Cannabis is generally a robust plant, but it can fall victim to fungal infections after blooming in the summer, something that anyone wishing to harvest it should be watching out for.
A 2023 study found that the harmful fungi that contaminate some plants can make people sick, especially if they are immunocompromized and regardless of whether they consume the cannabis for medical or recreational purposes.
Grey mould, a kind of fungus that often appears at the end of flowering and shortly before the harvesting, is what any cannabis plant owner should be looking out for, says Simon Kraushaar from the German Hemp Association (DHV).
The furry grey fungus, also known as "bud rot", mainly appears in cold and wet autumn weather and can be very hard to avoid in outdoor cultivation in some years. However, if you think ahead you can significantly reduce the risk to your plants.
Ensuring good ventilation through wind or draughts is a very effective preventative measure. "Don't plant hemp in a corner that is sheltered from the wind," Kraushaar advises.
It's also important to remove all dead or wilted leaf material regularly. Providing protection from the rain by covering the terrace or balcony can also help.
If you still find grey mould on the flowers, these must be completely cut out and disposed of to prevent the fungal infection from spreading.
Research shows that some fungi in cannabis can cause infections in lung and skin tissues when smoked. This effect appears to be less common in edibles. Cancer, transplant and HIV patients and people with diabetes are thought to be particularly susceptible.