Fungicide Sensitivity of Colletotrichum cereale Isolated from Turfgrasses in the Northeastern United States

Twenty-seven isolates of Colletotrichum cereale collected from the northeastern United States between 1993 and 1995 and twenty-three isolates collected in 2007 were screened for resistance to fosetyl-Al, chlorothalonil, polyoxin-D, iprodione, fludioxonil, triadimefon, azoxystrobin, and thiophanate-methyl. The comparison between isolates collected from 1993 to 1995 to isolates from 2007 demonstrated significant increases in EC50 values for azoxystrobin, polyoxin-D, thiophanate-methyl, and triadimefon. Significant increases in EC90 were observed for all fungicides except chlorothalonil and fosetyl-Al. Both EC50 and EC90 values for chlorothalonil decreased significantly between the two sampling periods. Most importantly, our results indicate that the occurrence of C. cereale isolates resistant to azoxystrobin and thiophanate-methyl has increased in the Northeast over the past 12 to 14 years based on the isolates tested and that overall resistance to some commonly used turf fungicides has increased as reflected in significantly higher average EC50 and EC90 values.