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Disease Progress of Sclerotinia Wilt of Sunflower at Varying Plant Populations, Inoculum Densities, and Environments. Berlin D. Nelson, Department of Plant Pathology, North Dakota State University, Fargo, 58105; Doris M. Hertsgaard(2), and Renee C. Holley(3). (2)Department of Statistics, North Dakota State University, Fargo, 58105, Present address: D. H. Research, Box 5194, Fargo, ND, 58105; (3)Department of Plant Pathology, North Dakota State University, Fargo, 58105, Present address: Dekalb-Pfizer Genetics, Dekalb, IL, 60115. Phytopathology 79:1358-1363. Accepted for publication 29 June 1989. Copyright 1989 The American Phytopathological Society. DOI: 10.1094/Phyto-79-1358.

Disease progress of Sclerotinia wilt of sunflower, caused by Sclerotinia sclerotiorum, was studied in varying plant populations over eight sites with different inoculum densities. Two prominent characteristics of disease progress were the absence of disease symptoms during the first 4060 days after planting and the wilting of most plants after anthesis (~75 days after planting). Analysis of disease progress with the Weibull model showed that plant population affected the rate of disease progress, but no consistent relationship between these factors was found. Lower plant populations, for example, did not consistently have lower or higher rates of disease progress. The differences in rates of disease progress between plant populations had no apparent effect on seed yield. Rates of disease progress were positively correlated with inoculum density, but not with precipitation and temperature (as growing degree days).

Additional keywords: Sclerotinia sclerotiorum, epidemiology, soilborne diseases.