Fusarium Head Blight Biology
FHB is caused by fungal species in the genus Fusarium. The most common species causing FHB is Fusarium graminearum (sexual stage — Gibberella zeae). This fungus is the same one that frequently is associated with stalk rot of corn. Another Fusarium species that causes FHB is Fusarium culmorum. Both F. graminearum and F. culmorum also may cause root rot of small grains. On barley, two other Fusarium species, F. poae and F. avenaceum, also may cause kernel blight.
The fungus persist and multiply on infected crop residues of small grains and corn (see disease cycle, Figure 7). During moist weather, spores of the fungi are windblown or splashed onto the heads of cereal crops. Spores can come from within a crop or can be blown from surrounding crops sometimes long distances away. Wheat and durum crops are susceptible to infection from the flowering (pollination) period up to hard dough stage of kernel development. Spores of the causal fungus may land on the exposed anthers at flowering time and then grow into the kernels, glumes or other parts of the head. For spring barley, which flowers when the head is in the boot, infection is most common after the flowering period, once the head breaks through the leaf sheath. Infection in either crop may continue until close to grain maturity under favorable environmental conditions for the organism(s).
The most favorable conditions for infection are prolonged periods (48 to 72 hours) of high humidity and warm temperatures (75 to 85 degrees Fahrenheit (24°C to 30°C)). However, infection does occur at cooler temperatures when high humidity persists for longer than 72 hours. Early infections may produce air-borne spores, which are responsible for secondary spread of the disease, especially if the crop has uneven flowering due to late tillers.
Since FHB development depends on favorable environmental conditions from flowering (head emergence in barley) through kernel development, disease occurrence and severity varies from year to year. A combination of factors that may lead to the severest yield and quality losses are: abundant inoculum, prolonged or repeated periods of wetness and high humidity during flowering (head emergence in barley) through kernel development, and use of a very susceptible cultivar.