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Background
Fusarium head blight (FHB) is a fungal disease of cereal crops that affects kernel development. The most important cause of FHB is the fungus Fusarium graminearum, which causes significant losses in grain yield and grain quality, while also resulting in the production of mycotoxins that affect livestock feed, the baking and milling quality of wheat and the malting and brewing qualities of malt barley. The Canadian Grain Commission allows very little FHB (expressed as fusarium damaged kernels, i.e. FDK’s) tolerances in top grades. FHB-infected seed often reduces levels of germination and seedling vigour. For more information, see:
Fusarium Damaged Kernels
Official Grain Grading Guide
FHB in Western Canada Overview
What is the host range of FHB?
FHB has a wide host range that includes all small grain cereal crops (wheat, barley, oat, rye, triticale), corn and many wild and tame grass species.
What is the life cycle of the FHB pathogen?
The pathogen causing FHB overwinters in crop debris/residues of small grain cereals and corn located on or in the soil. The pathogen also overwinters in infected seed. Seedlings can become infected at emergence. Warm, moist weather promotes spore germination on the infected crop residue that spread by wind to infect florets at the flowering stage of the cereal crop. A second, rain-splashed, spore stage can form on infected head tissue. Additional precipitation associated with air temperatures above 25 degrees C accelerates disease development.
What are the symptoms of FHB?
Visible symptoms appear about three weeks after floret infection. The common symptom is premature bleaching or blighting of heads. Partially blighted heads are most common. Florets may have a pinkish or orange-ish appearance near their base or just beneath the glumes. The seeds in blighted heads do not fill properly and appear shriveled and bleached. See photos:
FHB Symptoms (1), FHB Symptoms (2), Fusarium Damaged Kernels,
How does FHB spread?
Fusarium graminearum produces two different fungal spore types, one that spreads via wind and another that spreads via splashing water droplets from rain or irrigation. Short distance spread occurs via the dispersal of fungal spores that are blown by the wind from one cereal field to the next or from plant to plant via water splashing. Long distance spread occurs through the transportation of infected crop residue or seed.
What is the effect of FHB mycotoxins on livestock feed?
FHB produces a mycotoxin called deoxynivalenol (DON), a poisonous compound that accumulates in the head (grain and chaff) of cereal crops. Little, if any, DON is present in the straw and leaves of the plant. Although different livestock species react differently to this mycotoxin, animals consuming high levels of DON may experience reduced feed intake, reduced immune response and reproductive dysfunction. FHB-contaminated grain intended for livestock feed should be tested at a feed testing lab. Maximum tolerated levels of DON in livestock feed are 1 PPM for swine, dairy cattle and horses, and 5 PPM for beef cattle, sheep and poultry. See additional information at this Manitoba web-page, Feeding Fusarium Contaminated Grain to Livestock.
What is the FHB situation in Alberta?
FHB can be caused by several species of a fungal pathogen, Fusarium. The most important Fusarium species affecting Alberta is Fusarium graminearum. Results regarding the occurrence of F. graminearum, based on testing by a range of private and public organizations using different methodologies and involving a range of plant tissues (e.g. seed, heads, crowns, and nodes), have been consistent. Until the last few years F. graminearum was either not or infrequently isolated from grain, seed and crop residues from central to northern Alberta. In contrast, F. graminearum was more frequently isolated from grain, seed, cereal residues, corn residues, and head tissues from fields in southern Alberta, especially under irrigated production. Moreover, over the period from 2001 to 2013 this pathogen was being isolated with increasing frequency, especially in southern Alberta. Outside of southern Alberta during this period other less damaging species of Fusarium were typically associated with FHB symptoms. However, since 2013, F. graminearum is being more frequently detected in regions of Alberta outside of southern Alberta. For example, the number of counties in Alberta reporting F. graminearum in 2001 was 9, but the number jumped to 13, 22 and 26 in 2010, 2015 and 2016 respectively. F. graminearum is listed as a designated pest in the Agricultural Pests Act. A laboratory certificate showing that the seed lot in question was tested and found to be non-detectable for F. graminearum must accompany all cereal and corn intended for use as seed in Alberta. See Alberta Agriculture and Forestry’s Fusarium graminearum Management Plan
What can be done to reduce the risk of FHB on my farm?
Use a combination of agronomic strategies to manage FHB, including the following:
- Crop rotation: To reduce the buildup of infested crop residues, rotating away from cereals to non-host crops, including canola, pulses and forage legumes, should be considered for at least two years. This will allow enough time for infested residue to decompose before the next cereal crop is planted.
- Variety Selection: Although no cereal varieties are resistant, using the least susceptible varieties will help to reduce the risk of FHB and perhaps the potential for buildup of F. graminearum. For more information on FHB reactions of registered cereal varieties see the Varieties of Cereal and Oilseed Crops for Alberta document.
- Use Clean Seed: Producers must avoid planting seed that is infected with F. graminearum. Seed of susceptible crop species must be tested by a seed testing laboratory and only seed with non-detectable levels of F. graminearum is to be used for seeding purposes.
Although infected seed can cause seedling blight, it typically does not directly give rise to head blight symptoms in one growing season. The fungus will move from the infected seed to the root, crown and stem base tissues of the plant that develops from the infested seed, thus creating potential sources of infested residue that can impact subsequent crops. Buildup of the pathogen would typically be favoured by the production of successive host crops grown continuously or in short rotations, and disease-conducive weather.
- Seed Treatment: Although unable to prevent infection later in the growing season, seed treatment helps prevent seedling blights caused by FHB and other seed and soil-borne pathogens. Therefore, prior to planting a cereal crop, treat the seed with a registered fungicide that includes FHB on the label list of diseases that are controlled.
- Increase Seeding Rate: Increasing seeding rate causes less tillering leading to a more uniform and shorter overall flowering period which minimizes the length of time during which heads are susceptible to Fusarium infection. Less tillering means less variation in crop growth stage, which may improve fungicide performance. Less tillering and a shorter flowering period also reduces the time that irrigation should be avoided.
- Stagger Planting Dates: Humid weather during flowering in wheat or heading in barley favours Fusarium infection. Vary seeding dates to avoid having all cereal fields flowering at the same time.
- Fungicide Application: In-crop fungicide application may be considered, but only provides disease suppression. Disease symptoms form later in the growing season and are not visible at spraying time. See the Crop Protection guide (Blue Book) for registered fungicides. Strobilurin fungicides (group 11) should not be used with FHB management because they may cause increased DON contamination in harvested grain.
The period of time that a cereal plant is susceptible to infection is short. Therefore, the spray window is also short (approximately seven days). Warmer weather conditions narrow the spray window while cooler conditions widen the spray window. FHB fungal spores infect the cereal plant by entering openings created where tiny flowers, referred to as anthers, form on the cereal head. Wheat flowers after the head is fully emerged from the boot while barley begins flowering as the head emerges from the boot. Tiny yellow anthers initially form in the middle of a head, ultimately developing over the full length of the head and finally turning from yellow to white as they age and dry out before blowing away. A field is considered to be at full flower when 50% of the heads on main stems are flowering.
Under ideal growing conditions, the length of time from when the wheat head is just emerging from the boot to the beginning of flowering is three days, so begin scouting closely when the head begins to emerge from the boot. The spray window begins when most of the heads on the main stems are fully emerged from the boot and continues through the time when yellow anthers form on the heads until 50% of the heads on main stems are in flower. As mentioned, barley begins to flower in the boot, however, wait until most of the barley heads have emerged from the boot before spraying. Ultimately, good head coverage prior to infection is critical for improving fungicide efficacy for both wheat and barley.
- Post-harvest Management: Thorough chopping, uniform spreading and incorporation of infected cereal straw will encourage decomposition and reduce pathogen survival.
- Hay and Straw Management: Caution should be used when spreading bedding straw for livestock, especially straw imported from outside of the province, which could put the FHB pathogen in contact with the soil and potentially leading to further disease spread.
Further FHB Information
Further information regarding fusarium head blight can be obtained through your local extension representative or at a number of internet sites including:
Alberta Fusarium Graminearum Management Plan
Fusarium Head Blight of Barley and Wheat
FHB and Irrigation Management - Frequently Asked Questions
Varieties of Cereal and Oilseed Crops for Alberta
Crop Protection guide - "Blue Book"
FHB Management Video
Canadian Grain Commission
Fusarium Head Blight in Western Canada
FHB Maps and Charts
Manitoba Agriculture, Food and Rural Initiatives
Dealing with Fusarium Head Blight
Saskatchewan Agriculture and Food
Fusarium Head Blight
Prepared by Ag-Info Centre, 310-3276, Alberta Agriculture & Forestry
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