Root Rot of Aucuba japonica Caused by Phytophthora cinnamomi and P. citricola and Suppressed with Bark Media. Suzanne Spencer, Former Graduate Student, Department of Plant Pathology, North Carolina State University, Raleigh 27650. D. M. Benson, Associate Professor, Department of Plant Pathology, North Carolina State University, Raleigh 27650. Plant Dis. 65:918-921. Accepted for publication 27 July 1981. Copyright 1981 American Phytopathological Society. DOI: 10.1094/PD-65-918.

Phytophthora cinnamomi and P. citricola were pathogenic to Aucuba japonica in laboratory and greenhouse studies. P. citricola was isolated more often than P. cinnamomi from diseased aucubas in landscape plantings and caused a more severe root rot that often resulted in death of the plant. Root rot was suppressed in well-drained pine bark (pH 4.5) and hardwood bark compost (pH 6.8) but not in a soil-sand medium after 10 days. Suppression was lost if media were kept saturated and the pH of pine bark was raised to 6.5 with lime; however, saturated pine bark at pH 4.5 remained suppressive. An apparently nonpathogenic root rot with symptoms similar to those caused by Phytophthora spp. developed when aucuba plants were grown in poorly drained soil amended with cornmeal (1–10% by weight).

Keyword(s): Cornaceae, drowning, gold-dust plant, woody ornamental.