Red raspberry plants were subjected to waterlogging after inoculation with different species of Phytophthora isolated from field outbreaks of root rot. The commonest species, a form of P. megasperma, was highly pathogenic to raspberry whether the plants had been waterlogged or not, but waterlogging increased the severity of disease caused by other species. P. cambivora and P. drechsleri were moderately pathogenic and non-pathogenic, respectively, in non-waterlogged conditions but killed plants that had been waterlogged for 4 d. P. megasperma var. megasperma required longer periods of waterlogging to cause severe symptoms and did not kill plants. Root rotting of waterlogged and non-waterlogged plants was controlled with a matalaxyl and copper mixture. The results indicate that several species of Phytophthora may contribute to poor growth and death of raspberries grown in poorly drained sites.