Abstract A description is provided for Phyllactinia dalbergiae . Information is included on the disease caused by the organism, its transmission, geographical distribution, and hosts. HOSTS: On Dalbergia sissoo and other species of Dalbergia (Patil, 1962; Patwardhan, 1962, 1966; Pirozynski, 1965). DISEASES: Powdery mildew of sisam. This is the commonest powdery mildew found in India. GEOGRAPHICAL DISTRIBUTION: Chiefly India and Pakistan but also known from China and Japan and other Asian countries. TRANSMISSION: By wind-borne conidia and by cleistothecia which overwinter on the detached decaying leaves.