Abstract A description is provided for Phytophthora megasperma . Information is included on the disease caused by the organism, its transmission, geographical distribution, and hosts. HOSTS: On a wide range of hosts (inculding sugarcane, lucerne, soyabean, crucifers (Brussels sprouts, cabbage, cauliflower, kale, rutabaga, turnip), beet, carrot, spinach, potato), also in soil and plant debris in pond water. Phytophthora megasperma var. megasperma has been recorded on Althaea rosea, Brassica oleracea, Castanea sativa, Matthiola incana, Narcissus sp. and conifer soil; Phytophthora megasperma var. sojae on Asparagus officinalis, Brassica oleracea, Cicer arietinum, Glycine max, Medicago saliva, Melilotus spp., Prunus amygdalus, P. persica, Saccharum officinarum, Senecio cruentus, Solanum tuberosum and pond and soil water (Tompkins et al. , 1936, Herb. IMI). DISEASES: Causing seed-piece rot of sugarcane and a shoot rot of lucerne, soyabean and vegetables particularly crucifers (Brussels sprouts, cabbage, cauliflower, kale, rutabaga, turnip) as well as beet, carrot, spinach, and potato ('pink rot'). Infected plants wilt and their foliage may be discoloured red or purple at the leaf margins. DISTRIBUTION: Australasia (Australia, New Zealand, Tasmania); Europe (England, France, Ireland, Italy); North America (Canada, U.S.A.); South America (Argentina). (CMI Map 157, ed 2.) TRANSMISSION: Soil-borne and favoured by wet conditions with temperatures around 15-24°C. Persistence in soil for over 1 yr. is possible due to delayed germination of oospores (31: 394).