Airborne Remote Sensing to Detect Greenbug Stress to Wheat

Vegetation indices calculated from the quantity of electromagnetic radiation reflected from plants measured using multi-spectral imaging systems have been used to quantify stress levels in plants. Greenbugs, Schizaphis graminum (Rondani), cause stress to wheat, Triticum aestivum L., plants and therefore multi-spectral remote sensing may be useful for detecting green bug-infested wheat fields. The objectives of this study were to assess whether variation in light reflectance from plants infested with varying densities of greenbugs could be detected and quantified using airborne imagery obtained with a multi-spectral digital camera mounted in a fixed-wing aircraft. In a replicated experiment where greenbug density was manipulated in 1-m(2) plots of two winter wheat varieties ('Jagger' and 'OK 101') planted in a 1 ha field, we found that wheat infested with greenbugs exhibited a similar reflectance response for the two varieties. Both varieties showed a reduction in the normalized differenced vegetation index (NDVI) as greenbug density increased, as indicated by a negative slope for the regression of NDVI on greenbug density. Neither slopes nor intercepts differed significantly between the two varieties. A second vegetation index, Green NDVI, was not consistently correlated with greenbug density in the experiment. In a second experiment in large plots in four production winter wheat fields we found significant negative correlations between greenbug density and the vegetation indices for three of the four fields. The results indicated that airborne multi-spectral imaging can be used to detect stress caused by greenbug infestation of wheat fields.