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Disease Note.

Sorghum Downy Mildew on Sweet Corn in Central Illinois. J. K. Pataky, Department of Plant Pathology, University of Illinois, Urbana 61801. N. R. Pataky, and D. E. Fisher. Department of Plant Pathology, University of Illinois, Urbana 61801, and Del Monte Research Center, P.O. Box 9004, Walnut Creek, CA 94598. Plant Dis. 74:183. Accepted for publication 7 November 1989. Copyright 1990 The American Phytopathological Society. DOI: 10.1094/PD-74-0183E.

Sorghum downy mildew, caused by Peronosclerospora sorghi Weston & Uppal, was found in Fulton County, Illinois, in an 80- ha field of sweet corn (Zea mays L. 'Excellency' and Del Monte variety 20-35) that had been double-cropped after wheat. "Half-leaf" and "strap-leaf" symptoms and conidia on the underside of leaves were observed. Incidence of systemically infected plants varied in the field from 0.5 to 90% and averaged 10-15% for the entire 80 ha. Oospores were found in leaves that were soaked in water for 48 hr. Sorghum downy mildew also was found on a wild species of sorghum growing as a weed in adjacent fields, 50-80 m from the sweet corn. The infected Sorghum sp. may have been a source of conidia that caused systemic infection of sweet corn seedlings, or soilborne inoculum (oospores) may have increased on the weed host when the 80-ha field was planted to soybeans the previous year. P. sorghi occurs on corn in southern regions of the United States (1,2), but this report is the first of which we are aware of P. sorghi causing a significant amount of disease on sweet corn in central Illinois. 

References: (1) M. C. Futrell et al. Plant Dis. Rep. 54:311, 1970. (2) H. L. Warren et al. Plant Dis. Rep. 58:430, 1974.