Leveillula taurica is an obligate fungal pathogen, from the phylum Ascomycota, which causes powdery mildew on onion.

L. taurica is the pathogen responsible for powdery mildew on onions, but it can also infect peppers, tomatoes, eggplant, cotton, and garlic.

An accurate way to describe its host specificity is that this disease is, “a composite species consisting of many host-specific races.

"[3] Symptoms of Onion Powdery Mildew (OPM) are usually seen as circular or oblong lesions that are 5 to 20 mm and have a chlorotic or necrotic appearance.

The conidia exit through the host’s stomata and serve as a secondary inoculum to spread disease after initial infection.

Species within the genus are adapted to xerophytic conditions, exemplified by the ability of their conidia to germinate rapidly and at any relative humidity.

[6] L. taurica is primarily a disease of allium species—it has been documented on onions and garlic in Israel and southeastern Europe—but can also infect other species, including cucumbers, peppers, eggplants and tomatoes.

The economic importance of OPM is limited, as the disease is sporadic, and it rarely progresses enough to make fungicide treatment necessary.

[9] The disease geography within the United States is limited to Idaho, Utah, California, and the Pacific Northwest.