It is not found in soilless growing media but it is common in greenhouses, on floors and on the ground. When contamination occurs to the growing medium, Rhizoctonia rapidly colonizes the soil and causes root or crown rot. Leaves that touch the ground may also become infected. Like Rhizoctonia , Pythium has a broad host range. Pythium is often referred to as a water-mold because of its propensity to grow in water, and because it has unique swimming spores.
Pythium survives indefinitely in soil by producing oospores.
The oospores are stimulated to infect by germinating seeds and root exudates. High soil moisture and high fertility generally increase disease severity. Depending on the species of Pythium , high or low temperatures may be favored. Like Rhizoctonia , Pythium is soil-borne and is more of a problem in the greenhouse than in the field. In the field, Pythium can be a problem in wet soils, especially to transplants.