Many fungal species
Powdery mildew on dogwood (Penn State Department of plant pathology and Environmental Microbiology Archives, Bugwood.org)
Powdery mildew (Whitney Cranshaw, Colorado State University, Bugwood.org)
Hosts, Symptoms & Signs
- many hosts; powdery mildew species are usually host- or group-specific
- white powdery growth on green plant tissue
- commonly occurs on the tops of leaves, but may be on the undersides of leaves, young stems, buds, flowers and young fruit
- overwinters on plant debris as survival fruiting structures (cleistothecia) or mycelia
- in spring, spores from overwintering cleistothecia are spread to new tissue via rain, irrigation, wind or insects
- young, succulent growth is most susceptible
- only moderate humidity is needed to germinate spores
- powdery mildews are common in warm, dry climates
- Manage trees to improve or maintain overall health.
- Powdery mildew in ornamentals is an aesthetic problem; tolerate powdery mildew.
- Use powdery mildew-resistant plants.
- Avoid late summer nitrogen applications.
- Apply fungicides when the first small white spots are discovered. Once the entire leaf is colonized, fungicide applications will be less effective.
- Apply a fungicide (chlorothalonil; potassium bicarbonate; sulfur) to affected foliage. Note: Sulfur can only be applied at temperatures below 90 degrees F; temperatures must stay below 90 degrees F until the fungicide has dried.
- Test ornamental fungicides for phytotoxicity (plant damage) on a few leaves before applying fully.