This week precipitation has been mixed in northeast Illinois, areas north of the Rte. 80 corridor have received multiple rainfall events while areas south have received limited to no precipitation. Soy continues to progress, reaching R5, beginning seed stage. Depending upon variety maturity and planting date, most corn fields visited were R3-R4 to R4-R5. An unwelcome discovery this week was significant Tar spot symptoms in several corn fields. The decision on using a fungicide treatment is difficult in later maturity stages, especially when we are near R5, the dent stage. A reminder that grain fill in the dent stage often extends to 30 days or more. However, with declining commodity prices farmers need to consider their ROI (return on investment) when considering a or additional fungicide applications. A tool available to aid in the decision making is the Corn Fungicide ROI Calculator from the Crop Protection Network. The purpose of the Corn Fungicide ROI Calculator is to share results from university uniform corn fungicide trials conducted in the United States and Canada and allow farmers and others in the agricultural industry to calculate the potential return on investment (ROI) for corn fungicide application across a variety of user-defined factors, which is based on research data included in this calculator. The two variables needed are expected corn yield and marketing price. The calculator can be accessed at https://cropprotectionnetwork.org/fungicide-roi-calculator