Evaluation of annual and herbaceous perennial plants for susceptibility to Phytophthora root and crown rot in the Southeastern United States

Annual and herbaceous perennial ornamental bedding plants are popular, high value crops in the southeastern United States. However, many of these plants are subject to root or crown rot caused by Phytophthora species. In North Carolina, Phytophthora nicotianae Breda de Haan, Phytophthora drechsleri Tucker, Phytophthora cryptogea Pethybr. & Laff., and/or Phytophthora tropicalis Aragakia and J.Y. Uchida cause this disease in greenhouse production systems and in the landscape. Because practical management options for landscapers and homeowners are limited, the objective of this study was to identify annual and herbaceous perennial ornamental landscape plants that perform well in Phytophthora-infested landscape beds at three locations in western and central North Carolina. Although landscape beds were artificially inoculated with P. nicotianae, P. drechsleri, P. cryptogea sensu lato, and P. tropicalis, P. nicotianae was the most frequently isolated species from symptomatic plants and was the only species confirmed to be active at all locations in both years of this study. Eighteen cultivars of annuals and twenty-one cultivars of herbaceous perennials performed well and have been recommended for Phytophthora-infested landscapes to growers and homeowners in the southeastern United States.