Abstract
This experiment was made to confirm that winter killing of grasses are caused mainly by freezing injury and Sclerotinia snow blight disease over winter in Nemuro-Kushiro district. Orchardgrass, meadow fescue, perennial ryegrass, tall fescue and timothy were used and sown on the field plots in July 1974 (volcanic ash soil). Lower temperatures were induced by removing snow cover and Sclerotinia snow blight disease was controlled by sterilization. The results obtained were as follows: 1) Soil surface temperature had been kept nearly 0℃ under snow cover not controlled and had been cooled often to -15〜-20℃ under snow cover removed during winter (Dec. 1974〜Apr. 1975). 2) Of the species used, the hardest was timothy with following order: tall fescue, meadow fescue>orchardgrass>perennial ryegrass and of the variety, Canadian ecotypes were more resistant to cold than the others. 3) Dead stubble percent was increased mainly by freezing injury under snow cover removed and it was increased by Sclerotinia snow blight disease under snow cover not controlled. The varieties sensitive to cold or becoming feeble under snow cover were susceptible to Sclerotinia snow blight disease, with only a few exceptions. 4) From the results mentioned above, in this district, it was considered that winter killing occurred due to freezing injury under less snow condition and occurred due to Sclerotinia snow blight disease under heavy snow condition.
