth
- Disposable gloves
- Sealable plastic bags
- Hygrometer
- Oscillating fan and exhaust fan
- Dehumidifier
Steps to contain the infection
- Move potted plants away from healthy plants, or mark the infected plant so you work on it last.
- Put on gloves and wipe your shears with 70 percent isopropyl alcohol.
- Cut the stem at least 2 inches below the visible rot, into firm green tissue.
- Place each cut bud into a sealable bag and close the bag right away.
- Sterilize the shears again after every single cut.
- Inspect the remaining buds, including the interior of dense colas, for brown or gray fuzz.
- Remove the sealed bags from the grow area and place them in outdoor trash. Do not compost them.
- Set the dehumidifier to 45 to 50 percent and hold that range day and night.
- Run an oscillating fan above the canopy and keep the exhaust fan on at all times.
- Raise night temperature so it stays within a few degrees of the daytime temperature.
- Check every plant twice daily for 7 to 10 days.
- Repeat the removal process at the first sign of any new patch.
Signs to check for
- Brown, gray, or tan patches on flower tissue
- Mushy buds that collapse when touched
- Gray fuzz or dust on the surface of a cola
- Single sugar leaves that turn brown and dry while the rest of the bud looks fine
- A musty or ammonia smell near the canopy
Prevention for the rest of the grow
- Keep relative humidity under 50 percent once flowering starts.
- Defoliate lower growth so air reaches the middle of the plant.
- Water the soil or medium, never the buds or leaves.
- Space plants so leaves from neighboring plants do not touch.
- Reduce nitrogen late in flower to avoid soft, dense growth.
- Clean the room, tools, and hands between runs.
- Stay out of the garden when foliage is wet.
When to harvest early
If rot returns after two rounds of removal, cut the crop early. Cannabis harvested at cloudy trichomes beats a crop lost to mold. Dry the harvest at 60 to 65 degrees Fahrenheit with good airflow and check the drying buds daily for new patches.
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Do not consume moldy flower
Discard every bud that shows rot. Botrytis can trigger allergic reactions and respiratory irritation, and the spores stay on tissue after the visible mold is gone. Cut your losses on the infected material and protect the rest of the harvest.