Professional area | Diseases factsheet | Fungi | Oïdium cyclaminis : Powdery mildew
Oïdium cyclaminis attacks Cyclamen flowers.
The spores of this fungus, spread on the wind, cause a white powdery mildew on the petals.
The attacks, which take place in warm, humid weather, are fairly rare; but they can cause serious damage to flowering.
The disease can be controlled by chemical means.
Oïdium is a fungus in the class Ascomycetes, i.e. septate fungi which produce ascospores in sexual reproduction. Oïdium belongs to the Erysiphaceae family.
Oïdium cyclaminis attacks the flowers of cyclamen, which is virtually their only host, apart from a few other flowering plants: apparently it attacks nothing but the flowers.
Oïdium attacks are almost exclusively confined to the outward surface of the plant; the mycelium does not directly penetrate the plant’s tissues.
A spore, wafted most probably on the wind, gets into the glasshouse and lands on a flower. In many levels of temperature and humidity (even low ones, though they are less suitable) it germinates, to produce a whitish powdery mycelium. Optimum temperature for mycelium development is around 25ºC (77ºF), while low temperatures put a stop to development and high ones kill it.
Oïdium does not need water in liquid form for its development: indeed, in water the spores quickly lose the power to germinate, while warm, moist air is most conducive to germination. There is considerable risk from April to November.
The mycelium makes swift progress. The little patches are a few millimetres across at first, but they grow. They then begin to look like a white powdery fuzz, easily wiped off with the finger. This appearance is due to the chain production of spores: within 5 to 7 days, an infected plant is showing other spores in its turn. Spore formation and germination are at their maximum at around 21ºC (70ºF) to 25ºC (77ºF).
One of the fungal mycelia carries a number of ‘suckers’ called haustoria. These can pass through the epidermis and penetrate the petal cells, to feed at the host’s expense: the cells affected die, and in the end the petal withers.
The conidia, or asexual reproductive spores, are small, light and easily carried on the wind. They can enter glasshouses through ventilation openings or simply through doorways. They remain viable for 30 days, but cannot stand drying out. Infected plants are themselves a considerable source of contamination within the glasshouse.
Because the spores are able to germinate even in fairly unfavourable conditions (absence of water), precautions are more or less in vain. All the same, the aim is to restrict changes of temperature and humidity variation, for this is a factor which helps this fungus to develop.
The constant development of the regulations and homologations of phytosanitary treatment products, and the differences in regulations according to each country make it impossible for us to include updated information on homologations. Each producer will have to contact his local plant protection bureau to obtain the latest updates concerning the regulations and use of phytosanitary products. We strongly advise testing beforehand on a plant sample in order to measure the chemical’s activity (establishing the dose) and any effect on the plant (plant poisoning).
This advice sheet is based on the methods used at the SCEA at Montourey (Fréjus, France). These procedures may need some modification to adapt them to other climatic situations. Before starting to grow cyclamen there needs to be a review of precautions against pests and diseases. We must point out that our advice and suggestions are offered for information purposes and therefore cannot include any guarantee of specific results; it is a good idea to carry out trials beforehand.
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