Bud Rot (Botrytis cinerea)

Last updated: June 15, 2021

What Does Bud Rot (Botrytis cinerea) Mean?

Bud rot is a disease affecting cannabis plants caused by the fungus Botrytis cinerea. Grey mold produced by the fungus will rot the cannabis flower from the inside out. For this reason bud rot can be near impossible to detect until it is too late.

Cannabis flower infected with bud rot is not safe for consumption and must be disposed of, however, the rest of the plant may be saved if quick action is taken to remove the afflicted portions. Infected plants should be quarantined to protect the rest of the crop.

Cannabis plant infected with bud rot or botrytis


Maximum Yield Explains Bud Rot (Botrytis cinerea)

The term bud rot is generally specific to cannabis plants, however Botrytis cinerea afflicts many other types of plants, including wine grapes, beans, and strawberries. In general horticulture, it is known as grey mold or fruit rot. There are around 30 other species of Botrytis such as Botrytis capsularum and Botrytis fabae.

A necrotrophic fungus, Botrytis cinerea can attack cannabis at all stages of growth, but is most prevalent in the flowering stage and can be devastating to a crop. Cannabis plants afflicted with bud rot can perish within one week.

The spores of the Botrytis cinerea fungus are spread by the wind and enter the plant via tears or wounds in the plant’s tissue caused by pruning or pest damage. It often burrows into the plant’s stem right where the stem meets the soil. Once inside the stem, the fungus starts to rot the stem tissue which can cause young plants to collapse or fall over, referred to as ‘damping off’. Once the plant’s stem has been infected, the fungus then spreads to the flowers. The leaves turn brown, the plant wilts, and the buds become covered in a fine gray or brown fuzz. As the fungus progresses, the buds start to rot and turn slimy.

Prevention is the key to controlling bud rot. The fungus typically thrives when the weather is cool but the humidity is high. The mold of Botrytis cinerea is the most noticeable on the moist areas of the plant. You should keep your plants dry and warm. Ideally, the growroom temperature should be maintained over 70 degrees Fahrenheit and the relative humidity maintained below 50 percent.

If a plant becomes infected with bud rot, it may be saved by carefully removing infected leaves and buds. However, oftentimes the plant is a complete write-off. If the majority of the plant is infected it should be discarded.

Plants may be treated with a copper sulfate or other cannabis-safe, organic fungicides or fungistats. Sulfur burners also reduce the airborne spores of the fungus.



Botrytis cinerea, Fruit Rot, Grey Mold, Gray Mold, Grey Mould, Gray Mould

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