Effect of Nitrogen Concentration in Juvenile Foliage of Rhododendron on Phytophthora Dieback Severity. H. A. J. Hoitink, Professor, Department of Plant Pathology, The Ohio State University, Ohio Agricultural Research and Development Center, Wooster 44691. M. E. Watson, Head, Research Extension Analytical Laboratory, The Ohio State University, Ohio Agricultural Research and Development Center, Wooster 44691, and W. R. Faber, Assistant Professor, Agricultural Technical Institute, The Ohio State University, Wooster 44691. Plant Dis. 70:292-294. Accepted for publication 3 October 1985. Copyright 1986 The American Phytopathological Society. DOI: 10.1094/PD-70-292.

Nitrogen concentration in juvenile foliage of rhododendron cultivar Roseum Elegans was significantly and positively correlated with size and number of lesions caused by Phytophthora cactorum. Low numbers of tiny lesions were produced on nitrogen-deficient plants with concentrations of 0.7% in juvenile foliage. High numbers of large lesions that killed plants were produced on plants with nitrogen concentrations of 1.8–2.5% in juvenile foliage. Adding nitrogen to low-fertility plants on which small lesions had developed resulted in an increase in lesion size and eventual plant death.