Oidium

''This article is about a type of fungal spore. For the ascomycete genus, see Oidium (genus). For the fungus that causes powdery mildew on grapes, see 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.

Reference

 * Illinois Mycological Association glossary

Oidium