Leaf Spot of Southern Magnolia Caused by Pseudomonas cichorii. J. M. Mullen, Extension Program Associate-Plant Pathology, Alabama Cooperative Extension Service, Auburn University, Auburn 36849. G. S. Cobb, Superintendent, Ornamental Horticulture Substation, Alabama Agricultural Experiment Station, Mobile 36608. Plant Dis. 68:1013-1015. Accepted for publication 25 July 1984. Copyright 1984 The American Phytopathological Society. DOI: 10.1094/PD-68-1013.

A new leaf spot of southern magnolia (Magnolia grandiflora) was found to be caused by Pseudomonas cichorii. Newly unfolded leaves had dark brown lesions covering as much as two-thirds of the leaf area. Symptoms were less severe on older foliage. Pathogenic bacterial isolates from M. grandiflora matched P. cichorii in morphology and physiological and biochemical test results. M. grandiflora, M. macrophylla, M. soulangeana, and M. tripetala developed foliar lesions after artificial inoculation. Sprays of tri-basic copper sulfate (2.4 g/L) or copper hydroxide (1.2 g/L) applied at weekly intervals during periods of active shoot growth suppressed disease. Disease severity was less with ground-level irrigation than with overhead irrigation.