Crown Rot Causing Sudden Wilting and Death on Ajuga (Bugleweed)
Sudden wilting, yellowing and death of ajuga, also known as bugleweed, means crown rot may have invaded the planting.
This fungal disease is most common in warm wet or humid weather. It first appears as sudden wilting and dieback in colder climates and yellowing and death of plants in warmer areas. The stems of infected plants turn brown or black and rot.
This disease can be introduced into the garden on infected plants or soil or spread by tools and water. Since the disease is in the soil it is difficult to eradicate.
Remove and destroy infected plants and the surrounding soil immediately. Be sure to disinfect your tools with a one-part bleach and nine-part water solution during and after the process.
If the disease continues to spread or has destroyed much of the planting, it is time to start over in a new location with disease-free plants.
A bit more information: Reduce the risk of crown rot to healthy plantings by thinning groundcover plantings every few years or before they become overcrowded. And avoid planting crown rot susceptible plants in the bed where the Ajuga died. Consider amending the soil with compost, peatmoss or coir to improve drainage before planting.