In a Fusarium head blight (FHB) epidemic, the combination of cultivar resistance and effective fungicide application is expected to provide maximum reduction of FHB and DON in winter barley. Especially for malting end-use, there is a very low tolerance for Fusarium infections in barley grain. However, the best timing for fungicide application to manage FHB in barley is not well understood. An experiment on fungicide efficacy and timing was conducted at Raleigh in a misted, inoculated nursery with 4 trials, one per year from 2016 to 2020. Three winter barley cultivars were utilized that had different levels of FHB resistance:  Violetta (MR), Thoroughbred (MR/MS), and Flavia (S). Violetta and Flavia were medium-late two-row malting cultivars, while Thoroughbred was a medium-maturing six-row feed type with acceptable malt quality.

Inoculation was provided via F. graminearum-infected corn spawn, and the experiment was mist-irrigated. Fungicides were Miravis Ace (adepidyn + pydiflumetofen), Prosaro (prothioconazole + tebuconazole), and, starting in the second year, Caramba (metconazole). The three timings for fungicide application were:  50% spike emergence (Feekes 10.3), 100% spike emergence (Feekes 10.5), and 100% emergence + 6 days. The experiment had a split-plot design with four replicate blocks in each year.

Over the four years, two of the epidemics had high intensity and two had low intensity. Combining the data across years, cultivars, and fungicides, the latest timing was significantly superior at reducing DON, followed by the intermediate timing (P < 0.05). The early timing was least effective in reducing DON and was not significantly different from the untreated control. In an assay of percent kernels infected with Fusarium, the results were the same:  across years, cultivars and fungicides, mean infected kernel percentages were significantly reduced by the late application, followed by the intermediate application, and the early application was not different from the untreated control (P < 0.05).  The three fungicides performed similarly at the early timing except that Miravis Ace reduced visible symptoms more than did Caramba (P < 0.05).

Taken together, these results indicate that the recommendation traditionally given for spring barley to apply an FHB-targeted fungicide at full spike emergence (Feekes 10.5) may not be best for winter barley. Waiting until 6 days after Feekes 10.5 to apply a fungicide appears preferable for reducing both DON and percentages of barley kernels infected with Fusarium.