WeedSOFT is a decision support system that brings together a wealth of information on weed biology and management efficacy to improve weed management decision-making (Neeser et al. 2004). An essential part of maintaining WeedSOFT as the state-of-the-art weed management tool is validation and improvement of the crop yield loss model in the ADVISOR module. One of the most novel aspects of the crop yield loss model is the use of an adjusted competitive index (ACI) whereby the competitiveness of a given weed species is adjusted by a competitive index modifier (CIM) based on relative weed and crop growth stages (Tables 1 and 2). In this manner, weeds that emerge at the same time as the crop are considered more competitive than weeds that emerge at a later crop growth stage. The weed CI values are speciesspecific and differ among the several state versions of WeedSOFT due to regional differences in weed competitiveness. However, the CIM matrix is constant among crops and weed species.