Garden Pests and Diseases: Bug or disease affecting lower half of plants?, 1 by Cheryl_103

Cheryl_103 wrote:
I've had this problem with different plants over the last few years; most are multi-stemmed perennials like this lavender.
The plants start off good and strong in the early spring, but then the lower leaves get dark and mushy-looking and die back. Although it doesn't kill the plant, it does seem to set it back and keep it from thriving.
We did have an excessively wet spring this year. Is it a fungus, or bug, or what? I would.like to be prepared next year if it's something I can treat.