''Podosphaera clandestina'' var. ''clandestina'' is a

plant pathogen Plant pathology (also phytopathology) is the scientific study of diseases in plants caused by pathogens (infectious organisms) and environmental conditions (physiological factors). Organisms that cause infectious disease include fungi, oomyc ...

that causes a

powdery mildew Powdery mildew is a fungal disease that affects a wide range of plants. Powdery mildew diseases are caused by many different species of ascomycete fungi in the order Erysiphales. Powdery mildew is one of the easier plant diseases to identify, as ...

in apricots and peaches.

References

Fungal tree pathogens and diseases Stone fruit tree diseases clandestina var. clandestina {{fungus-tree-disease-stub