As seedlings mature, they become more resistant to attack, and disease may be limited to crown and root tissue. When plants are placed into an infested soil, the fungus is stimulated by substances released from the plant roots. The growth of Pythium is favored by wet soil conditions. Disease is most severe when the soil is wet for prolonged periods of time or when the temperature is too high or too low for optimal plant growth. Plants that are stressed or that are overly succulent are more susceptible to attack.
Pythium is also a problem in locations where the same crop is planted year after year.
Since there is no simple way to distinguish between these fungi in the field, samples of infected plants should be submitted to a plant diagnostic laboratory for positive identification. Diagnosticians identify root and crown rot fungi by looking for fungal structures in plant tissues under a microscope and by growing these fungi on culture media. In addition, there are commercially available detection kits that use antibodies to detect Pythium in affected plant tissue. Successful disease management requires an approach that utilizes preventive cultural practices. Commercially available soilless mixes are usually free of pathogens and do not require treatment before use.