Fungicide application timing on Fusarium head blight and mycotoxin accumulation in barley in Japan

Abstract

Fungicide application is one measure available to reduce the risk of Fusarium head blight (FHB) and mycotoxin contamination in barley. The stage at or near anthesis, or at full head emergence, is generally thought to be optimal for fungicide application, regardless of cultivar. However, we have found that the most critical time for Fusarium graminearum infection and mycotoxin accumulation in barley differed among cultivars. Whereas open-flowering cultivars were most susceptible at anthesis, closed-flowering cultivars were considerably resistant at anthesis but became susceptible after ‘spent’ anther extrusion. Therefore, we evaluated the effect of the timing of fungicide application on FHB and mycotoxin (deoxynivalenol and nivalenol) accumulation in closed-flowering barley. Thiophanate-methyl fungicide was applied at different developmental stages, from before anthesis to 30 days after anthesis (DAA), under artificial inoculation conditions in the field in which inoculum spores were provided throughout the testing period. As expected, the optimal timing for chemical control of FHB and mycotoxin accumulation was the time around the beginning of spent anther extrusion, rather than at anthesis. Later application, as late as 30 DAA, was also effective in controlling mycotoxin accumulation, although it was not effective in controlling disease levels. Our results suggest that the development of control strategies that cover the late stage as well as the early stage is desirable to reduce the risk of mycotoxin contamination in barley.