Stem blight can be mistaken for root rot caused by Rhizoctonia , which can also develop black stem lesions. However, stem lesions from root rot infections do not contain the tiny black pycnidia. Infected plants should be removed from the bed. Thinning of vinca beds and reduction of overhead shade will help reduce stem blight. Ajuga is subject to one major disease, crown rot, caused by the fungus Sclerotium rolfsii .
Crown rot is favored by the warm, humid weather typical of Kentucky.
In early stages of the disease, infected ajuga may show yellowing of lower leaves. Plants soon wilt and die because the causal fungus has invaded the roots and crown and cut off the water supply. Badly infected plants may be easily pulled up because the roots and crown have been destroyed. Circular patches of dead plants appear, especially in poorly drained beds. The most revealing diagnostic feature is the presence of small spherical tan to reddish brown sclerotia of the fungus.