Over 560 isolates of Fusarium were collected from 121 wheat and corn fields in Michigan and identified to species level. While F. graminearum comprised 82% of recovered isolates, members of the Fusarium tricinctum complex were also identified in nine fields of wheat. In corn, members of the Fusarium fujikuroi species complex comprised 50% of isolates recovered. The largest proportion were F. subglutinans (33.3%). F. awaxy, a species not yet reported in corn in the U.S., was identified in six fields, comprising 4.6% of the collection. Isolates of F. graminearum collected were also genotyped to determine the type of trichothecene mycotoxins they produce. The large majority, 413 isolates (92%) were the 15-acetyldeoxynivalenol (15-ADON) type and twenty-six (6%) were 3-acetyl-deoxynivalenol (3-ADON). In addition, seven isolates (1.5%) were classified as the NX-2 chemotype. Interestingly, most of the NX-2 and 3-ADON isolates were found in the same region, from five fields in the far norther eastern part of the state with less intensive agricultural land use. 

In vitro sensitivity to triazole chemistries registered in the United States (metconazole, tebuconazole, and prothioconazole) were assessed with mycelial growth assays. Isolates were most sensitive to metconazole, and less sensitive to prothioconazole and tebuconazole. Species-specific differences in sensitivity were uncovered, with FTSC members significantly less sensitive than F. graminearum, and FFSC significantly more sensitive.  All EC₅₀ values were below 4 µg/mL for F. graminearum, and sensitivity between the three chemistries was highly correlated. A small portion of isolates within F. graminearum had EC50 values 10-fold greater than sensitive isolates. A field trial was established to investigate sensitivity in vivo with eight isolates of differing in vitro sensitivities. No differences in fungicide efficacy were observed.  While there may not be practical resistance in Michigan currently, monitoring should continue as there is variation in in vitro sensitivities present within and among species of Fusarium. A subset of F. graminearum isolates were also tested for pydiflumetofen sensitivity. Mycelial growth EC50 values ranged from 0.008 to 0.263 μg/mL, with a mean of 0.060 μg/mL. EC50 values for spore germination assays ranged from 0.167 to 0.538 μg/mL, with a mean of 0.321 μg/mL

Source: Management and characterization of fungal diseases in Michigan wheat. PhD Thesis. M Breunig