This study evaluated the use of pathogenic fungi in the biological control of barnyardgrass (Echinochloa crus-galli), which has been rated as the most serious weed in rice (Holm et al 1977). From 1997 to 1999, more than 10 pathogenic fungi were isolated from naturally infected barnyardgrass leaves collected from different rice-growing areas in China. Preliminary bioassays show that Exserohilum onoceras (EM) and Drechslera monoceras (DM) are the most pathogenic to barnyardgrass. Further evaluation of these fungi as biocontrol agents was also conducted.
Fungi cultured for 7 d on potato dextrose agar were used as seed inoculum. Conidia were mass-produced on a barnyardgrass seed solid substrate (Huang et al 1999). Three pieces of agar plugs from the margins of young colonies were transferred to sterilized substrates and then incubated at 28 °C in the dark. Conidia were harvested 14 d after incubation by shaking the flask with 50 mL of 0.05% Tween 20 distilled water, suspensions of which were filtered through a layer of cheesecloth. Conidia concentrations were determined with a hemacytometer.