VIEW ARTICLE

Techniques

Detection and Measurement of Plant Disease Gradients in Peanut with a Multispectral Radiometer. Forrest W. Nutter, Jr., Assistant professor, Department of Plant Pathology, University of Georgia, Athens 30602; Phytopathology 79:958-963. Accepted for publication 28 April 1989. Copyright 1989 The American Phytopathological Society. DOI: 10.1094/Phyto-79-958.

Point and line sources of Cercosporidium personatum were established in peanut field plot experiments in Plains, GA, in 1986. Disease gradients were quantified by measuring percent leaflet defoliation with respect to distance from the sources and by measuring percent reflectance of 800-nm wavelength radiation off the crop canopy with a hand-held, multispectral radiometer. There was a linear relationship between percent reflectance values and percent defoliation estimates for both point and line source experiments. There was also a linear relationship between percent reflectance values and yield (kg/ha) along the late leaf spot gradient in the line source experiment (R² = 98.2%). Disease severity gradients of peanut rust foci were also quantified and compared to percent reflectance values by using linear regression analysis. Percent reflectance values, when used as the independent variable, explained 94.6–96.5% of the variation in peanut rust disease severity along rust gradients. Reflectance of sunlight from peanut canopies at 800 nm provided a rapid and objective measurement of disease intensity and the amount of green leaf area contributing to pod yield. Recording percent reflectance offers a means to quantify the benefits obtained from disease control tactics aimed at protecting and maintaining healthy green leaf area from the effects of plant pathogens.