White rusts are not true rust but are more closely related to Pythiums, Phytophthora, and other damping-off fungi. They get their name from the white rust-like pustules which develop on infected plant tissue. Most commonly they are found on crucifers, morning-glory, sweet potatoes, beets, pigweed (Amaranthus), spinach, and moss-rose.
Symptoms generally begin with chlorotic spots on upper surface of leaves. As the infection progresses white, powdery pustules form below the spots on the underside of the leaf.
Control of White Rust Diseases:
1. Follow good sanitation practices. Contol is generally not required but removal of infected leaves or plants can help to limit the spread of the disease.
2. Select resistant varieties. In areas where white rust is a recurring problem seek out resistant varieties.