The pathogenicity of five Fusarium spp. frequently isolated from wheat and barley roots in southern Idaho was investigated during four growth-chamber experiments and two field studies. A real-time PCR assay for quantifying the presence of E culmorum from infected root tissue was also developed based on nucleotide sequence for the tri5 gene. Fusarium culmorum, followed by E acuminatum and E reticulatum, resulted in the largest root lesions and percent infected root area. However, E semitectum, followed by E acuminatum and E equiseti, had the greatest impact on total root length. The TaqMan-based real-time assay was able to quantify E culmorum in root tissue from both growth-chamber and field studies down to 61 pg. The assay also detected E pseudograminearum and E graminearum but could not distinguish among these three Fusarium spp.