To control the infection of a plant with pathogenic microorganisms causing disease in the plant through soil by scattering a specific compound as an infection controller against soilborn disease on the soil around the plant.

A compound containing a pyridinium group of formula I [R is a (substituted) benzyl, a 1-18C alkyl, an allyl, an aryl or the like; X is a halogen] as a structural unit, or a pyridinium type compound such as formula II [R1 is a (substituted) benzyl, a 1-18C alkyl, an allyl, an aryl or the like; R2 is H, a 1-3C alkyl, a (substituted) benzyl, an aryl or the like; the ratio of (m) to (n) is (5:95)-(95:5)] is scattered as an infection controller of soilborn disease on the soil around a plant.