The incidence of fusarium head blight, incited by Fusarium graminearum and other Fusarium species, has been increasing in Manitoba since 1984. Surveys of farm fields were conducted from 1988 to 1991 to assess the prevalence, distribution, and severity of the disease in wheat in Manitoba. Results of the surveys showed that fusarium head blight occurs throughout Manitoba. South-central Manitoba had the highest percentage of infested fields and the highest number of severely affected fields. Hard red spring wheat had severity levels (trace to 40%) similar to those for semi-dwarf common and durum wheats. F. graminearum was the most prevalent species associated with head blight. F. culmorum and F. graminearum were more pathogenic than F. acuminatum, F. avenaceum, F. equiseti, F. poae, and F. sporotrichioides. A field inoculation experiment was conducted to determine the effect of F. graminearum on grain yield, seed quality, and related characters in a susceptible durum wheat cultivar. Averaged over two years, F. graminearum reduced grain yield, 1000-kernel weight, and kernel weight per spike by 32, 34, and 36%, respectively, at 28% severity of fusarium head blight. However, kernel number was not affected. F. graminearum also affected seed quality. Seed infection reduced germination in 1989 and plant emergence and grain yield in 1990. Infected seed was not an important source of inoculum of F. graminearum. The results indicate that fusarium head blight may pose a serious threat in years when conditions are optimal for disease development.
