"Chlorine dioxide was more effective against Aphanomyces sp. than S. diclina and A. bisexualis. Three days of immersion in chlorine dioxide >100 ppm inhibited hyphal growth of S. diclina and A. bisexualis, and concentrations >50 ppm inhibited growth of Aphanomyces sp. Immersion in 500 μg/ml chlorine dioxide for 1-4 h killed the hyphae and concentrations of 32 to 63μg/ml inhibited germination and killed zoospores of all three strains. The result suggest that treatment of hatchery water with 63μg/ml of chlorine dioxide for 10 min can control the zoospores but does not inhibit the growth of fungal hyphae of these strains. We conclude chlorine dioxide is an effective antifungal agent on both the hyphal and zoospore stages of S. diclina, A. bisexualis and Aphanomyces sp."