It develops above all in the presence of humid, moderately warm climatic conditions.
The Oidium, also called "white mal" is a fungus that affects many plants of forest origin or ornamental and fruit. The symptoms are easily recognizable: the plants hit by Oidium are covered on the green organs with a whitish mold of a powdery consistency, constituted by the mycelium of the fungus, while the leaves first decolorate in some areas then curl up and detach from the branch. The flowers have no better fate: the buds find it difficult to open and develop properly, while the branches stop their development and are covered with lateral branches very close together called scopazzi. The plant is damaged not only from an aesthetic point of view, but also the capacity for photosynthesis and therefore the development itself is compromised. The disease spreads more easily in hot and humid climates and with poor aeration, even if heavy rain hinders its spread. The most affected species are roses, begonias, plane trees, oaks and maples. To reduce the effects of the Oidium, limit the excessively luxuriant growth of the plant and therefore reduce nitrogen fertilization, development pruning and irrigation. Remove infected organs if possible. Finally, in nurseries, in spring and autumn, preventive treatments based on wettable sulfur can also be performed. In the case of an oidium infestation we will first proceed by eliminating the diseased parts, if possible, after which with an appropriate fungicide we will carry out treatments taking care to spray the infected part with a sprayer pump paying attention not to leave out any part of the plant. Treatments will be carried out on a fortnightly basis until the conditions favorable to the development of the fungus will disappear.