How to Increase Air Circulation to Prevent Bud Rot

How to Increase Air Circulation to Prevent Bud Rot

Bud rot is Botrytis cinerea. The fungus needs free water on plant tissue and relative humidity above 60 percent. Moving air removes that water. Run exhaust fans 24 hours per day. Aim for 1 to 3 air exchanges per minute in the grow room. Keep relative humidity at 40 to 50 percent during flower. Add oscillating fans above and below the canopy. Prune 20 to 30 percent of fan leaves at day 21 and day 42 of flower.

how to prevent bud rot on cannabis plants

Exhaust and intake

Size the exhaust fan in CFM. Multiply room volume in cubic feet by 1 to 3. A 4x4x8 foot tent holds 128 cubic feet. Use a 200 to 400 CFM fan. Place intake vents low and exhaust vents high. This pulls cool air across the canopy. Use a carbon filter to block odors. Keep passive intake area 2 to 3 times the exhaust duct area. Run the fan at full speed during lights on. Reduce to 50 percent at night.

how to increase air circulation to prevent bud rot

Oscillating fans

Mount one 6 to 12 inch oscillating fan per 2 to 4 plants. Aim the fan at the wall, not the buds. Leaves should move 1 to 2 inches. Direct wind on buds causes wind burn. Wind burn creates dead tissue. Dead tissue invites Botrytis. Run fans 24/7. Add a second fan below the canopy to move air through the lower stems. Clean fan blades every 30 days. Dust blocks airflow.

cannabis bud rot prevention using dehumidifier

Humidity and temperature

Keep temperature at 68 to 77 degrees Fahrenheit. Botrytis grows fastest at 59 to 77 degrees. Use a dehumidifier in late flower. A 30 pint dehumidifier handles a 4x4 tent. Target a vapor pressure deficit (VPD) of 1.2 to 1.6 kPa in weeks 6 to 9. Measure RH with a calibrated hygrometer. Place the sensor at canopy height. Avoid overhead watering. Water at the base of the plant. Spores need 4 to 12 hours of leaf wetness to infect. Airflow cuts that time.

Defoliation and spacing

Remove the bottom third of branches at day 14 of flower. This is lollipopping. Space canopy tops 12 to 18 inches apart. Use a trellis net to spread colas. Do not crowd plants. A 4x4 tent holds 4 to 6 plants in 5 gallon pots. More plants means less air per bud. Remove dead leaves from the floor. Dead leaves hold moisture. Clean the tent walls with a 10 percent bleach solution between runs.

Signs of bud rot and removal

Look for brown or gray mushy spots on buds. Gray fuzz appears in 1 to 2 days. Sugar leaves turn brown and curl. Cut infected buds with sterile scissors. Place a plastic bag over the bud before cutting. Cut 2 inches below the rot. Do not compost the material. Seal the bag and discard it. Sterilize scissors with 70 percent isopropyl alcohol after each cut. Check remaining plants every 12 hours for 7 days.