Resistance of Honeylocust Cultivars to Thyronectria austro-americana. W. R. Jacobi, Associate Professor, Department of Plant Pathology and Weed Science, Colorado State University, Fort Collins 80523. . Plant Dis. 73:805-807. Accepted for publication 15 May 1989. Copyright 1989 The American Phytopathological Society. DOI: 10.1094/PD-73-0805.

Three cultivars (Imperial, Skyline, and Sunburst) and one selection (thornless) of honeylocust (Gleditsia triacanthos var. inermis) were screened for resistance to the canker fungus Thyronectria austro-americana. Whether inoculated in fall or spring, the thornless selection produced significantly smaller cankers and formed callus and closed inoculation wounds twice as fast as any cultivar. Imperial and Skyline were similar in susceptibility, and Sunburst was the most susceptible. Partial mechanical girdling had little effect on canker expansion, but girdling Sunburst trees in the fall resulted in 40% mortality whether or not they were inoculated. Cankers induced by two isolates of T. austro-americana on Skyline and Imperial cultivars and on the thornless selection differed significantly in size.