Cause The fungus Podosphaera euphorbiae can be found in gardens in western Oregon and Washington. It does not seem to be a debilitating problem as plants continue to grow well despite its presence. Shady locations encourage disease development.
Symptoms White powdery growth can be seen on both sides of leaves. Leaves may be chlorotic and have brown flecking associated with the colonies. Colonies may start out on a few scattered leaves but by end of summer can completely cover the surface of many leaves. Heavily infected leaves may be smaller in size. Stems can also be colonized.
Cultural control
- Space plants far enough apart to ensure good air circulation.
- Pick off and burn affected leaves, if practical.
- Plant in sunny locations avoiding areas with heavy shade.
Chemical control There are no fungicides specifically registered for this crop; however, many labels will allow ornamental use. Test first on a small section before applying on the whole plant to evaluate possible phytotoxicity.
Reference Dugan, F.M., and Newcombe, G. 2007. New records for powdery mildews and Taphrina species in Idaho and Washington. Pacific Northwest Fungi. 2:1-5.