Plants Die Out From Dieback Disease
While Ajuga is typically dependable and vigorous, every once in a while patches of it will suddenly die out. Clean up the remaining dried, shriveled foliage and leave the roots alone. Chances are next season the plants will regenerate from the roots. Try to avoid using chemical herbicides near ajuga, they seem to promote rot in existing plants.
Crown and Roots Rot; Odor Present is Caused by Crown Rot
Soil-dwelling fungi cause this serious disease, which can kill plants within a few days. Spots appear on the crown (where stem and roots meet), lower leaves rot and young shoots wilt. Roots blacken and become covered with white fungal threads. Overcrowded plantings and excessive fertilizer encourage the growth and spread of this disease.
There is no known cure, so remove and discard infected plants and the soil immediately surrounding their roots. It is advisable to replace infected ajugas with a different groundcover. Thoroughly cultivating around plants encourages the soil to dry out and hinders the spread of the fungus. Clean up plant debris in the fall and discard it in the trash to prevent overwintering of disease spores. For more information see the file on Controlling Fungal Disease
Leaves Covered With White Powder Due to Powdery Mildew
Powdery mildews are caused by fungi that cover ajuga leaves with a white or ash-gray powdery mold. Badly infected leaves become discolored and distorted, then drop off. Powdery mildews thrive in both very humid or very dry weather. They are not usually life threatening to established plants, but mildews do mar their appearance. To prevent the spread to nearby areas covered with ajuga, spray the uninfected plants with a garden sulfur fungicide according to label instructions. Clean up debris from infected plants and put it in the trash. For more information see the file on Controlling Fungal Disease