White powdery mildew, a fungus, manifests itself initially on the leaves, petioles and the flower heads, with the appearance of a characteristic whitish efflorescent, floury, constituted by the abundant formation of mycelium and conidial multiplications of the fungus.
Following such infection the leaves become smaller, curled up and of leathery consistency. In a short period the white efflorescence turns into a purplish brown colour. Following this the affected organs dry up and die.
The flowers often do open and necrotic spots appear on the stems. Even if the pathogen does not cause the death of the plant and chemical control is not carried out in time, the total deterioration of the flowers will be the result. The mildew flourishes in warm-damp conditions, but the ability to germinate and to spread, even when the relative humidity is low, and a broad range of temperature – min 3-4 C, opt 20-25 C and max 35-36 C – makes this pathogen dangerous in any period of the year. The fungi resting structures during winter are the cleistothecia that in spring first release the ascospores and from these the conidia. These are transported by wind and reach the leaf surface of the Gerbera on which they will germinate and produce the disease. Not all Gerbera varieties are affected in the same way. This depends on the susceptibility of individual varieties. White powdery mildew generally appears in small amounts and then usually spreads quickly and widely on the same vulnerable variety. It is always essential to act quickly at the first signs of the infection.
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