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Plant Pathology Circular No. 167, June 1976
Fla. Dept. Agric. & Consumer Services
Division of Plant Industry
S. A. Alfieri, Jr., and J. J. McRitchie
Southern magnolia, M. grandiflora L., is a stately evergreen tree occurring extensively in landscape ornamental plantings in the South. It has large, dark green, glossy, leathery leaves and showy white fragrant flowers. Southern magnolia has a fairly extensive growth range throughout the southeastern region of the United States, from Central Florida along the eastern coastal plain to New York, along the Gulf coast to Texas, and up to the southern portion of Illinois. It thrives best, however, in hot, humid climates.
Foliage diseases of M. grandiflora are relatively few in number and are not considered destructive. However, they can detract from the aesthetic value of the tree. Phyllosticta magnoliae Sacc. is a leaf-spotting fungus occurring occasionally on M. grandiflora. Other than descriptions of the fungus occurring on this tree (2,3), the literature available on this disease is sparse (1,4,6).
SYMPTOMS. The leaf spots are first observed as minute purplish black lesions on the upper surface of the leaves. The spots enlarge to 1 to 3 mm in diameter and the center becomes dirty white in color. These lesions are delimited by a prominent purple-black border and a faint chlorotic halo. As the leaf spots enlarge to approximately 20 mm they tend to become subcircular, with a less prominent dark margin and no chlorotic halo (fig. 1).
Fig. 1. Phyllosticta leaf spot of Magnolia
grandiflora L.:
A) Various stages of leaf spot development; B) enlargement of the
same leaf spots.
CONTROL. If the spotting caused by Phyllosticta magnoliae warrants control, periodic applications early in the growing season with copper fungicides would aid in controlling this disease (5).
Reference to University of Florida/IFAS Pest Control Guides
Contribution No. 417, Bureau of Plant Pathology, P. O. Box 1269, Gainesville, FL 32602.
Literature Cited
1. Edson, H. A. 1936. Diseases of plants in the United States in 1935. Plant Dis. Reptr. Suppl. 96:115-289.
2. Ellis, J. B., and B. M. Everhart. 1900. North America Phyllostictas. Gus E. Smith, Vineland, N.J. 76 p.
3. Grove, W. B. 1935. British stem- and leaf-fungi. Vol. 1. Cambridge Univ. Press, London. 488 p.
4. Martin, G. H. 1925. Diseases of forest and shade trees, ornamental and miscellaneous plants in the United States in 1923. Plant Dis. Reptr. Suppl. 37:347-446.
5. Pirone, P. P., B. O. Dodge, and H. W. Rickett. 1960. Diseases and pests of ornamental plants. The Ronald Press Co., New York. 776 p.
6. Rhoads, A. S. 1944. Survey of observations on plant diseases in Florida during the emergency plant disease prevention project surveys, July 25 to December 31, 1943. Plant Dis. Reptr. Suppl. 148:262-276.
