Verticillium wilt is one of the most devastating pathogens affecting Mentha spp. currently. The development of resistant mint cultivars remains the best option to combat the costly effects of this disease on the industry. While low levels of Verticillium wilt resistance have been observed, resistance is neither fully characterized nor incorporated into mint cultivars. We developed an effective disease assay as well as a symptom scoring rubric to evaluate variation in Verticillium wilt resistance in a tetraploid spearmint mapping population, bred peppermint population, and ?-irradiated peppermint population. Variation in symptom onset, progression of disease, and symptom severity was observed in all populations, however, resistance was only identified in the spearmint and bred peppermint populations. No ?-mutant lines showed acceptable levels of resistance. Disease severity and timing was described through the calculation of the area under the disease progress curve for each genotype that proved to be an effective indicator of mean final score of a genotype. The infection process was visualized through the use of a GFP tagged V. dahliae strain in order to better elucidate a possible mechanism of resistance in mint. Overall, a possible mechanism could not be identified and the sampling protocol needs further optimization to determine the resistance mechanism.