The effect of different timings of fungicide applications on Fusarium head blight severity and mycotoxin accumulation in wheat grain was investigated in two field experiments. The fungicides metconazole, tebuconazole, azoxystrobin and mixtures of metconazole + azoxystrobin and tebuconazole + azoxystrobin were applied either, 5 days pre-, 2 days pre-, 2 days post-or 5 days post-inoculation of wheat ears with
spp. at GS 65. Fungicides applied 2 days pre-or 2 days post-inoculation were most effective at reducing Fusarium head blight severity and DON concentration in grain. Metconazole and tebuconazole applied alone within two days of inoculation were most consistent in their effects on
DNA and DON in harvested grain.
Saprophytic microflora and non-toxin producing Microdochium spp. capable of causing Fusarium head blight (FHB) have been suggested to affect the development of FHB caused by Fusarium spp., the occurrence of mycotoxins and the efficacy of fungicides for the control of the disease. The effects of metconazole and azoxystrobin on the interactions between Fusarium culmorum and Microdochium spp., Alternaria tenuissima or Cladosporium herbarum on FHB symptom development, Tri5 DNA concentration and deoxynivalenol (DON) production were studied under glasshouse conditions. Results indicated that the sequence of infection of wheat heads and the relative timing of fungicide application can significantly affect FHB severity and the resulting mycotoxin contamination of harvested grain. Introduction of A. tenuissima, C. herbarum or Microdochium spp. to wheat heads at GS 57 before inoculation with F. culmorum at GS 65 generally resulted in increased FHB severity, Tri5 DNA and DON concentration in harvested grain. The greatest increases of FHB severity (266%), Tri5 DNA (79%) and DON (152%) were observed when Microdochium spp. were introduced first at GS 57 and F. culmorum inoculation followed at GS 65. Metconazole generally reduced FHB severity, Tri5 DNA and DON concentration in grain but azoxystrobin was most efficient at reducing DNA of Microdochium spp. in grain.