Cannabis (popularly known as marijuana or weed) is now legal in Canada for both medical and recreational use. In the United States, it has been approved for medicinal use in 33 states and in 11 states for recreational use for adults aged 21 and over.
Moldy Cannabis is a serious problem facing both producers and consumers. In 2019 there were many reports of legal Cannabis being recalled both in Canada and the United States due to mold contamination. Mold growth on Cannabis can prevented.
The prevention of mold growth on Cannabis has to be done at the cultivation/production, processing, distribution and consumer level. While contamination can occur at any of these levels, it can mean total loss of the product if it occurs at the production, processing and distribution levels.
As a Cannabis grower recognising the signs of a potential mold infestation, and how to prevent it is very important. The most common molds that attack Cannabis plants during cultivation are Botrytis (bud rot) and powdery mildew. While powdery mildew is not a post-harvest problem Botrytis can be a problem in the field and also on harvested dry leaves.
The powdery mildew was thought to be caused by the fungi Podosphaera macularis or Golovinomyces (Erysiphe) cichoracearum but molecular studies suggest the Cannabis powdery mildew could be caused by a different species.
As the saying goes, prevention is better than cure. By focusing on sound agronomical practices, Cannabis growers can significantly minimize the risk of mold growth on their crops. The potential for Cannabis infection by airborne mold and pathogen spores can be monitored by collecting air samples for analysis.
For Cannabis grown indoors, Botrytis and powdery mildew thrive well under cool temperatures, stagnant air, and wet or humid conditions. Therefore, the best way to prevent both diseases is to ensure proper air circulation and maintaining low humidity.
It’s important that processing is performed in a clean, dry environment. Marijuana for smoking should not be transported or stored in a damp, humid environment. The end consumer should also ensure that they store their weed in a clean and dry environment.
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