Fusarium head blight (FHB) is a fungal disease that may infect a number of crops in Canada-wheat, barley, oats, rye, corn, canary seed and forage grasses. However, the crops most affected are wheat, barley and corn.

Fusarium head blight is not a new disease. It was identified over 100 years ago, in 1884, in England. It was first called wheat scab, and later, tombstone disease, because of the chalky, lifeless appearance of the infected kernels.

FHB has occurred in eastern Canada and the USA for many years. Losses from FHB in eastern Canada date to at least the early 1940's. Fusarium graminearum was first identified in Manitoba in 1923, but no serious outbreaks were reported until 1984. Since then, surveys in western Canada conducted by the Grain Research Laboratory have found F. graminearum in an ever-expanding area, now reaching into northern BC.

F. graminearum is only one of many species of Fusarium, but it is considered the most important one in Canada because of the impact it has on yield and grain quality, its ability to produce several different toxins, and its abundance in eastern Canada and the eastern prairies.

In eastern Canada, it appears to be well established in all the cereal growing areas. In western Canada, F. graminearum is found most frequently in the black soil zone. This zone is also the area of highest rainfall on the prairies. Infection is associated with rainfall during the flowering stage. The infection is spread by wind, but the pathogen is also spread by planting infected seed.

Average level of July precipitation on the prairies, 1961-1990

Fusarium head blight is most successful when rainfall occurs during the flowering stage, usually in July. This map shows the 30 year average precipitation for July in the crop districts of western Canada. Many areas of western Canada have precipitation levels in July equivalent to those of southern Manitoba, indicating that moisture levels at flowering will likely promote further westward spread of F. graminearum.

Average daily mean temperature in July

Temperature is considered a primary factor influencing species dominance in FHB. July temperatures in the western prairies are cooler than in the eastern prairies. F. avenaceum and F. culmorum are considered to be better suited to cooler conditions than F. graminearum. However, F. graminearum is the dominant FHB pathogen in the maritime provinces, where summer temperatures are cooler than on the prairies. Temperature may play a role in moderating FHB in the western prairies, although the extended daylight hours in summer in the more northern areas of the prairies may compensate somewhat for the lower daily mean temperature. One unknown is the impact of global warming on prairie temperatures and precipitation.

Seedling blight can occur when planting infected seeds

Fusarium head blight results in the production of visibly damaged seeds called fusarium-damaged kernels (FDK), as well as infected seeds which don't display visible symptoms of infection. These non-symptomatic seeds usually outnumber the FDK by a considerable margin. Planting infected seeds can result in a second disease called seedling blight.

Appearance of kernels with fusarium damage

Fusarium-damaged kernels (FDK) have also been called scabby, or tombstone. These names describe the appearance of wheat kernels affected by fusarium head blight. Such kernels are shriveled and chalky white.

Effects of fusarium head blight are greater the earlier it strikes

EarlyLate

The earlier in the life cycle of a kernel that fusarium head blight strikes, the greater its effect. In this picture, the kernels were infected at progressively later stages of development. The three kernels on the left show what fusarium-damaged kernels look like before harvest. Much of the white fuzzy coating is lost during harvest, as shown by the three kernels on the right. Although the two kernels on the far right may appear to be normal, they are slightly infected.

Symptoms of fusarium head blight on various grains

Rye
Wheat

Shriveled, chalky white, with fungal webbing in crease or germ

Barley
Oats

Orange and black encrustation on seed surface

Four species in North America can cause Fusarium head blight.

Three species in North America are routinely found to produce it.

Two of these produce DON (vomitoxin).

F. graminearum = Gibberella zeae

Conidiospores
Sporodochia

Conidiospores are formed in sporodochia.

Asci containing ascospores
Perithecia

Ascospores are formed in perithecia.

These pictures show two stages in the life cycle of F. graminearum. The imperfect stage is called Fusarium graminearum and the perfect stage is called Gibberella zeae. Both stages can occur together.

The distribution of F. graminearum and soil zones on the prairies

These maps show sites on the prairies where F. graminearum has been recovered from FDK based on seed surveys done at the Grain Research Laboratory between 1994 and 2002.

1994 1995 1996 1997 1998 1999 2000 2001 2002

F. graminearum is one of four species in Canada that cause fusarium head blight and is the most important. F. graminearum had been found mostly in black soil zones, which are also areas of highest precipitation.

Average level of FDK in CWRS

These maps show the average level of FDK in CWRS wheat samples collected at the Canadian Grain Commission. Most of the wheat samples from western Canada had little to no FDK. Areas with the highest levels are those where F. graminearum is the primary causal agent.

1995 1996 1997 1998 1999 2000 2001 2002

Relative frequency of species recovered from FDK on the prairie provinces from 1995 to 2002

These graphs illustrate the relative frequencies with which the main fungi isolated from FDK have been recovered from Alberta and Manitoba in 1995 to 2002, and from Saskatchewan in 1995 to 1997. Because of the considerable difference in crop district results developing in Saskatchewan by 1998, the results for that date and afterwards have been presented as separate crop districts (see Saskatchewan 1998 to 2002 results below). F. graminearum continues to be the species responsible for almost all the FDK in Manitoba. F. avenaceum was the primary species from Saskatchewan till 1997, when F. graminearum replaced it as the dominant species recovered from FDK. In Alberta, Septoria nodorum has traditionally been the species most often isolated from the few FDK found in wheat from that province (especially the northern areas). This fungus is the causal agent of glume blotch, and although it is not a species of Fusarium, it can produce a kernel visually indistinguishable from those produced by the Fusaria causing FHB. In Alberta, the few kernels infected by F. graminearum are usually found in the southern CDs, although not in 2000 or 2001 when a severe drought occurred. However, in 2002 unusually wet weather in southern Alberta resulted in a considerable increase in the number of wheat samples with FDK and the number of FDK within the affected samples. The great majority of samples with FDK were of the amber durum wheat class. F. graminearum and F. culmorum were common causes of the FDK in southern Alberta in 2002. Due to a drought in central and northern Alberta in 2002, very few FDK were collected from those areas. Other fungi were also found infecting FDK, and they varied in frequency from 3% to 31%. The most common of these fungi was Alternaria alternata. Other important members of this category were Apiospora montagnei, Asteromella spp., F. poae, F. sporotrichioides, and Nigrospora oryzae.

Percentage of species infecting FDK in Saskatchewan crop districts, 1998

This graph illustrates the difference in species infecting FDK in Saskatchewan in 1998 when tabulated by crop district. F. graminearum was dominant in south eastern Saskatchewan (CDs 1, 2, and 5) in 1998. Those CDs also had the highest percentage of wheat samples in Saskatchewan containing FDK (23.5%, 1.5% and 7% respectively). Although F. graminearum was also dominant in CDs 3/4 and 7, very few FDK were found in those areas.

Percentage of species infecting FDK in Saskatchewan crop districts, 1999

This graph illustrates the difference in species infecting FDK in Saskatchewan in 1999 when tabulated by crop district. As in 1998, F. graminearum was dominant in southeastern Saskatchewan (CDs 1, 2, and 5). CDs 1 and 5 had the highest percentage of samples with FDK, as well as the greatest number of FDK. F. graminearum was not the dominant species in any other Saskatchewan CD in 1999.

Percentage of species infecting FDK in Saskatchewan crop districts, 2000

This graph illustrates the difference in species infecting FDK in Saskatchewan in 2000. The relative distribution of the causal species is very similar to that of 1999. However, in 2000 F. graminearum was not dominant in CD 2, but it was in CD 8. CDs 1 and 5 continued to have the highest percentage of samples with FDK as well as the highest levels of FDK in Saskatchewan.

Percentage of species infecting FDK in Saskatchewan crop districts, 2001

This graph illustrates the difference in species infecting FDK in Saskatchewan in 2001. The relative distribution of the causal species is very similar to that of recent years. F. graminearum was the primary FHB pathogen in CDs 1, 2, and 5. The percentage of wheat samples with FDK in those CDs was 58%, 14%, and 12% respectively, a considerable rise over past years. Although it was present in other CDs, there were very few samples of wheat with FDK from outside the south-eastern corner of the province.

Percentage of species infecting FDK in Saskatchewan crop districts, 2002

This graph illustrates the difference in species infecting FDK in Saskatchewan in 2002. F. graminearum was the primary FHB pathogen in CDs 1 and 5, whereas F. avenaceum was the dominant species in most other Saskatchewan crop districts. Unusually wet weather in normally dry areas of Saskatchewan resulted in a considerable rise in the number of samples with FDK (especially CDs 3/4 and 6), the majority of which were infected by F. avenaceum and S. nodorum.

Percentage of wheat samples containing FDK

This graph shows the percentage of wheat samples containing FDK in the 3 prairie provinces, 1996 to 2002. It is based on the results of the CGC's harvest surveys. The percentage of wheat samples affected was higher in 2002 than any previous year, but the average level of FDK in the eastern prairies was down from 2001. FHB remains a minor disease in Alberta and most of Saskatchewan.

References

Abramson, D., R.M. Clear and T.W. Nowicki. 1987. Fusarium species and trichothecene mycotoxins in suspect samples of 1985 Manitoba wheat. Can. J. Plant Sci. 67: 611-619.

Bisby and Bailey. 1923. Ear and root rots. Page 33 In Fourth Annual Report of the Survey of the prevalence of plant diseases in the Dominion of Canada. Ottawa, Ont.

Clear, R.M. and D. Abramson. 1986. Occurrence of fusarium head blight and deoxynivalenol (vomitoxin) in two samples of Manitoba wheat in 1984. Can. Plant Dis. Surv. 66(1): 9-11.

Clear, R.M. and S.K. Patrick. 1990. Fusarium species isolated from wheat samples containing tombstone (scab) kernels from Ontario, Manitoba, and Saskatchewan. Can. J. Plant Sci. 70: 1057-1069.

Clear, R.M. and S.K. Patrick. 1993. Prevalence of some seedborne fungi on soft white winter wheat seed from Ontario, Canada. Can. Plant Dis. Surv. 73(2): 143-149.

Clear, R.M., S.K. Patrick, R.G. Platford, and M. Desjardins. 1996. Occurrence and distribution of Fusarium species in barley and oat seed from Manitoba in 1993 and 1994. Can. J. of Plant Pathol. 18:409-414.

Clear R.M. and S.K. Patrick. 2000. Fusarium head blight pathogens isolated from fusarium damaged kernels of wheat in western Canada, 1993 to 1998. Can. J. Plant Pathol. 22(1): 51-60.

Clear, R.M., S.K. Patrick, and D.Gaba. 2000. Prevalence of fungi and fusariotoxins on barley seed from western Canada, 1995 to 1997. Can. J. Plant Pathol. 22(1): 44-50.

Clear, R.M., S.K. Patrick, and D.Gaba. 2000. Prevalence of fungi and fusariotoxins on oat seed from western Canada, 1995 to 1997. Can. J. Plant Pathol. 22: 310-314.

Duthie, J.A., R. Hall and A.V. Asselin. 1986. Fusarium species from seed of winter wheat in eastern Canada. Can. J. Plant Pathol. 8: 282-288.

Gilbert, J. and A. Tekauz. 2000. Review: Recent developments in research on fusarium head blight of wheat in Canada. Can. J. Plant Pathol. 22(1): 1-8.

Gordon, W.L. 1933. Species of Fusarium isolated from field crops in Manitoba. Vol. 2, Proceedings of the World's Grain Exhibition and Conference, Canada.

Gordon, W.L. 1944. The occurrence of Fusarium species in Canada. I. Species of Fusarium isolated from farm samples of cereal seed in Manitoba. Canadian J. of Research 22: 282-286.

Gordon, W.L. 1952. The occurrence of Fusarium species in Canada. II. Prevalence and taxonomy of Fusarium species in cereal seed. Can. J. Bot. 30: 209-251.

Gordon, W.L. 1954. The occurrence of Fusarium species in Canada. IV. Taxonomy and prevalence of Fusarium species in the soil of cereal plots. Can. J. Bot. 32: 622-629.

Gordon, W.L. 1956. The occurrence of Fusarium species in Canada. V. Taxonomy and geographic distribution of Fusarium species in soil. Can. J. Bot. 34: 833-846.

Gordon, W.L., J.E. Machacek and W.A.F. Hagborg. 1948. Diseases of cereal crops. Wheat. Head Blight. Can. Plant Dis. Surv. 28: 1.

Greaney, F.J. and J.E. Machacek. 1942. Prevalence of seedborne fungi on cereals in certain seed inspection districts of Canada. Sci. Agric. 22: 419-437.

Machacek, J.E., W.J. Cherewick, H.W. Mead, and W.C. Broadfoot. 1951. A study of some seed-borne diseases of cereals in Canada. II. Kinds of fungi and prevalence of disease in cereal seed. Sci. Agric. 31: 193-206.

MacInnes, J. and R. Fogelman. 1923. Wheat scab in Minnesota. U. of Minn. Agric. Exp. Sta. Tech. Bull. 18, 32 pp.

Sutton, J.C. 1982. Epidemiology of wheat head blight and maize ear rot caused by Fusarium graminearum. Can. J. Plant Pathol. 4: 195-209.

Tekauz, A., B. McCallum, and J. Gilbert. 2000. Review: Fusarium head blight of barley in western Canada. Can. J. Plant Pathol. 22(1): 9-16.

Tervet, I.W. 1945. The microflora of wheat and barley seed grown in Minnesota and the Dakotas in 1944. The Plant Disease Reporter 29(19): 474-487.