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Factors Affecting the Effectiveness of Sclerotia of Typhula idahoensis as Inoculum. Roy M. Davidson, Jr., Research Assistant, Department of Plant Pathology, Washington State University, Pullman 99163, Present address of senior author: Western Washington Research and Extension Center, Puyallup 98371; G. W. Bruehl, Professor, Department of Plant Pathology, Washington State University, Pullman 99163. Phytopathology 62:1040-1045. Accepted for publication 30 March 1972. DOI: 10.1094/Phyto-62-1040.

Sclerotia of Typhula idahoensis were more effective in inciting snow mold of winter wheat when placed on the soil surface than when buried 0.5 or 1.0 cm in soil, and were not effective when buried 2, 5, or 10 cm in soil. Incorporating up to 80% coarse sand in the soil mixture did not affect the above results. When 37, 75, 150, 300, 625, 1,250, and 2,500 sclerotia/kg of soil were mixed randomly within four different soils, the disease ratings and sclerotium production were the same in each of the soils. Disease severity increased with inoculum density up to 300 sclerotia/kg of soil and leveled off; sclerotium production increased with inoculum density up to 1,250 sclerotia/kg of soil. More sclerotia per infected plant were produced at 0.5 than at 0.5 C. The percentage germination of sclerotia was higher on acidified cornmeal dextrose agar than on rinsed river sand with no exogenous nutrients, and was higher on sand at 10 than at 3 C. When a dark fungus, believed to be Cladosporium herbarum, emerged from the sclerotia, T. idahoensis was seldom obtained.