Podosphaera Clandestina Var. Clandestina

The most reliable sign of this fungus is a thin coating on the leaves of its host, usually on young shoots and new branches. The coating is the fungus's visible growth, and it is what gardeners and foresters notice first.

Podosphaera clandestina is fairly host-specific and infects only a few genera. That narrow host range helps separate it from other mildews on the same plants.

On hawthorn, Crataegus, another powdery mildew also occurs: Phyllactinia mali. Its growth is weak, very thin and often smooth, and it forms on the undersides of leaves.

Podosphaera clandestina is found across the world. It affects plants in the genera Crataegus, Cydonia and Mespilus, so its range follows the spread of these hosts.

Its known habitat is the host plants themselves, mainly young shoots and new branches. The fungus grows on the leaves of these trees and shrubs.

Observation records peak from July to September. Records are highest in August, with 1,681 observations, followed by July with 1,126 observations and September with 688 observations. Fewer than 30 observations are recorded from November to February, and the counts show when the fungus is most often seen rather than how abundant it is.