Maximising control with fungicides of Fusarium Ear Blight (FEB) in order to reduce toxin contamination of wheat

Abstract

Fusarium ear blight (FEB) constitutes a disease complex involving toxin producing species (e.g. Fusarium culmorum, F. graminearum, F. avenaceum and F. poae) and non-toxin producing species (e.g. Microdochium nivale vars. majus and nivale). The chief toxins produced are trichothecenes, of which deoxynivalenol (DON) and nivalenol (NIV) are most commonly associated with FEB. 

Field trials were carried out over three years at each of three sites in the UK. Wheat plots were inoculated at mid-anthesis with a mixture of toxin producing and non-toxin producing species. Fungicides were applied 2-3 days post inoculation (years 1 and 2) or pre- or post inoculation (year 3) to determine their efficacy in controlling disease, each of the fungal species and toxin accumulation in the grain. Disease was assessed visually and grain was analysed to determine the relative amounts of each fungal species present and also the amount of DON toxin. 

Fungicides were differentially active against the toxin-producing and non toxin-producing species that cause FEB. Azoxystrobin had very high activity against M. nivale but only very limited activity against Fusarium species. In contrast, tebuconazole, metconazole and HGCA2 had high activity against the Fusarium species while being ineffective against M. nivale. The control of disease and toxin accumulation was generally related to fungicide dose for those compounds with activity against Fusarium species. Efficacy was reduced with reduced fungicide dose. Pre- and post inoculation fungicide application controlled disease to similar extents where application was very close to the time of inoculation (±2-3 days). Where Fusarium species predominated at a site, application of azoxystrobin generally did not markedly affect the level of disease or toxin accumulating in grain. However, where significant amounts of M. nivale were present, the application of azoxystrobin sometimes led to increases in the toxin content of grain. 

Although the reduction in the DON content of grain was sometimes very large relative to the untreated plots, in no case did fungicide application lead to a level of DON below 0.75 ppm (mg/kg). 

Lodging occurred on one site in the last year of the project. High levels of DON were detected in grain from the plots where lodging occurred, overwhelming the effect of fungicide application. 

The use of double fan nozzles combined with a reduced tractor speed greatly improved coverage of wheat ears with fungicide and led to improved control of disease.