Association of Common Ragweed with Sclerotinia Rot of Cabbage in New York State. H. R. Dillard, Assistant Professor, Department of Plant Pathology, New York State Agricultural Experiment Station, Cornell University, Geneva 14456. J. E. Hunter, Professor, Department of Plant Pathology, New York State Agricultural Experiment Station, Cornell University, Geneva 14456. Plant Dis. 70:26-28. Accepted for publication 23 July 1985. Copyright 1986 The American Phytopathological Society. DOI: 10.1094/PD-70-26.

Sclerotinia rot of cabbage caused by Sclerotinia sclerotiorum was observed in the field in close association with a known susceptible weed host, common ragweed (Ambrosia artemisiifolia). Ragweed flower parts and whole plants were infected with S. sclerotiorum and bridged the infection to cabbage. In laboratory tests, ascospores of S. sclerotiorum infected male ragweed flowers and fruits, and cabbage leaves became infected when in contact with these infected tissues. Ragweed pollen alone served as a substrate for S. sclerotiorum but only resulted in leaf infections of cabbage when present in large clumps. Ascospores did not infect ragweed or cabbage leaves without an exogenous food base.