Technical Abstract: Brassica species and related plants produce glucosinolate compounds, which break down in soil to produce volatile sulfur compounds that are toxic to many soil organisms. Several Brassica crops used in crop rotations and as green manures have been associated with reductions in soilborne pests and pathogens. Selected Brassica crops, including canola, rape, oilseed radish, turnip, yellow mustard, and Indian mustard, were evaluated for control of various soilborne potato pathogens and diseases in culture, greenhouse trials, and field trials on commercial potato farms. In in vitro assays, volatiles released from chopped leaf material of Brassica crops inhibited growth of a variety of soilborne pathogens of potato, including Rhizoctonia solani, Phytophthora erythroseptica, Pythium ultimum, Sclerotinia sclerotiorum, and Fusarium sambucinam, with Indian mustard resulting in nearly complete inhibition (80 to 100%). All Brassica crops and barley reduced inoculum levels of Rhizoctonia solani (20-60% reduction) relative to a potato crop, and radish, rape, and Indian mustard reduced subsequent potato seedling disease by 30-85% in greenhouse tests. In on-farm trials at sites with substantial disease problems, Indian mustard, rape, and canola grown as a green manure rotation crop reduced powdery scab by 15-40% and black scurf by 50-85%, and Indian mustard reduced common scab by 25% in the subsequent potato crop relative to a standard oats or ryegrass rotation crop. These results indicate that Brassica crops have potential for use in the control of powdery scab, Rhizoctonia disease, and other soilborne disease problems.