Abstract Each of 212 yellow-poplar sprout clumps studied had one live and one dead sprout. Butt rot was present in 26 percent of the living stems. Live stem ages ranged from 12 to 45 years. The dead sprout had died of suppression and its stage of decay rather than its size indicated the probability of butt rot in the associated live stem. A heartwood connection between the sprouts preceded the spread of decay from the dead sprout into the butt of the living stem. Pathological heartwood formed where stems were closely appressed and increased the area of heartwood contact between such stems. Vigor index, crown class, diameter, total height, and rate of radial growth of live stems were inversely related to butt rot incidence. Armillaria mellea and other Hymenomycetes were isolated from areas of white and brown rot in 11 of 56 live stems. Bacteria and Fungi Imperfecti, particularly Fusarium spp., Margarinomyces spp., and Trichoderma lignorum , were often isolated from discolored wood other than that showing white or brown rot. Management proposals based on experimental plot data should be considered applicable only on silviculturally similar areas. Removal of low-vigor sprout clumps or of suppressed stems of a clump before their diameter exceeds two inches is recommended on the basis of this study.