Latin names: Erysiphe, Leveillula, Sphaerotheca … varies with species

Common name: Powedery Mildew

Plant family affected: varied, but consistent on cucumber, melons, squash, and pumpkins and some flowers like bee balm.

Date/Location of specimen: Oct. 2, 2015 on coreopsis at client’s landscaping near Waynesburg.

Description: Powdery mildew is a common disease on many types of plants. There are many different species of powdery mildew fungi (e.g., Erysiphe spp., Sphaerotheca spp.) and each species only attacks specific plants … Powdery mildew first appears as white, powdery spots that may form on both surfaces of leaves, on shoots, and sometimes on flowers and fruit. These spots gradually spread over a large area of the leaves and stems… Leaves infected with powdery mildew may gradually turn completely yellow, die, and fall off … Most powdery mildew fungi grow as thin layers of mycelium (fungal tissue) on the surface of the affected plant part. Spores, which are the primary means of dispersal, make up the bulk of the white, powdery growth visible on the plant’s surface and are produced in chains that can be seen with a hand lens; in contrast, spores of downy mildew grow on branched stalks that look like tiny trees.
Powdery mildew spores are carried by wind to new hosts. Although humidity requirements for germination vary, all powdery mildew species can germinate and infect in the absence of free water.1


Collection Sample # 2 of 5 DISEASES

Master Gardener Class Horticulture Portfolio