PROBLEM TO BE SOLVED: To obtain a microbial herbicide capable of controlling Solidago serotina, manifesting excellent herbicidal activities to weeds and being used in combination with a chemical herbicide by including a specific microorganism as an active ingredient.
SOLUTION: This microbial herbicide contains microorganisms (e.g. Pseudomonas syringae SEI-1 strain) belonging to Pseudomonas syringae, and manifesting pathogenicity to Solidago serotina as an active ingredient. The concentration of the microorganisms is, for example, in the case of suspension, preferably 108-109 cells/ml. When the herbicide is used for the control of the Pseudomonas syringae, the agent is inoculated to the intact or injured Solidago serotina by one or more methods selected from coating, adherence and spraying. The agent can be used in combination with one or more kinds of chemical herbicides, and as a result, the number of uses of and the amount of the chemical herbicides can be reduced, and the reduction contributes environmental preservation.