Technical Abstract: Bacterial root rot of sugarbeet caused by Leuconostoc mesenteroides subsp. dextranicum is a disease problem recently described in the United States. To ameliorate the impact of bacterial root rot on sucrose loss in the field, storage piles, and factories, studies were conducted to establish an assay for identifying host resistance. In 2006 and 2007, 21 commercial cultivars were grown, hand dug, and tested in a petri dish laboratory assay. Root slices were inoculated with L. mesenteroides, incubated at 30°C, and the diameter of the rotted area was measured after 72 and 96 hr. The cultivars were tested in a randomized complete block design with 4 replications. When averaged over both studies, root rot after 96 hr in the commercial cultivars ranged from 14 to 37 mm, while the least significant difference was 5 and 7 mm in 2006 and 2007, respectively. The cultivar ranking between studies was correlated at 72 (r squared = 0.47, P = 0.03) and 96 (r squared = 0.43, P = 0.05) hr. The assay allowed for reliable cultivar separation regardless of whether one, two, three, or four roots were used per replication. The assay should allow host resistance to bacterial root rot to be improved in sugarbeet.