Influence of Host Resistance and Crop Rotation on Initial Appearance of Potato Early Blight. D. Shtienberg, Department of Plant Pathology, Cornell University, Ithaca, NY 14853. W. E. Fry, Department of Plant Pathology, Cornell University, Ithaca, NY 14853. Plant Dis. 74:849-852. Accepted for publication 9 March 1990. Copyright 1990 The American Phytopathological Society. DOI: 10.1094/PD-74-0849.

The effects of host resistance, frequency of potato cropping, and previous crop on the initial appearance of potato early blight (caused by Alternaria solani) were evaluated under natural infestation in upstate New York. Initial lesions were observed at the same time on cultivars resistant to early blight and on those susceptible to early blight. Initial lesions on the current crop occurred earlier if the preceding crop was potato or tomato. In these fields, the earliness of lesion appearance was not affected by the previous frequency of potato production. However, if the preceding crop was not potato or tomato, more frequent potato production was associated with earlier occurrence of first lesions. The previous crop and the frequency of previous potato production were associated with an earlier appearance (6–8 days) of initial lesions. The application of these findings to the scheduling of sprays for early blight suppression is discussed.