The effects of fungicides on soil fungal populations

Abstract

Four fungicides, Captan, Dicloran, Thiram and Verdasan were applied at 28-day intervals for 12 consecutive months and their effects on soil fungal numbers and the incidence of individual species were studied. Immediately after application, these fungicides reduced the number of fungal propagules in soil by 23, 11, 36 and 50% respectively compared with control. Captan- and Dicloran-treated soils were rapidly recolonised within 7 days of the application of fungicides. The effects of Thiram and Verdasan were more persistent: the fungal numbers in soils treated with these fungicides did not recover sufficiently to reach control levels throughout the sampling period. Fewer species of fungi were isolated from Thiram- and Verdasan-treated soils than from Captan- and Dicloran-treated soils. Chrysosporium pannorum (Link) Hughes was the principal species isolated from Verdasan-treated soil and the fungus was isolated in increased numbers immediately after application of Verdasan than on subsequent sampling days. Cladosporium cladosporioides (Fres.) de Vries, Mortierella minutissima van Tiegh, Trichocladium asperum Harz, Trichoderma hamatum (Bon.) Bain, and Zygorhynchus moelleri Vuill. were found to be generally tolerant of all four fungicides. However, Botryotrichum piluliferum Sacc. and Marchai, Gliocladium roseum Bain., Humicola fusco-atra Traaen, Sepedonium chrysospermum (Bull.) Link ex Fr., and Trichoderma viride Pers. ex Fr. were generally intolerant of the fungicides but rapidly recolonised the treated soils. While the concentrations of Captan and Dicloran used were fungistatic to T. viride, Thiram and Verdasan were fungicidal.