In southern New South Wales the resumption of ley land for wheat growing has been accompanied by an increase in take‐all (Ophiobolus graminis) and Fusarium root rot (Fusarium culmorum). No such increase has been observed in foot and root rots of wheat caused byHelminthosporium sativum and Curvularia ramosa.It is shown experimentally that these differences are related to the relative capacity of the causal fungi to persist in wheat straw buried in each of two unsterilized soils which, because of past cultural treatments, differed in their organic carbon and total nitrogen content. While the saprophytic survival ofO. graminisandF. culmorumwas promoted by high soil fertility that ofH. sativumwas markedly depressed. The survival ofC. ramosawas little affected by soil fertility.F. culmorum, H. sativumandC. ramosaeach remained viable under the soil conditions best suited to their survival in one‐third to one‐half of the test straws for 2 years butO. graminiswas not recovered after the 52nd week of sam