Field studies were conducted during the 2010 and 2011 growing seasons along the Texas Upper Gulf Coast region to study the effects of fungicides on soybean disease development and to evaluate the response of four soybean cultivars to prothioconazole plus trifloxystrobin and pyraclostrobin. In neither year did any soybean diseases develop enough to be an issue. Only NKS 51-T8 responded to a fungicide treatment in 2010 while HBK 5025 responded in 2011. Prothioconazole plus trifloxystrobin increased NKS 51-T8 yield by 23% in 2010 while in 2011 the yield of HBK 5025 was increased 14% over the unsprayed check. No yield response was noted with pyraclostrobin on any soybean cultivar. Only prothioconazole？+？trifloxystrobin applied to either NKS 51-T8 or DP5335 in 2010 resulted in a net increase in dollars per hectare over the unsprayed check of the respective cultivar. In 2011, under extremely dry conditions, all fungicides with the exception of prothioconazole？+？trifloxystrobin applied to HBK 5025 resulted in a net decrease in returns over the unsprayed check. 1. Introduction Fungicide applications and timing have been shown to be critical for the control of foliar diseases on soybean [1]. The control of frogeye leaf spot (Cercospora sojina) varied with applications of benomyl at different reproductive stages of the crop [2]. To manage soybean rust (Phakopsora pachyrhizi) with fungicides, three strategies include applying fungicides in a predetermined calendar-based schedule, scouting and applying fungicides after the first detection of soybean rust or utilizing a forecast system that monitors disease development in areas that are potential inoculum sources, and applying fungicides ahead of a predicted deposition of spores [1, 3–5]. The older chemistry of foliar fungicides for soybeans included contact fungicides which remain on the leaf surface and if a rain event occurred soon after application, the fungicide could be washed off [6]. With improved chemistry, systemic fungicides are now available and these types of fungicides are absorbed by the leaves and move within the treated plant [6]. Systemic fungicides allow growers to properly manage soybean diseases now more than ever before. Soybeans that have been sprayed with a fungicide retain their leaves for a longer period of time, allowing the pods to fill and increase the size and weight of the beans [6]. Three of the newer fungicides include prothioconazole, trifloxystrobin, and pyraclostrobin. Prothioconazole is a sterol biosynthesis inhibitor fungicide in the triazolinthione class of fungicides [7] that
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