Experiments were performed to determine effects of supplementation of cottonseed hull/sawdust substrate with Mn, Cu, and ground soybean on yield, mushroom size, and bacterial blotch resistance of two commercial strains of Pleurotus eryngii. A basal formulation (d.w.) of cottonseed hulls (62%), aged red oak sawdust (27%), whole ground soybean (6%), corn distiller's waste (4%) and calcium sulfate (1%) was supplemented to 50, 150 or 250 microg/g Mn or Cu and to 4%, 8% and 12% whole ground soybean. The cottonseed hulls content in the basal substrate was adjusted to compensate for the addition of ground soybean. Formulated substrates were mixed, placed in 1050ml bottles, and sterilized at 121 degrees C for 90min. Mushroom yields were significantly higher from substrates containing Mn at 50 microg/g and soybean at 8% and 12% supplementation compared to the basal substrate. As the level of soybean addition to substrate increased, yield also increased. The addition of Mn at levels of 150 and 250 microg/g significantly enhanced yield as well, although less than did the 50 microg/g treatment. To assess the influence of mushroom strain and substrate composition on blotch disease severity, pilei of P. eryngii were inoculated with Pseudomonas tolaasii. Strain WC888 was more resistant to disease than WC846. Disease severity was greater when substrates were amended with Cu to 150 or 250 microg/g. There was a significant difference in inherent levels of Cu in the basidiomata of different strains, but P. eryngii did not accumulate Cu and disease severity was not correlated with Cu content of the basidiomata.