Cercospora Leaf Spot of Crape Myrtle, Lagerstroemia indica

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Plant Pathology Circular No. 171, October 1976
Fla. Dept. Agric. & Consumer Services
Division of Plant Industry

S. A. Alfieri, Jr.

Crape myrtle, Lagerstroemia indica L., is a deciduous shrub, attaining a height of 10 to 20 ft, with smooth brown bark and white, pink, or red flowers occurring in clusters. It is found as an introduction in the American tropics and in the southeastern United States but is native to Asia and northern Australia. The genus Lagerstroemia contains approximately 30 species in south and east Asia and Australia (1).

Cercospora lythracearum Heald & Wolf is the causal fungus of a leaf spot on Lagerstroemia indica (2,3). In Florida the leaf spot disease was severe in 1976, especially on the pink-flowering variety 'Near East'. Of the 3 flowering varieties utilized in landscape plantings in Gainesville, it was noted that 'Near East' was the most susceptible in terms of greatest leaf infection and defoliation. The red or lavender variety was less susceptible, and the white flowering variety or 'Far East' least susceptible with only a very few Cercospora lesions on the leaves. Heavy infections with Cercospora can cause severe defoliation with a debilitating effect on the plant.

Fig. 1. Cercospora leaf spot of crape myrtle beginning as tiny flecks on lower surface of 4 uppermost leaves and large irregular, brown spots coalescing and causing distortion of the larger lower leaves on the right.

The leaf spots incited by Cercospora lythracearum are distinct, dark brown, irregular, and up to 5 mm in diameter with no yellow margin. Spotted leaves become distorted, losing their flat, smooth appearance (fig. 1), particularly as the spots enlarge and coalesce. Leaf spots on the lower surface of the leaves are initiated as tiny brown flecks with no visible spotting on the upper surface of the leaves. As leaf spots enlarge, they appear on both sides of the leaf and coalesce; the leaf turns yellow, and the brown spots persist with a green border of green leaf tissue, which stands out in sharp contrast to the yellowed leaf. At this stage heavy defoliation occurs.

Reference to University of Florida/IFAS Pest Control Guides

Contribution No. 422, Bureau of Plant Pathology, P. O. Box 1269, Gainesville, FL 32602.

Literature Cited

1. Bailey, L. H. 1954. Manual of cultivated plants. MacMillan Co., New York. 1116 p.

2. Chupp, C. 1953. A monograph of the fungus genus Cercospora. Cornell Univ., Ithaca, N.Y. 667 p.

3. Heald, F. D., and F. A. Wolf. 1911. New species of Texas fungi. Mycologia 3:5-22.

4. McGuire, J. M., A. E. Einert, and D. M. Barber. 1975. Controlling powdery mildew and Cercospora leaf spot of crape myrtle with fungicides. Arkansas Farm Res. 24(1):14.