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Dicotyledonous Weeds as a Source of Fusarium oxysporum Pathogenic on Soybean. J. B. Helbig, Former Graduate Student, Department of Plant Science, University of Delaware, Newark 19711. R. B. Carroll, Associate Professor, Department of Plant Science, University of Delaware, Newark 19711. Plant Dis. 68:694-696. Accepted for publication 13 February 1984. Copyright 1984 The American Phytopathological Society. DOI: 10.1094/PD-68-694.

Twenty-one dicotyledonous weeds were studied for their potential role in Fusarium blight of soybean, a disease of increasing importance in the Delmarva region. Isolations were made from root and stem tissue of 800 weed plants collected throughout the growing season from conventional tillage and no-tillage soybean fields at 20 locations. Fusarium oxysporum was obtained from 16 weed species. No direct relationship to tillage practice was noted. Sixteen of 17 isolates of F. oxysporum from weeds were pathogenic on the soybean cultivar Essex under greenhouse conditions. No symptoms of F. oxysporum infection were observed in weed plants collected from the field or when inoculated in the greenhouse with a soybean isolate. Common dicotyledonous weeds in soybean fields can serve as symptomless hosts of the blight pathogen, which retains pathogenicity for soybean.