Abstract: The spore germination method was used to determine the toxicities of tebuconazole,mancozeb and hymexazol to Physoderma maydis,and field trials were conducted to ascertain the effects of mancozeb 800 WP,430 g/L tebuconazole SC and hymexazol 700 WP on pathogenicity,as well as control efficacy when applied at 8-leaf stage of corn by spray.The results showed that mancozeb exhibited great inhibition to the germination of the resting sporangia of P.maydis,with the EC50 value of 66.71 mg/L,while tebuconazole and hymexazol had little effects.The pathogenicity was effectively lowered by the treatments of mancozeb and tebuconazole,which suppressed the occurrence of corn brown spot below the ear leaf and increased the content of chlorophyll,net photosynthetic and root activity.The control efficacy of mancozeb and tebuconazole against P.maydis were 91.31% and 88.99% respectively,which resulted in an increased yields of corn by 13.8% and 11.5% ,comparing with that of CK.