Abstract
The Cercospora causing brown leaf spot of Physocarpus spp. in Japan was identified as C. spiraeicola Muller et Chupp on the basis of their identical morphological characteristics. Among the inoculated plants belonging to Spiraeaceae, the fungus infected Physocarpus amurensis and P. opulifolius, but not Spiraea spp., Stephanandra spp. and Sorbaria kirilowii, even though, C. spiraeicola had been described on Spiraea prunifolia. Conidia of the fungus overwinter on the fallen diseased leaves. They keep well their germination ability throughout winter and serve as the primary infection source from May to June. Incubation period of the fungus is about two months in spring and one month in summer and early autumn. The fungus may not overwinter within winter bud on the diseased bushes. Conidia germinate and mycelial colonies grow at 10∼35C with optimum temperature of 25∼30C. They germinate well under atmospheric humidity above 98%. H-ion concentration has no influence on not only germination of conidia except pH 3, but also growth of mycelial colonies. Colonies of the fungus grow well on malt extract, potato-sucrose, Saito's soy and Waksman's solution agar.
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