The life cycle of powdery mildews generally starts with a conidia or ascospore landing on the host plant and germinating, although it should be noted that ascospores have not been found in all powdery mildew species. One or two germ tubes are formed and act as a penetration tool. The fungus directly penetrates the host cell wall through enzymatic activity and turgor pressure. After the breakdown, the fungus develops a haustorium to supply it with nutrition.

Powdery mildews reproduce both asexually and sexually. Asexual reproduction starts within a few days of infection. Conidiophores emerge from vegetative hyphae and conidia are produced serially. Conidia are then dispersed through wind over relatively short distances.

When the asexual growing season ends, sexual reproduction occurs via chasmothecia, which are small, round fruiting bodies containing asci, specialized sacs where ascospores are produced. As the nucleus from the male gametangia moves to the female gametangia through plasmogamy, it results in a dikaryotic cell, from which asci develop. The number of ascospores per ascus varies among the species from two to eight. Under favorable conditions, chasmothecia open and release ascospores.

Powdery mildew fungi overwinter in several forms – chasmothecia, bud perennation, and mycelium become active again when favorable conditions return in the spring.