To provide the subject method characterized by repelling/preventing algae/bacteria adhered to laver under culture through soaking for <1 min the laver with a treatment liquid containing 0.2-0.5 wt.% of fumaric acid and ≥0.35 wt.% of acetic acid and/or hydrochloric acid.

This method comprises soaking laver under culture with a treatment liquid containing 0.2-0.5 wt.% of fumaric acid and 0.35-1.00 wt.% or greater of acetic acid and/or hydrochloric acid for <1 min to repel bacteria such as reddish-brown scab bacteria and/or algae such as diatoms parasitic on the laver.