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Utilization of a Multispectral Radiometer to Evaluate Fungicide Efficacy to Control Late Leaf Spot in Peanut. Forrest W. Nutter, Jr., Assistant professor, Department of Plant Pathology, University of Georgia, Athens 30602; R. H. Littrell(2), and T. B. Brenneman(3). (2)(3)Professor emeritus and assistant professor, respectively, Department of Plant Pathology, Coastal Plains Station, Tifton, GA 31793 Phytopathology 80:102-108. Accepted for publication 8 August 1989. Copyright 1990 The American Phytopathological Society.. DOI: 10.1094/Phyto-80-102.

Reflectance measurements were compared to visual assessment methods in 1985, 1986, and 1987 in Plains, GA, to measure fungicide efficacy for the control of late leaf spot caused by Cercosporidium personatum. Percent reflectance of 800-nm wavelength radiation was recorded from peanut canopies treated with different test fungicides by using a hand-held multispectral radiometer. In all but one case, percent reflectance increased in a linear fashion as visual disease assessments decreased. Analysis of variance and mean separation tests for visual versus remotely sensed assessments revealed that percent reflectance-based measurements had lower coefficients of variation than visually based assessment schemes. Higher coefficients of determination (R²) and lower standard errors of Y (pod yield) were obtained when percent reflectance values were regressed against Y compared to the R² values and standard errors obtained from regression equations employing visual assessments as the independent variable. Reflectance-based measurements were also faster and easier to obtain than visually based assessment methods. Percent reflectance values explained more of the variation in visual leaf spot assessments using a 1–10 rating scale compared to visual estimates of percent disease severity. Rank correlations for the ranking of fungicide treatments (based on the different assessment methods) with the rankings for pod yield revealed that reflectance-based assessments had a higher rank correlation with pod yield rankings than did visual assessment methods. Measurements of reflected radiation at 800 nm from peanut canopies can provide rapid, objective, and precise measurements to evaluate fungicide efficacy to control late leaf spot in peanuts.