Strobilurins, such as Pyraclostrobin (Headline), is a commonly used group of fungicide across the World. It has in Europe shown to increase biomass production, delay leaf senescence, and improve stress tolerance in wheat plants in absence of foliar pathogens. A number of physiological processes associated with these positive developmental responses have been documented in wheat and tobacco plants treated with Strobilurins. Because these processes are common to other crops, it is possible that Strobilurins could be used strategically to increase yield in other crops, such as soybean [(Glycine max L.) Merrill]. Limited information exists in the literature on strobilurins effect on soybean growth and plant development. It is therefore our hypothesis that applying Headline to soybean is going to change soybean growth and development. Our objective is to determine the effect of Headline on soybean yield and grain composition in the absence of foliar diseases. Foliar diseases will be controlled by using a triazole fungicide (Folicur) in combination with Headline. Research will be conducted at 2 locations in Iowa in 2005 and 2006. The experimental design is a randomized complete block in a split plot arrangement with 3 replications. Main plot will be four varieties and the split plot will be ten treatments (control, Folicur, Headline, Folicur + Headline applied at R1, R3, and R5). Starting at R1 leaf area index and chlorophyll meter readings will be measured weekly to evaluate rate of senescence and defoliation among cultivars and fungicide treatments. At harvest, 0.76 m² will be hand harvested from each plot to determine the yield components among the different treatments. Data from the 2005 growing season will be presented in the poster.