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Bitter rot, caused by <i>Colletotrichum acutatum</i> and <i>C. gloeosporioides</i>, is a significant late-season disease of commercial apples. We identified four factors implicated in the Indiana bitter rot outbreaks of 2010 and 2011: cultivar susceptibility, weather conditions, fungicide spray schedules and fungicide resistance. Summer temperatures and rainfall exceeded the 30-year average by at least 1 degree Celsius and 2.5 cm, respectively, in both years. Review of spray records found that growers with losses to bitter rot did not use captan at the maximum-labeled rate and extended applications to the longest labeled interval. Isolates were obtained from fruit collected from three Indiana apple orchards to test whether fungicide resistance played a role in this outbreak. Thirty-five isolates from each orchard were screened for resistance to the fungicides kresoxim-methyl and thiophanate-methyl. Preliminary data suggest that 20% of the isolates were resistant at 0.2 ppm kresoxim-methyl, and 30% of all isolates were shifted in resistance. In 2 of the 3 orchards, 100% of the isolates were resistant to thiophanate-methyl; in the third, only 3% tested as resistant. These findings suggest that growers should modify their bitter rot management practices during seasons that are unusually hot and wet by using the maximum rate and shortest interval when applying captan while also recognizing the risk of resistance to strobilurin fungicides.<p><p>Keywords: Fungus, Fruits-Nuts, Apple