First Report of Thyronectria austroamericana Canker on Thornless Honey Locust in North Carolina

Specimens from a thornless honey locust (Gleditsia triacanthos var. inermis 'Shade Master') with cankers were submitted in May 1999 to the North Carolina State University Plant Disease and Insect Clinic by staff from the North Carolina Zoological Park (Asheboro). Abundant stromata of Gyrostroma austroamericana, the anamorph of Thyronectria austroamericana, were associated with the cankers. A visit to the Zoological Park during August 1999 revealed seven additional honey locust trees with multiple branch and stem cankers and dieback. All infected trees had perithecia of T. austroamericana and/or its anamorph. The fungus is distinguished by the large clusters of yellow-brown perithecia with dark brown tips produced on stromata emerging from lenticels, elliptical muriform ascospores, and sparse ascoconidia (1,2). Ascoconidia form as the result of ascospores budding within the ascus. Other trees of the cultivar are an integral part of the landscaping theme of the African Pavilion of the park, and park staff were concerned about disease spread. Infected trees were 8 years old, and several had evidence of sunscald cankers, a common infection court of T. austroamericana (2). Thornless cultivars of honey locust are popular landscape plants in the central and eastern United States and may be seriously affected by T. austroamericana (2). Apparently 'Shade Master' is very susceptible to the fungus and should not be used as a landscape tree, especially where the disease has been reported. This is the first report of T. austroamericana in North Carolina on any host. Voucher specimens have been deposited in the National Fungus Collection, Beltsville, MD (BPI 74693), and in the Mycological Herbarium, Department of Plant Pathology, North Carolina State University, Raleigh. References: (1) E. V. Seeler, Jr. J. Arnold Arbor. Harv. Univ. 21:429, 1940. (2) W. A. Sinclair et al. 1993. Diseases of Trees and Shrubs. Cornell University Press, Ithaca, NY.