An Artificial Neural Network (ANN) is an approximate mathematical model that attempts to mirror biological neural network in its structure and functionalities. ANNs are useful for many engineering tasks such as optimization, prediction, function approximation, pattern recognition, and control. In this reseach an ANN was used to approximate a function that relates the Leaf Area Index (LAI) with the Leaf Area Duration (LAD). The objective was to predict how LAD effects the development of Asian Soybean Rust (ASR) and to evaluate the temporal dynamics of this disease.