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First Report of Anthracnose of Velvet Ash Caused by Discula fraxinea in Louisiana

December 1998 , Volume 82 , Number  12
Pages  1,401.2 - 1,401.2

G. E. Holcomb , Department of Plant Pathology and Crop Physiology, Louisiana Agricultural Experiment Station, Louisiana State University Agricultural Center, Baton Rouge 70803

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Accepted for publication 30 September 1998.

Velvet ash (Fraxinus velutina Torr.), a native tree of the southwestern United States, was commonly planted in Louisiana and other southeastern states until horticulturalists lost interest in the plant due to insect and disease problems. For several years, velvet ash trees in Baton Rouge have exhibited necrotic leaf spots and blotches during March and April. Trees frequently have 10 to 25% foliage infection and those most severely infected may show 50% defoliation. Small hyaline conidia that averaged 9.0 × 3.8 μm were produced in acervuli in necrotic tissue on lower leaf surfaces of affected trees. A fungus that produced similar conidia was consistently isolated from infected leaves and grown on potato dextrose agar. Pathogenicity tests were performed by misting 3 × 106 conidia per ml on leaf surfaces of velvet ash seedlings that were then placed in a dew chamber maintained at 26°C for 48 h. Chlorotic leaf spots developed on inoculated plants in 4 to 6 days at 24°C and were followed by necrotic spots and blotches 4 days later. The fungus was reisolated and identified as Discula fraxinea (Peck) Redlin & Stack (previously known as Gloeosporium aridum Ellis & Holw.) (2). Velvet ash anthracnose was first reported from California in 1949 (1), but this is the first report of its occurrence in Louisiana.

References: (1) D. M. Coe and W. W. Wagener. Plant Dis. Rep. 33:232, 1949. (2) S. C. Redlin and R. W. Stack. Mycotaxon 32:175, 1988.

© 1998 The American Phytopathological Society