The objective of this study was to identify sources of on-farm inoculum of Clavibacter michiganensis subsp. michiganensis (CMM), the causal agent of bacterial canker of tomatoes. Two hundred ninety seven samples from inanimate (swabbing from walls, floor, wood, hoses, etc.) and animate sources (weeds, other plants, tomatoes) from 3 commercial greenhouses were tested to see if they carried the CMM pathogen. A wide variety of methods were utilized in attempts to conclusively identify the bacteria, including an agglutination kit and a commercial diagnostic testing service that used a quick ELISA test. Any bacteria isolated that were likely to be the pathogen were further tested to see if they could cause disease on tomatoes. The various isolation procedures were cumbersome, slow, expensive, and difficult to interpret since none were diagnostic alone. The disease organism is difficult to isolate, identify conclusively, and even more difficult to prove to cause disease.