Grey mould (lat. Botrytis cinerea) is a fungus genus that belongs to the moulds. It forms cotton-wool to fluffy coatings on the plant surface. The colour changes from initially white to grey, hence the name. It can also be the cause of the fall sickness. Apart from the fact that mouldy grass does not taste very good, it is also harmful to health and can severely stress and even damage the respiratory tract. Grey mould often starts in the middle of buds, especially large and dense buds, and can very quickly destroy the entire crop. Often, the buds look normal from the outside, while the mould spreads inside the flower.

Favouring factors in the occurrence of mould

  • high humidity
  • plants too close together
  • Too little light
  • Poor aeration and ventilation of the plants, no fresh air
  • too big buds

What to do in case of infestation?


There are fungicides such as e.g. Atempo Copper Fungus Free There are fungicides available on the market that only require a waiting period of 3-7 days (from the application of the product to the harvest), but the use of chemical products is not recommended from a health point of view. Affected plants should be removed from the growroom so that they do not infect other plants. Then clean the entire growroom and optimise the ventilation so that the air exchange is better.

Therefore, one should take preventive action above all:

  • Use of so-called antagonists. In our case, these are other fungi or yeasts that compete with the grey mould because they spread faster and thus deprive the grey mould of space and nutrients. Examples are Trichoderma spp. and Pythium oligandrum. The following has proven to be extremely effective Fungitotal from Agrobeta proved to be extremely effective.
  • Use of general strengthening agents for the plants, either through soil bacteria such as Bacillus subtilis, which are intended to stimulate growth and resistance by improving root growth, or through the application of fatty acids and trace elements, which, in addition to increasing the plant's own defences, also strengthen the plant's cell walls so that fungal spores can no longer penetrate the plant so easily, e.g. GHE Organic Essentials, Mineral Magic, Rhizotonic, Vita Race, CANNAZYM or Neudorf Horsetail Extract.
  • Ventilation should be sufficient and fans must also be used in the growroom so that the air is set in motion.
  • The humidity in the growroom should not be too high. The planting medium should be moist, but not wet.
  • Do not spray buds with water, as this may not be able to dry off and mould will quickly form!

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