By this time, soils are usually cooler and wetter, and dormancy with new seed is no longer a problem. Recent research has shown that the age of winter wheat seed may have a significant impact on the seedling tolerance to infection by the Pythium fungus. Cook suggests that growers consider using high quality, current-year seed if seeding dates are late September or later, when cool, wet soils are often encountered. Background on Pythium Research by Cook and other plant pathologists over the past 10 years has shown that Pythium root rot can be a major production constraint for winter wheat in Northwest cropland areas receiving at least 16 inches annual precipitation. Where Pythium populations in the soil were experimentally reduced or nearly eliminated, yield typically increased 15 to 20 percent and sometimes up to 50 percent.
Pythium is a parasitic, water-mold fungus which favors cool, wet soil conditions.
It often attacks wheat shortly after planting by infecting the embryo of the seed as germination begins. The germinating embryo of the seed is ideal tissue for Pythium infection because it is young, growing tissue relatively unprotected by secondary cell wall thickening or cuticle development. Actual seed decay is generally only a few percent. Generally, seed-reserve nutrients and energy should be adequate for normal seedling development through this early stage. The embryo and region of root-shoot transition is also a source of hormones essential to normal seedling development, Any hormonal disturbance can affect seedling growth.