Powdery mildew is the generic term for a group of moulds that can infest cannabis plants and cover them with a white, grey or brownish coating. Unlike many other moulds, downy mildew also thrives well when the humidity is low. Generally, a distinction is made between true and downy mildew:
Powdery mildew (Erysiphaceae):
It is found on the upper sides of the leaves and is first visible as a white, later as a brownish coating. The outbreak is usually triggered by excessive temperature differences between day and night. It thrives best at a humidity of 70% and temperatures around 20°C, much to the dismay of growers.
- Damage pattern:
A white, mouldy coating forms on the leaves, later also on the leaf axils. The leaves turn brown, dry out and eventually fall off. If the leaf axils are affected, even the stem can rot and the plant can fall over.
- Antidote:
Lowering the humidity and raising the temperature to above 25°C has proved effective. In addition, the plants should be sprayed with a mixture of 9 parts water and one part milk. This spraying can also be done very well as a preventive measure. Plants that are sprayed with this milk mixture once a week are much less likely to contract powdery mildew. However, the milk ratio must not be increased under any circumstances, otherwise you will breed other moulds!
Downy mildew (Peronosporaceae):
It forms grey to greyish-purple braids on the undersides of the leaves and white, yellowish and reddish-brown spots on the upper side. These are bordered by the leaf veins. It deprives the plant of nutrients that it needs to grow and thus damages it.
- Damage pattern:
It forms limited spots on the upper side and a fungal network on the underside of the leaf, which can be easily inspected with a microscope or magnifying glass. The leaves turn yellow from the tip and eventually fall off.
- Antidote:
The following can be used Copper-based spraying agent can be used, but these have only a limited effect and should not be used after the flowering phase. There are also highly effective natural fungicides, such as Fungitotal from Agrobeta or chemical fungicides, such as Domark EVO.
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