Plant Health ProblemsThe disease problems on sage are similar to those of other herbaceous annuals. See Herbs for a detailed discussion of these diseases.
Diseases caused by Fungi:
Powdery mildew, Erysiphe
White powdery spots or patches develop on leaves and stems. Symptoms often first appear on the upper surfaces of the leaves. Heavily infected leaves turn brown and shrivel.
Disease can be minimized by avoiding overcrowded spacing of plants and by carefully picking off affected leaves as soon as symptoms are evident. Symptomatic leaves can be placed into a plastic bag in order to avoid spreading the spores of the fungus to other plants. Use of fungicides is usually not necessary. However, for ornamental, not culinary plants, applications can be made as soon as symptoms are visible. Among the compounds registered for use in Connecticut are thiophanate-methyl, potassium bicarbonate, and sulfur. Consult the label for dosage rates and safety precautions.