To obtain rough blue grass having excellent insect resistance and disease resistance by artificially inoculating the rough blue grass with artificially propagated symbiotic bacteria and causing symbiosis to infect the rough blue grass with these bacteria, thereby introducing the symbiotic bacteria into the rough blue grass.

The symbiotic bacteria, such as Acremonium sp. Po-060 (FERM P-15862) consisting of mold associating in plant, are separated and are artificially propagated. The rough blue grass belonging to a Poa subfamily are artificially inoculated with these artificially propagated symbiotic bacteria. The symbiosis of the rough blue grass with the artificially inoculated symbiotic bacteria is caused to infect the rough blue grass with these bacteria, by which the introduction of the symbiotic bacteria to the rough blue grass is executed. The artificial inoculation of the rough blue grass with the conidia of the symbiotic bacteria is more preferable.