Effect of plant age and cottony snow mold on winter survival of forage grasses

The low temperature basidiomycete (LTB, syn. Copribus psychromorbidus Traquair), the causal agent of cottony snow mold, is a major constraint to forage grass survival and productivity in the parkland region of the Canadian prairies under prolonged snow cover (e.g., 160 d). Studies were conducted to establish the level of the snow mold resistance in seven grass species commonly grown in western Canada and to identify the seeding dates that permit grass plants to develop maximum levels of resistance to snow mold. Following attack by the LTB fungus, considerable variation in winter survival and forage yield was observed among the grass species. Smooth brome and meadow brome were most resistant, followed by timothy and creeping red fescue. Tall fescue and orchardgrass were the most susceptible. Controlled-environment and field studies demonstrated that orchardgrass seeded in late spring resulted in greater winter survival and dry matter yield than when seeded in July or August, both in snow mold inoculated and noninoculated treatments. Additional mortality and dry matter yield loss were linked to snow mold injury. These results demonstrated that snow mold injury could reduce winter survival and yield in first-year forage grasses, especially in orchardgrass, and early seeding could reduce the impact of winter stresses. Key words: Grass, orchardgrass, timothy, smooth bromegrass, meadow bromegrass, creeping red fescue