Soybean rust (SBR) is caused by the fungus Phakopsora pachyrhizi. Early symptoms of SBR following infection can be found in the lower soybean canopy and can be mistaken for a number of other common diseases of soybean. First symptoms are lesions that appear as small chlorotic and irregularly shaped spots appearing as early as five days after infection. The disease has been of particular concern to growers in the southern U.S. since first being detected in the continental U.S. in November 2004. Depending on the crop's growth stage and the developmental progress of the disease, SBR can cause significant yield losses unless effective management tactics, such as timely foliar fungicide applications, are employed.
The goal of this risk management tool is to help growers assess potential yield losses due to SBR and determine possible economic scenarios related to the decision to spray fungicides to protect the crop. Researchers at the University of Kentucky, Louisiana State University, Embrapa soja in Brazil, Kansas State University as well as a number of other Universities in the United States have worked together to develop and test a model based on our understanding of how SBR develops and damages a soybean crop and the economic benefits of mitigating these yield impacts. The tool calculates yield losses given your SBR epidemic scenario and soybean growth stage information and estimates the economic benefits of spraying based on cost of spraying and other related costs.
An Extension Plant Pathology Fact Sheet titled "Soybean Yield Loss Prediction Tool for Managing Soybean Rust" which summarizes information about tool development, limitations of the model and how to use the tool is available here.