Comparison of Chemical and Cultural Controls for Cercospora Blight on Asparagus and Correlations Between Disease Levels and Yield

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Abstract
The relationship between disease levels of Cercospora blight on ferns of four cultivars of asparagus during the summer and yield of asparagus during the following spring was investigated for a 3-yr period (1986-1989). The area under the disease progress curve (AUDPC) was used to describe overall disease levels. Five treatments: residue management before spear production in the spring either through tillage or burning, application of mancozeb or chlorothalonil fungicides to ferns during summer, and an untreated control were followed to attain disease levels. Disease progress curves showed that fungicides were most effective in delaying and reducing the levels of disease; however, burning of the residue also delayed disease for approximately 7 days and reduced total levels of disease compared to the control and tillage treatments. Applications of mancozeb or chlorothalonil fungicides to ferns during the summer resulted in greater yields than other treatments (P .ltoreq.s 0.05). Burning of fern residue increased yield compared to tillage and control treatments (P .ltoreq. 0.05). Tillage treatments had similar (AUDPC) values as the control but resulted in increased yields (P .ltoreq. 0.05). Linear regression analysis was used to determine the relationship between the amount of disease on asparagus ferns during the summer and the yield of marketable spears produced in the following spring. Coefficients of determination (R2) varied among the cultivars and years but accounted for 38-99% of the variation in yield. The amount of disease on the ferns was inversely correlated with yield. Slopes and intercepts varied within and among years. UC 157 cultivars had higher intercept and slope values than either Mary Washington or Viking, indicating a greater yield response from disease management practices. Residue management or the use of fungicides should be included in any integrated pest management system developed to reduce disease and maximize yield of asparagus.