OIDIUM...Uncinula necator

An oidium (plural: oidia) is an asexually produced fungal spore that (in contrast to conidia) is presumed not to constitute the main reproductive preoccupation of the fungus at that time. The hypha breaks up into component cells/ small pieces and develop into spores. Oidia can't survive in unfavourable conditions. Uncinula necator is a fungus that causes powdery mildew on grape. It is a common parasite of grape (Vitis vinifera). The fungus originated in North America. European wine varieties of Vitis vinifera are more or less susceptible to this fungus. Uncinula necator infects leaves and young berries, and can cause large damage if untreated. This parasite does not need drops of water to infect the plant leaves; high atmospheric humidity is enough. Its anamorph is called Oidium tuckeri.
This mildew can be treated with sulfur or fungicides, especially Strobilurines. Uncinula can develop resistance to organic fungicides, so it is important to use different (rotate) fungicides during one season (for example, using two or three different types of organic fungicide and sulfur). The parasite can not develop resistance to sulfur, but efficacy of this fungicide is not as high as the organic ones. But sulfur can be used as a prevention for this plant disease.