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White powdery mildew, more commonly known as PM, is a fungal disease which grows and spreads rapidly.

On a living host it reproduces both sexually and asexually. It spreads by releasing spores which settle elsewhere, where they continue to grow and reproduce. Powdery mildew can slow down the growth of your cannabis plant, and in severe instances it can kill your plant entirely.


Identifying PM during the early stages is not difficult to do – for the vigilant grower.

The white, fluffy, spongey, fuzzy fungus stands out again the green of the cannabis plant’s leaves. Once identified, the powdery mildew needs to be dealt with thoroughly and with great care; so as to prevent the spreading of the spores.


Powdery mildew is best prevented by controlling the environmental factors which cause it to develop:

  • PM thrives in areas of high humidity and moisture. Growers living in areas of high humidity can make use of dehumidifiers to keep the moisture levels of the grow area at an optimal 40 – 60 % RH.
  • Poor airflow and circulation will encourage the spores to settle and grow. Make sure you are using decent fans to keep the air moving in your grow area. Spores can often settle in fans and ventilation systems; be sure to clean those regularly too. Many growers clean and disinfect their grow areas entirely between harvests. A clean grow is a happy grow.
  • Good ventilation allows fresh air to enter and old air to leave. Without proper ventilation, PM spores will spread easily around the grow area as they remain in circulation.
  • When plants are spaced too closely together, their leaves touch one another creating a moist spot for powdery mildew to develop. Pruning and trimming bushy plants greatly assists in keeping PM at bay.


Once powdery mildew is identified in your grow area, it must be dealt with immediately and with great care. The spores from PM travel easily when disturbed, making cross contamination the most challenging part of dealing with powdery mildew.

The following are organic measures, which should collectively assist in getting rid of your fungus gnat infestation.

  • If possible, physically remove the leaves with the worst PM infestation.
  • Using a damp paper towel, wipe the PM off of the remaining leaves. Do not use the same paper towel to wipe two different areas. Be careful also not to shake the leaves; causing the spores to fall and travel.
  • Using a foliar spray of your choice, coat your cannabis plant thoroughly. Our favourite foliar spray for PM is a mixture of water and 35% food grade hydrogen peroxide. It is organic, safe enough to use daily, and it kills PM on contact! Other popular options for folia sprays are solutions containing water mixed with either milk, alcohol, bicarbonate of soda or neem oil.
  • Revisit the ‘prevention’ section and ensure that you are creating an environment which is non-conducive to a powdery mildew infestation. Air flow and ventilation are key to keeping PM at bay.



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