“Cannabis flowers are susceptible to rot or decay post-harvest from a variety of fungi, including Botrytis cinerea, Penicillium species, Fusarium species, Aspergillus species, and Cladosporium westerdijkieae. Post-harvest decay affects yields and the quality of flowers and may cause batches to exceed the acceptable limits for total yeast and mold counts.” 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.
Symptoms
Cameron and Zamir explain that wounds from harvesting and trimming flowers provide openings for these fungi to colonize flower tissues. “Typically, post-harvest infections may begin to be observed within 3-6 days of starting the drying period, with species such as Penicillium, Cladosporium, and Aspergillus causing discoloration and decay of tissues. Small patches of white mycelium may also be observed.”
The researchers explain that fungi may spread during trimming and drying through the air as spores, through contaminated equipment or tools, or in the hands of workers. “During the wet trimming process, wounding of flowers can cause a buildup of spores that can progress to mold development during the drying process. Dry trimming or hand trimming may reduce the buildup of spores. Unsanitary equipment or excessive aerial contamination and inappropriate drying conditions all contribute to post-harvest losses of cannabis.”
Management
Cameron and Zamir give growers some advice on how to prevent post-harvest decay. “First of all, harvested flowers should be examined and be free of visible bud rot. Moreover, in order to minimize the introduction or spread of contaminants, it should be required that shoe covers, gloves, hair and beard nets, and footbaths be utilized. Equipment or tools should be cleaned with detergent and water, as well as a disinfectant. Special attention should be given to trimming machines, including regularly cleaning inside areas where resin and plant debris may build up. Air filtration and purification should also be used in trimming rooms, as the buildup of spores and particulate matter can be high during these operations.”
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.