The presence of pathogens and molds during the cultivation, harvest, and curing of crops has plagued cultivators of all plants for as long as people have been farming them. Pathogens can cause diseases that reduce plant growth, and molds can impact the quality of crops, even after harvest. The process of cultivating cannabis is no exception. Producers are already aware of this as are most consumers, but a recent study  takes a deep dive into the pathogens and molds affecting cannabis specifically. It contains some very interesting findings.
The study was conducted in Canada over the course of three years between 2016 and 2018. Samples were taken from various cannabis cultivars and included plant tissue from different parts of the plant, growing mediums, and the surrounding air. Samples were collected at various times throughout different periods of the plants’ life cycles as well as different periods of the cultivation and production processes. Locations where samples were obtained included hydroponic indoor cultivation facilities, in grow rooms with controlled environments and greenhouses, as well as outdoor cultivation fields.
Pathogens and molds were isolated and observed in their respective methods, including plant dissection, scanning electron microscopy, endophytic colonization, and others. However, the cultures were all positively identified using “a [polymerase chain reaction]-based assay using primers for the internal transcribed spacer region (ITS) of ribosomal DNA…” 
By testing so many variables using various methods over an extended timeframe, a lot was discovered. Pathogens infecting roots caused discoloration, stunting, and plant death. They “included Fusarium oxysporum, Fusarium solani, Fusarium brachygibbosum, Pythium dissotocum, Pythium myriotylum, and Pythium aphanidermatum.” 
The major pathogen affecting foliage was attributed to Golovinomyces cichoracearum, causing powdery mildew. Several types of bud rot were found to be caused by the presence of either Penicillium olsonii, Penicillium copticola, Botrytis cinerea, F. solani, or F. oxysporum.
Indoor growing facilities were found to have various amounts of Penicillium, Cladosporium, Aspergillus, Fusarium, Beauveria, and Trichoderma in the air (the latter two from biocontrol products), as well as Cladosporium, five species of Penicillium, and different species of Alternaria in their coconut fiber growing mediums.
Another important note was determining that “mechanical trimming of buds caused an increase in the frequency of Penicillium species, presumably by providing entry points through wounds or spreading endophytes from pith tissues.”
Distribution of these pathogens and molds were most common through the air, growing mediums, and entry through wounded plant tissues. Cannabis cultivators should keep these three major points in mind when addressing concerns of pathogens and molds affecting their crops.
- Punja Z, et al. Pathogens and molds affecting production and quality of Cannabis sativa Frontiers in Plant Science. 2019;10(1120). Times Cited: 13 (Semantic Scholar); Journal Impact Factor: 4.402