ID Aids for powdery mildew disease

As summer starts to fade and autumn approaches, there is much variability in the weather. Some days are rainy and humid, others are hot and dry, and the nights are noticeably cooler—ideal conditions to see symptoms of powdery mildew on plants, trees, fruits, or vegetables. But exactly what is powdery mildew?

Powdery mildew is a common name for diseases caused by fungi within the order Erysiphales, all united by that tell-tale symptom of a fuzzy, whitish mat or spots on its host. These obligate parasites differ in their host plants, but they thrive and proliferate in the fluctuating conditions felt around this time of the year. Host symptoms can depend on a several factors, such as the host’s species, age, and part infected, yet an infection rarely causes death. The range of signs include: necrotic spots, color change or leaf curling; dwarfed or distorted fruits and flowers; or there may be no visible symptoms.

This set of ID Aids explores powdery mildew disease, including some of the commodities it affects and the organisms that cause it.

Mango Powdery Mildew

University of Hawaii at Manoa, United States of America

This Oidium mangiferae fact sheet includes discussion of pathogen dissemination and symptoms and has good photos of the symptomatic host.

Grape Diseases in the Southern Interior of British Columbia

Cornell Cooperative Extension, United States of America

This image collection shows symptoms of powdery mildew on different plant parts, among other grape diseases.

Tree Fruit - Powdery Mildew of Apples

British Columbia Wine Council, Canada

Cornell's IPM fact sheet covers Podosphaera leucotricha’s signs and symptoms on apples and includes a helpful diagram showing the disease cycle.

(Obligat) Phytoparasitische Kleinpilze: Echte Mehltaupilze (Erysiphales) ([Obligate] Phytoparasitic Small Fungi: Powdery Mildew)

Kruse, J., Germany

Click on a host name in this German list of powdery mildew fungal species and their hosts to view image galleries of host symptoms. Some are micrographs of the fungus itself.

Biodiversity Reference: Erysiphales (Powdery Mildews), Biodiversity Reference, Scotland

Web page focuses on fungi found in the U.K; includes biology, ecology, symptoms, and excellent photographs of fungal morphology.

Drawings of Erysiphales

Global Information System for the Biodiversity of Plant Pathogenic Fungi, Germany

This search connects users to many plate illustrations from the out-of-print book “A Monograph of the Erysiphales (Powdery Mildews).”

Key to the Genera of Powdery Mildew Fungi

North Carolina State University, United States of America

Key covers eight major genera using fungal cleisothecial appendages and asci characters. Instructions for preparing sample slides and a glossary of terms are also available.