Abstract: Fusarium graminearum causes wheat head blight disease and produce differentmycotoxins (as Deoxynivalenol=DON) which are toxic for human and animal. During off season itsurvives in the soil, on weeds and in crop residues. A 6 months study was conducted in controlledconditions (microcosms of natural soil, 17°C, 80%WHC) to test whether the presence of DON inthe wheat crop residues gives advantages to F. graminearum to survive and develop a primaryinoculum during the decomposition process. This study was carried out in the presence of the wholesoil biota (i.e. fungi, bacteria, protozoa, nematodes and earthworms). Both F. graminearum and thebiota were monitored during the decomposition process. The wheat crop residues were placed onthe soil surface or incorporated into the natural soil. This experiment was conducted with (1mgDON/kg soil-straw mixture) and without DON. This study suggested that the mycotoxins provideda competitive advantage to F. graminearum and were deleterious towards the fungal communityand the nematodes but not towards the bacteria or the earthworms. However, all the results were notstatistically significant. The use of molecular tools as well as the forthcoming quantification ofDON in the residues during 24 weeks of observation will provide the clarification and may confirmor not the trends we observed.