The effects of fungicides on Fusarium spp. and Microdochium nivale and their associated trichothecene mycotoxins in French naturally-infected cereal grains

Chemicals applied to wheat at the flowering stage are used to reduce yield losses associated with Head Blight (HB) and trichothecene contamination of infected grains. Efficacy of fungicide treatments at anthesis were assessed against Fusarium spp. ( Fusarium graminearum, F. avenaceum, F. poae, F. culmorum and F. tricinctum were the most frequent Fusarium species) and Microdochium nivale and on Fusarium mycotoxin concentration over three years on naturally infected fields of soft wheat, durum wheat and barley. Deoxynivalenol (DON) and nivalenol (NIV) were the most frequently detected mycotoxins. Treatments including azoxystrobin significantly decreased M. nivale infection levels, while infection levels of F. graminearum and F. culmorum were unaffected. Treatments that included metconazole or tebuconazole significantly decreased F. graminearum or F. culmorum infection levels, but the effect was variable across the years and type of fungicide applied. In 2002, DON concentration in wheat treated with tebuconazole and metconazole was reduced by 46% and 48%, respectively, while NIV concentration was unaffected. Yet, in 2000 and 2001, significant reduction in F. graminearum or F. culmorum infection levels were not always associated with significant reductions in DON and NIV mycotoxins. The fungicides we applied in naturally infected fields did not always reduce mycotoxin producers or alternatively the trichothecenes produced. Different explanations for this phenomenon are discussed.