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Pythium Seed and Root Rot
Causal Agent:
Pythium spp.
Symptoms and Signs:
- Pre- and post-emergence damping off
- Water-soaked lesions on the roots, hypocotyls, or cotyledons
- Brown soft rot
- Plant death
Disease Cycle:
- Overwinters as oospores, or a thick-walled reproductive spore, in the soil. These spores can remain viable in the soil for several years.
- When soil is saturated, oospores germinate to eventually produce zoospores, or motile infective spores. Water is essential in the life cycle of Pythium.
- These spores swim to the root tissue and penetrate the plant cells. Oospores can also directly infect the plant root.
- The pathogen will then grow between cells of the plant, colonizing and deteriorating root tissue.
Disease Management:
Soil drainage: The most important factor in disease management of watermolds is proper soil drainage. The pathogen cannot exist in areas without persistent standing water. This is particularly important in fields using no-till practices.
Fungicide treatment: Currently there are several fungicide chemistries that are labeled for seed treatments to Pythium spp. However, it is important to note that the efficacy of these chemistries vary depending on the species. Currently, metalaxyl, mefenoxam, ethaboxam, oxathiopiprolin and the strobulurin chemistries are registered to control Pythium spp. For fields with a history of replant issues, a combination of at least two different chemistries targeting water molds is recommended.
Planting date: While planting date may not be an effective management strategy on its own, planting at times that optimize seed germination and seedling emergence will reduce losses. Avoid planting right before a major storm front or periods where rain is forecast for several days in a row. This is not always possible, but conditions where soil moistures are high for several days play a major role in the development of these infections.
Host resistance: There is partial resistance in soybean to many of the Pythium species that are expressed in the seed and/or the roots. More work is in progress to identify the key locations and develop markers to assist in the breeding of soybeans with resistance to this diverse group of Pythium spp.