Assessments of fusarium head blight of wheat and barley in response to fungicide treatment

Benomyl and tebuconazole reduced head blight incidence, head blight severity, and the percentage of visually scabby kernels (VSK) in harvested grain when applied to the susceptible spring wheat cv. Norm at anthesis. Deoxynivalenol (DON) concentration was also reduced. Fungicide treatment increased head weight, test weight, thousand kernel weight, and yield. Fludioxonil reduced certain parameters associated with the disease in barley, including incidence, severity, and deoxynivalenol concentration, while increasing the percentage of plump kernels and yield. In vitro, isolates of Fusarium graminearum were sensitive to fludioxonil, benomyl, tebuconazole, and mancozeb (concentrations that give 50% growth inhibition of 7.4 x 10(-3), 3.5 x 10(-1), 9.9 x 10(-1), and 7.3 mg a.i./liter, respectively). No evidence for insensitivity (resistance) was found. Prospects for chemical control of Fusarium head blight (FHB), however, remain limited. The repeatability of assessment methods used in evaluating host response to fungicides and to the damage caused by F. graminearum is discussed. Disease incidence, disease severity, VSK, and DON were identified as key variables that best measure the effects of FHB.