Geotrichum citri-auranti, sour rot of citrus, causes economical crop losses on Satsuma mandarin and lemon in Turkey. Because the usage of guazatine was restricted in packinghouses, new solutions are required to minimize these pathogens. Thirty-two isolates of G. citri-auranti were collected from packinghouses in Ege and the Mediterranean Region and tested against fungicides. In this project, we examined the old postharvest fungicides; guazatine, thiabendazole (TBZ) and imazalil against G. citri-auranti and new generation postharvest fungicides such as pyrimethanil, fludioxonil and azoxystrobin at different doses in vitro and in vivo. We also studied sensitivity of pathogen isolates against fungicides in vitro. All of the isolates were found resistant to imazalil and TBZ even high doses of fungicides. It was found that 28% of isolates were sensitive to guazatine and 72% resistant. Both in vitro and in vivo tested azoxystrobin did not affect pathogen growth and decay development. Only guazatine was effective on pathogens growth and decay development. In vivo tests conducted on Satsuma mandarin showed that a combination of sodium bicarbonate (2%) and guazatine (900 mu g/ml) and their combination were the most effective treatments for disease development.