Fusariosis is one of the most important problems encountered in maize crops in Belgium and it is responsible for significant losses (up to 30%) in both grain yield and quality. More than 7% of the world cultures are destroyed by fusariosis (Hoffmann and Schmutterer 1999 ; Papst et al., 2005). Fusariosis is in fact the result of simultaneous contaminations by several Fusarium species, mostly F. graminearum, F. verticillioides and F. proliferatum. Other species are also detected at low frequencies, such as F. avenaceum, F. subglutinans, F. sambucinum, F. sporotrichioides, F. crookwellense, F. culmorum, F. poae. Furthermore, recent studies suggest that a wider diversity than that already known could exist within some species or species complex. For example, F. graminearum has been recently subdivided in nine phylogenetic species (O’Donnell et al., 2004) ; the Gibberella fujikuroi species complex (containing F. verticillioides) was subdivided in at least 46 phylogenetically species from which 10 sexual species (Leslie and Summerell, 2006). Some of those Fusarium species are able to produce mycotoxins, potentially responsible of human and animal health diseases. Important amounts of those mycotoxins are often found in maize silages, causing health problem for the livestock. Nevertheless, it is established that the physico-chemical properties existing in silages (pH, aerobiose, t °) prevent the growth of Fusarium spp. (Scudamore and Livesey, on 1998). Mycotoxins are thus produced in the field. The present project aims to understand the dynamics of the various Fusarium species development during the cultural season in Belgium, the genetic variability within species, as well as their mycotoxin production. Two partners are associated with BCCMTM/MUCL to the present project supported by the Région Wallonne **: The CARAH (Centre Agronomique de Recherches Appliquées du Hainaut) and the CIPF (Centre Indépendant de Promotion Fourragère, UCL) who are in charge of field assays.The CARAH team also performs the mycotoxin ...