Leveillula taurica (anamorph: Oidiopsis sicula)
The first symptoms include a light green to bright yellow lesion developing on the upper leaf surface. Eventually, a light powdery fungal sporulation forms on the lower leaf surface. Under ideal conditions, white powdery masses of conidia will develop on both surfaces of the leaf. As the disease progresses the lesions become necrotic, and if it is severe the whole leaf dies. Affected plants may be defoliated, resulting in reduced yields, smaller fruit sizes and sunburned fruit.
Conditions for Disease Development
This fungus has a wide host range on which it can survive and spread to tomatoes. Powdery mildew conidia can travel long distances on air currents and are able to germinate under low (52-75%) relative humidity. Disease development is favored by warm (27°C, 80°F) temperatures, however; the fungal conidia can germinate between 10-32°C (50-90°F).
A good fungicide spray program can help reduce losses from this disease.