See:
Greenhouse Plants, Ornamental - Powdery Mildew
Cause Golovinomyces cynoglossi (formerly Erysiphe cynoglossi) is a common garden problem. This fungus is favored by conditions that produce high humidity but dry leaves. It is a highly specialized pathogen that forms a close association with the host. Conditions that favor the host also favor the pathogen. Much of the fungus remains outside infected plant parts where it grows on the surface but sinks root-like structures called haustoria into plant cells to obtain nutrients. The white growth seen is composed of both mycelium and fungal spores. Found more frequently after plants flowered and during senescence. Unknown if it is limiting plant growth or production.
Symptoms White patches of dense mycelium, tending to become grayish brown, on leaf surfaces and stems. Leaves frequently show chlorotic mottling. Leaves may eventually turn yellow and wither.
Cultural control
- Space plants for good air circulation.
- Remove and destroy individual leaves if not a bad problem. Remove entire plants when heavily infected.
Chemical control None registered specifically for this crop.
Reference Glawe, D.A. 2004. First report of powdery mildew of Myosotis sylvatica (wood forget-me-not) caused by Golovinomyces cynoglossi (Erysiphe cynoglossi) in Washington state. Online. Plant Health Progress doi:10.1094/PHP-2004-1124-01-HN.