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Ecology and Epidemiology

Incidence of Verticillium nigrescens in Soybeans. S. J. Vesper, Department of Plant Pathology, University of Georgia, College of Agriculture Experiment Stations, Georgia Station, Experiment 30212; J. T. Turner, Jr.(2), and D. V. Phillips(3). (2)(3)Department of Plant Pathology, University of Georgia, College of Agriculture Experiment Stations, Georgia Station, Experiment 30212. Phytopathology 73:1338-1341. Accepted for publication 20 April 1983. Copyright 1983 The American Phytopathological Society. DOI: 10.1094/Phyto-73-1338.

Verticillium nigrescens was isolated from soybean flowers and from pods at several stages of development at eight locations in Georgia during 1977- 1981. The incidence in pods ranged from 0 to 36%, was highest 3- 5 wk after initial pod set, and declined gradually toward maturity. The highest incidence of the fungus in soybean pods occurred in fields where cotton had been grown repeatedly. The fungus was readily isolated from soil and high soil moisture levels were related to increased infection. Although other weed species were examined, the pathogen was isolated only from Solanum carolinense. When surface-sterilized pods were plated, V. nigrescens frequently grew from the end of the pedicel and only rarely grew from other parts of the pod. The fungus never caused vascular discoloration or wilt symptoms, but its presence was associated with decreased numbers of pods on infected plants. In growth chambers, V. nigrescens significantly reduced numbers of pods per plant and the weight of seed in inoculated plants. In the field, benomyl application reduced pod infection by 50- 90% and treated plants produced more pods than control plants.