The epidemiology of Oidium neolycopersici obligate parasite is not well known.

• Conservation, sources d'inoculum
  

Like many powdery mildews, it must be able to persist from year to year in several ways:
- through plants alternative , cultivated or weeds. Its range of potential hosts is quite wide; it seems to differ from one country to another, which makes it possible to suppose that this species would contain more or less specialized forms. Artificial inoculations made it possible to assess its aggressiveness on various plants. It hardly settles on melon, cucumber, zucchini, peas and Solanum dulcamara ; it grows more on eggplant, potato, Solanum albicans , S. acaule and S. mochiquense persist , but does not there. On the other hand, tobacco is very sensitive to it and could constitute an alternative host. Datura stramonium , Solanum capsicoides , S. jamaicense, S. laciniatum, S. lycopersicoides, S. ptycanthum, Petunia hybrida also seem rather receptive. Moreover, given the length of the tomato production cycle under shelter, O. neolycopersici must be able to be maintained on this plant, in its mycelial form, from one year to the next;
- thanks to globular cleistothecia (perithecia without ostiole) that could ensure its sexual reproduction.

As we have already clarified, the teleomorph of this fungus has never been observed , so it should not play an important role in its biological cycle.

• Penetration and invasion

The conidia of O. neolycopersici most certainly provide the primary contaminations . Once in contact with the host, they germinate quickly in a few hours if the surrounding conditions are favorable. They form an appressorium , then enter directly into the epidermal cells, developing haustoria . The latter play the role of suckers allowing the removal of the elements necessary for the growth of the mycelium of the fungus.
 

• Sporulation and dissemination

Within a few days of infection, short conidiophores emerge on secondary hyphae formed on the surface of the leaf blade and produce conidia (Figure 1). Sporulation is very abundant. Conidia are quite fragile and only live for a few hours, or even a few days, when conditions are favorable. They are very light and are therefore easily transported and dispersed by the wind , and incidentally by rain or splashing during sprinkler irrigation.

• Conditions favorable to its development

O. neolycopersici relative prefers humidity of or less 80% ; above, its development is gradually reduced. Therefore, excessive humidity would lead to a reduction in the severity of the disease. A high nitrogen content of leaf tissues will weaken them to this powdery mildew. This mushroom particularly appreciates humid and hot environments .