Dicotyledonous Weeds as a Source ofFusarium oxysporumPathogenic on Soybean

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Abstract
Dicotyledonous weeds (21) were studied for their potential role in Fusarium blight of soybean, a disease of increasing importance in the Delmarva [Delaware, Maryland and Virginia, USA] 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 fieds at 20 locations. F. 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 ''Essex'' soybean 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.