Effects of temperature and dew period on sporulation of a mycoherbicide, Epicoccosorus nematosporus, on the lesion of its host, Eleocharis kuroguwai were determined. Conidia formation was first observed after 10 days on plants incubated for either 12 or 16 h in a dew chamber at 28℃; 16 h dew period resulted in more conidia formation. As the dew period was decreased to less than 8 h, fewer conidia formed. Conidial production was most abundant at 28℃ and produced as much as 3.3×10(4) conidia per lesion, while 0.1×10(3) and 2.3×10(3) conidia per lesion were produced at 16× and 36℃, respectively. Alternating temperature regimes, i.e., 30/15, 30/20, 28/20, and 28/15℃ (day/night) were much better than constant temperature, i.e., 30/30, 28/28/, and 20/20oC for sporulation. In the second sporulation, there were as much as 3.1×10(4) conidia per lesion (ca. <50% of the first sporulation). Then, sporulation dropped sharply to 6.2×10(2) conidia per lesion in the third sporulation. Results of this study suggest that temperature combined with dew period is the primary limiting factor in the use of E. nematosporus as a mycoherbicide of E. kuroguwai.