A recent sample of Verbena cv. Valley Lavender from propogation stock showed stunting, poor root formation, and plant death. Roots were light brown and failed to grow beyond the original plug. The problem was diagnosed as root rot caused by the fungus Thielaviopsis basicola.
The above photos shows chlamydospores in crushed root tissue under magnification - this a characteristic diagnostic sign of T. basicola infection.
For more detailed information on Thielaviopsis root rot and management, check out this article in Greenhouse Product News.