Abstract: The weed dayflower Commelina communis may be suppressed in the infection of Phoma herbarum. We studied the effects of fungal inoculum and host leaf stage on the infection of fungal strain SYAU-06. Experiments showed that inoculation with mycelial suspension at 1.03×10⁹ cfu/mL gave rise to infected leaf rate, disease index and fresh weight reduction at 91.16%, 74.26 and 53.35%, respectively. Inoculation with conidia and chlamydospore at the same inoculation concentration caused 56.62% and 41.58% infected leaf rate, 25.76 and 21.02 disease index, 15.39% and 11.96% fresh weight reduction. Perfect control of the weed with strain SYAU-06 was achieved by inoculation with mycelial suspension over 10⁷ cfu/mL before 3-leave stage and 7—9 days of culture time.