A Pythium species, most likely Pythium aphanidermatum was observed in the roots and stems of this garden chrysanthemum. Symptoms of Pythium vary according to temperature, moisture and the species of Pythium involved. The first symptom is often a wet, black basal rot which extends several inches from the soil surface. Affected plants wilt and collapse rapidly. Often the fungus invades leaves touching the soil and progresses into the stem at the node, causing a black lesion. In such cases, plants may not exhibit root and basal stem rot. Pythium is favored by high fertility and high moisture. Pythium is a natural inhabitant of the soil and can survive there indefinitely as well as in dirt and debris in greenhouses. Keep irrigation hose ends off the floor and avoid contaminating growing media with soiled hands, tools or flats. For more information and recommended fungicides see the New England Pest Management Guide or update message posted August 27, 2009.