Cercospora Blight Development on Asparagus Fern and Effects of Fungicides on Disease Severity and Yield. Kenneth E. Conway, Associate Professor, Department of Plant Pathology, Oklahoma State University, Stillwater 74078. James E. Motes, Bruce Bostian, Christine G. Fisher, and P. L. Claypool. Professor, Department of Horticulture and Landscape Architecture, Oklahoma State University, Stillwater 74078; Superintendent, Vegetable Research Station, Bixby, OK 74008; Former Graduate Student, Department of Plant Pathology, and Professor, Department of Statistics, Oklahoma State University, Stillwater 74078. Plant Dis. 71:254-259. Accepted for publication 2 November 1986. Copyright 1987 The American Phytopathological Society. DOI: 10.1094/PD-71-0254.

Disease progress of Cercospora blight of asparagus was studied in field plots, using an assessment system developed to estimate disease on asparagus ferns during 1984 and 1985. Logistic and Gompertz models were compared for goodness of fit for linear regression of disease proportions in fungicide-treated and control blocks for cultivars UC 157 F₂ and Mary Washington. Gompertz models fit the data better according to standard error of estimate values, but neither model fit all data. Rates of increase of disease were significantly lower in chlorothalonil blocks. Areas under the disease progress curves (AUDPC) were determined from untransformed percent disease values and were significantly less in fungicide treated blocks. Reducing the in-row density of crowns did not significantly reduce disease progress rates or AUDPC. Conidial densities of Cercospora asparagi were monitored with a Kramer-Collins 7-day spore sampler. Large increases in conidial densities occurred from mid-August through October during 1982–1985; however, disease in control blocks was estimated to be 72–94% by 1 September. Protection of ferns by fungicides was correlated to yield increases in UC 157 F₂ blocks during 1982–1985 and in Mary Washington in 1985.