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Powdery Mildew Disease

Photos courtesy of Larry Costello PhD - University of California


There are many diseases that fall under the general description of powdery mildew, but they are all a species of fungi. Host plants are of all types - vegetables, fruit trees, grapes, roses, ornamental trees and shrubs. The fungus is composed of mycellium and spores (conidia) which are wind-blown to other plants or other parts of the same plant. Powdery mildew is host specific, meaning that the mildew on a rose, for instance, will not spread to another species. It is also a type of fungi that can only grow on living plant tissue.


The white powdery growth consists of the fungal mycellium and reproductive spores. It can cause mild to severe damage to plants. Young plants and those with actively growing shoots are more severely damaged than older plants. Infected leaves may be dwarfed, curled, or deformed.  And some plants may drop their leaves without development of the obvious white powdery substance.

Conditions under which powdery mildew thrive are moderate to high humidity, lack of air circulation, and low light. And, unlike many pathogens, this mildew fungi infect their hosts in the absence of free water.

Download a PDF about Powdery Mildew Disease as part of a Tree Wellness Program

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