“On cannabis, Botrytis primarily infects the flowers, especially in high humidity environments. This results in soft, rotten, discolored flowers and is commonly referred to as bud rot. If this disease is not managed effectively, it can quickly spread through a growing environment, resulting in severe losses.” Therefore, one section in the Handbook of Cannabis Production in Controlled Environments (in chapter 8, written by Cameron Scott and Zamir Punja, a book edited by Youbin Zheng) helps growers identify and manage this potential threat. “Fusarium species and Sclerotinia may also cause bud rot, although Botrytis cinerea is the predominant cause of this disease.”
Symptoms
Cameron and Zamir explain that on cannabis plants, bud rot may start on the outside of flowers, especially if wounds are present or from the interiors of flowers near the nodes where they are most dense, and humidity is highest. “Flowers infected with Botrytis will initially appear soft and discolored before advancing to being crisp, light brown, and desiccated. Leaves near affected flowers may also appear brown and dry and can be a characteristic symptom to scout for. Gray or off-white mycelial growth may also be observed on affected flowers.”
The researchers emphasize that, even with consistent scouting and removal of infected buds throughout cultivation and harvest, Botrytis-infected flowers may still be present in the post-harvest environment. “These flowers may not have signs and symptoms that are the same as infections pre-harvest. Mycelial growth may spread over buds placed closely together if the relative humidity and air movement in the drying room is not managed appropriately.”
Management
Cameron and Zamir give growers some advice on how to prevent the spread of Botrytis. “First of all, minimize the introduction and spread of the pathogen in contaminated plant debris, or potentially spores on shoes or clothing of staff and visitors. Reduce the use of spores in the growing environment through the use of air purification and filtration systems. Moreover, maintain relative humidity at levels below 50-60% to limit infection and minimize fluctuations in temperature. Of course, it is important to remove infected flowers as soon as they appear. Also, it helps to select strains that are not known to produce overly dense inflorescences, as they tend to trap moisture and maintain high humidity.”
Click here for the Handbook of Cannabis Production in Controlled Environments, in which you can read the full chapter 8: Management of Diseases on Cannabis in Controlled Environmental Production.