Wheat Diseases
Fusarium head blight (FHB), or scab, is a fungal disease that can occur on all small-grain crops, but is seen most commonly on spring and winter wheat, durum, and barley. FHB is caused by fungal species in the genus Fusarim, with the most common species being Fusarium graminearum. FHB can cause significant yield losses and quality reduction. Yield losses in all crops occur from floret sterility, additional yield and quality losses can occur from shriveled and light test-weight kernels. Quality reductions also may occur if fungal toxins (mycotoxins) are produced in infected seeds.
DISEASE SYMPTOMS
In wheat, FHB symptoms may appear as part or all of the head being bleached. The fungus may also infect the stem (peduncle) immediately below the head, causing a brown/purple discoloration of the stem tissue. Additionally, during prolonged periods of wet weather signs of FHB infection can be seen as pink to salmon-orange spore masses of the fungus on the infected spikelets and glumes.
Many infected wheat kernels are shriveled, lightweight and a dull gray or pink. If infection occurs late in kernel development, infected kernels may be normal in size, but have a dull appearance or a link discoloration.
FAVORABLE ENVIRONMENTAL CONDITIONS
The most favorable conditions for FHB infection are long periods (48 to 72 hours) of high humidity and warm temperatures (75 to 85ºF). 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. Combined, the most severe yield and quality losses are seen when abundant inoculum is present, prolonged or repeated periods of wetness and high humidity during flowering through kernel development, and the use of susceptible cultivars.
DISEASE MANAGEMENT
While no commercial cultivar is completely resistant to FBH, two types of resistance (Type 1 and Type 2) have been shown to resist kernel infection, degrade mycotoxins, and maintain yield despite the presence of FHB. The use of seed treatment can help reduce seedling blight due to infected seed but will not protect against subsequent head blight.
Tillage practices that bury residue from small grains and corn reduce the inoculum potential of the fungus. In minimum or no till practices, effective spreading and distribution of chaff and other residue may reduce inoculum potential. Crop rotation to a non-host crop or planting of a small grain on last year's broad-leafed crop is effective in reducing FHB.
Staggering planting date of small-grain crops or planting cultivars of differing days to maturing can reduce the risk of the entire crop flowering or going through early grain fill during a period favorable for FHB infection. A fungicide spray program consisting of Triazole fungicides may help reduce FHB disease damage. At harvest, the combine can be adjusted to remove the light-weight FBH kernels along with the chaff. However, it is important to note that not all FHB kernels will be removed during this process.