Measuring Herbicide Injury to Soybeans (Glycine max) Using a Radiometer

Abstract

Light reflectance from soybean foliage was compared to visual evaluations for assessing soybean injury caused by postemergence-applied paraquat and glyphosate. Coefficients of variation and of determination from multiple linear regressions for both herbicides indicated that reflectance was better correlated with injury measured by changes in leaf number, leaf weight, and stem weight than visual evaluations. Correlation coefficients among radiometer readings taken by different individuals were ≥0.98 for both herbicides. Correlation coefficients among visual evaluators ranged from 0.69 to 0.96 and from 0.74 to 0.94 for plots treated with paraquat and glyphosate, respectively. Light reflectance measured with a radiometer may be useful in evaluating injury from herbicides that cause chlorosis, necrosis, or defoliation of the target species.