Using digital image analysis and spectral reflectance data to quantify damage by greenbug (Hemitera: Aphididae) in winter wheat

The usefulness of digital image analysis and spectral reflectance data to quantify damage by greenbugs (Schizaphis graminum (Rondani)) was evaluated for two winter wheat (Triticum aestivum L.) fields, three field experiments, and one greenhouse experiment in Oklahoma and Texas. A hyperspectral field spectrometer and a digital camera were used to record reflectance and to acquire images over 0.25-, 0.37-, and 1-m(2) greenbug-damaged wheat canopies. A large number of spectral vegetation indices compiled from the literature were calculated and relationship to damage by greenbugs was investigated. The mean percent damage by greenbugs estimated through digital image analysis varied from 13 +/- 1/0.25 to 73 +/- 7/0.37 m(2). The mean greenbug abundance ranged from 191 +/- 22/0.25 to 54,209 +/- 7908/0.37 m(2). Correlation analyses showed strong associations between damage by greenbugs in wheat and spectral vegetation indices. Correlation coefficient ranged from 0.82 to -0.98. These results suggest that remote sensing using spectral reflectance and digital images can be nondestructive, rapid, cost-effective, and reproducible techniques to determine damage by greenbugs in wheat with repeatable accuracy and precision. Together with the existing spectral indices, two versions of a new index algorithm are suggested in this paper. (c) 2006 Elsevier B.V. All rights reserved.