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Disease Detection and Losses

Powdery Mildew of Sugar Beet: Disease and Crop Loss Assessment. F. J. Hills, Extension agronomist, University of California, Davis; L. Chiarappa(2), and S. Geng(3). (2)Senior plant pathologist, FAO, Rome, Italy; (3)Associate professor of Agronomy and biostatistician, University of California, Davis. Phytopathology 70:680-682. Accepted for publication 18 January 1980. Copyright 1980 The American Phytopathological Society. DOI: 10.1094/Phyto-70-680.

Various disease control treatments were used to produce five sequences of disease development in each of three sugar beet field trials. Disease appraisal was accomplished biweekly by evaluating 25 mature leaves per plot as to the extent of leaf area diseased on a scale of 0 to 5 corresponding to 0, 10, 35, 65, 90, and 100% of the leaf area diseased. A season-long disease index was calculated for each disease control treatment as a weighted average of biweekly appraisals from disease onset to 1 October. The weighing factor was the number of weeks from evaluation date to 1 October. Season-long indexes correlated well with crop loss. The estimation of crop loss was improved by combining data over all years and including the yield of healthy plants in addition to the season-long disease index.