Soil Fungicides for Controlling Chytridiaceous Mycoparasites of Gigaspora margarita and Glomus fasciculatum.

The percentage of azygospores of Gigaspora margarita with zoosporangia of chytridiaceous fungi (CF) was reduced significantly after agitating them in fenaminosulf before incubation in soil. Fenaminosulf did not affect zoosporangia development on chlamydospores of Glomus fasciculatum. Metalaxyl and ethazol were not effective against CF on spores of either mycorrhizal fungus. Azygospores of G. margarita were treated with fenaminosulf and used as the inoculum for pot cultures. After 19 weeks, the percentage of azygospores containing CF was reduced significantly by this treatment, whereas root colonization and sporulation by the mycorrhizal fungus were unaffected. Pot cultures of G. margarita, either drenched with fenaminosulf or not, did not differ in the percentage of azygospores containing CF. However, root colonization and sporulation by the mycorrhizal fungus was temporarily delayed when pots were drenched with fenaminosulf.