This plant was diagnosed with Pythium root rot. Signs of Pythium root rot fungi on poinsettias are wilting and stunting. Roots are soft and decayed, sometimes extending up into the stem where it causes a canker. Botrytis can also develop on the stem causing a canker. Looking closely, the rotted outer covering of the root slips from the central core. There are several species of of Pythium that can cause problems on poinsettias .
Pythium is a natural inhabitant of the soil and can survive there indefinitely as well as in debris in the greenhouse. Growers having re-occurring problems with Pythium , should review their overall production practices including fertilizing, watering and media handling. Over-watering and excessive fertilizer levels promote Pythium . Good sanitation is crucial for prevention. Keep hose ends off the floor and avoid contaminating growing medium by cleaning areas where plants are held, media is handled and plants are potted.
Suspicious plants can be diagnosed through your University diagnostic lab or through a private diagnostic lab.
For more information on Pythium see the New England Recommendation Guide .