A Leaf Spot of Cucumber Caused by Ulocladium cucurbitae in New York. T. A. Zitter, Department of Plant Pathology, Cornell University, Ithaca, NY 14853. L. W. Hsu, Department of Plant Pathology, Cornell University, Ithaca, NY 14853. Plant Dis. 74:824-827. Accepted for publication 2 May 1990. Copyright 1990 The American Phytopathological Society. DOI: 10.1094/PD-74-0824.

Ulocladium cucurbitae, a leaf spot pathogen of cucumber (Cucumis sativus), was recovered from commercial fields and breeding plots in two widely separated areas of New York. The fungus was pathogenic to many commonly grown cucumber cultivars in the Northeast, including Poinsett 76, Marketmore 76, Sweet-Slice, Dasher II, Pacer, and Raider. In addition, Alternaria alternata was recovered from all of the lesions examined. In pathogenicity tests, only U. cucurbitae produced symptoms identical to those observed in the field. A. alternata failed to infect cucumber directly, but when plants were inoculated with a mixture of conidia of both fungi, A. alternata readily colonized the necrotic tissue produced by the U. cucurbitae infections. U. cucurbitae did not infect other cucurbits. Several isogenic cucumber lines bred for resistance to target spot, caused by Corynespora cassiicola, also showed excellent resistance to Ulocladium leaf spot.