This poinsettia was diagnosed with Pythium root rot and excess soluble salts. Plants had full root system that turned brown and collapsed. After being diagnosed, plants were watered with clear water to leach excess fertilizer from the roots and a fungicide was applied. These are the roots one week after watering with clear water. Notice the new white roots beginning to re-grow.
The close-up photo shows decayed roots. The outer root easily sloughs off when pulled with finger tips, leaving the inside strand of root (rat tail).