Scarlet leaf spot of Stewartia spp. caused by Ramularia sp., a new disease

Abstract

Since 1997, a hitherto unrecorded disease has been observed on Stewertia pseudocamellia trees planted in Ibaraki, Saitama and Chiba Prefs. It occurred seriously in 2000 not only on S. pseudocamellia but also on S. monadelpha. Many small circular spots occur on leaves and they soon enlarge to 10-20 mm in sizes widely surrounded by scarlet or yellowish discoloration. Diseased leaves are successively defoliated. Lower surface of the spotted areas is covered with white powdery masses of conidiophores and conidia. Disease could develop on sound leaves by artificial inoculations spraying each of mycelial or conidial suspensions. For this disease on Stewartia, “scarlet leaf spot” is proposed as a new disease name. Causal fungus was tentatively identified as a species of the genus Ramularia Unger with the confused concept.