Foliar Blight and Branch Dieback of Container-Grown Giant Redwood in California Caused by Phytophthora citrophthora. C. M. Sandlin, Department of Plant Pathology, University of California, Riverside 92521. D. M. Ferrin, and J. N. Kabashima. Department of Plant Pathology, University of California, Riverside 92521, and University of California Cooperative Extension Service, Anaheim 92805. Plant Dis. 75:1074. Accepted for publication 24 June 1991. Copyright 1991 The American Phytopathological Society. DOI: 10.1094/PD-75-1074A.
A foliar blight and branch dieback of giant redwood (Sequoiadendron giganteum (Lindl.) Buchholz) was observed on trees maintained under overhead irrigation at a nursery in Orange County, California, in November 1990. Phytophthora citrophthora (R.E. Sm. & E.H. Sm.) Leonian was isolated from diseased woody tissue plated on water agar. Koch's postulates were fulfilled by inoculation of foliage with zoospores (2 X 106 spores per tree) and subsequent reisolation of the pathogen from diseased tissue. Lesions first developed at the tips of needles and at the junctures of small twigs and branches of inoculated trees maintained in a mist chamber. Lesions then expanded to larger twigs and branches, causing dieback of healthy foliage above the newly infected tissue, thus reproducing field symptoms. Additionally, abundant sporangia formed on the surface of diseased foliage in the mist chamber. The combination of blue-black lesions bordered by healthy green tissue below and dead brown foliage above is characteristic of the disease.