Asian soybean rust (Phakopsora pachyrhizi H. Sydow & Sydow) has spread throughout Asia, Australia and into Africa and arrived in the southern United States in the fall of 2004.  This disease has the capacity to reduce soybean yields by up to 80%.  There are effective fungicides however, they are expensive and several applications may be necessary for disease control.  By not taking control measures, producers risk crop losses, while use of multiple fungicide applications may result in net economic losses.  Knowledge of the potential yield loss caused by this pathogen maybe used to improve management decisions such as, if and when control measures are required. In an on-going study with national and international collaborators, the role of rust-induced defoliation injury on soybean yield loss is being studied. The objective of this study is to determine the nature of the disease-crop interaction and determine whether the crop is differentially sensitive to this pathogen based on crop developmental stage.