Fusarium Head Blight (FHB), also known as scab, is a fungal disease of small cereal grains including wheat, corn, barley, rye, oats, triticale, canary seed and some forage grasses.
Favourable Conditions for FHB
The disease overwinters in the soil as spores or as mycelium on crop residue and root crowns and can also survive in the grain. Development of FHB is favoured by humid conditions, infecting crops from flowering through to the soft dough stage. However, the most damaging level of infection occurs during the flowering stage.
Symptoms
Infected wheat spikelets will bleach prematurely. As well, FHB will produce orange, spore-bearing structures called sporodochia at the base of the glumes. During a wet season, there may be whitish, occasionally pinkish, fluffy fungal growth on infected heads. Kernels from infected wheat spikelets are shrunken and usually white. In barley, it's called fusarium mould and will cause an orange or black crust over the seed surface.
Effects
Crops infected with fusarium will have reduced yields, the affected kernels have lowered levels of protein and weight, and bread- and pasta-making quality is greatly reduced. The Canadian Grain Commission sets maximum tolerated levels of fusarium-damaged kernels (FDK) for various grades of wheat.
Example: Canadian Western Red Spring Wheat
| Grade name | Fusarium damage % by weight |
| No. 1 CWRS | 0.25 |
| No. 2 CWRS | 0.8 |
| No. 3 CWRS | 1.5 |
| CW Feed | 4.0 |
Fusarium-infected kernels are often lighter in weight than non-infected kernels. Conventional cleaning methods can often reduce the amount of infected kernels in the sample.
For livestock, the concern is not necessarily about Fusarium; the issue is with the mycotoxins that Fusarium species can produce. The disease may produce a number of mycotoxins, including zearalenones and trichothecenes. Each group of mycotoxins are comprised of several metabolites that are tested for separately. For example, trichothecenes are comprised of 7 metabolites, including deoxynivalenol (DON or vomitoxin), diacetoxyscirpenol (DAS), T-2 toxin and HT-2 toxin. Mycotoxins are found in the infected grain and its chaff; little, if any, is found in the straw and leaves of the plant. DON and other mycotoxins can also be found in cereal greenfeed and silage if those crops were infected by fusarium. Animals consuming feed containing high levels of mycotoxins may have a reduced immune response, reduced feed consumption, refuse feed all together as well as reduced fertility and in worst cases, the toxins can lead to death of the animal.
Agriculture and Agri-Food Canada (AAFC) has regulatory guidelines for maximum tolerated levels of mycotoxins in livestock diets. Note that stress as well as the presence of other mycotoxins can influence an animal's response. Please contact your local Regional Livestock Specialist to determine which mycotoxins you should be testing for as well as the maximum recommended levels for your animals.
Levels indicated by AAFC are based on a complete ration, using a dry matter basis If a mature beef cow was fed 5 pounds of grain that contained 20 ppm DON and 30 lbs. of hay and other forage, the cow would be consuming a total of 2.8 ppm DON (total diet) which is below the regulatory guidelines.
If fusarium-contaminated grain is going to be fed to livestock, it is advisable to have it tested for the presence of mycotoxins at the Prairie Diagnostic Services laboratory.