Soybean rust (SBR) causes accelerated defoliation.  The impact on yield depends on the extent of the defoliation as well as the growth stage when it occurs.  Currently available models based on % leaf loss have not been fine tuned for late reproductive development.  These models are also less accurate than using a measure of the remaining LAI.  The use of NDVI to estimate remaining green leaf area is a promising tool.  Progress to date will be reported.