Fusarium Head Blight of Barley and Wheat lays out the following strategies to limit the introduction, escalation and spread of fusarium head blight in Alberta:
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 2 years. This will allow enough time for infested residue to decompose before the next cereal crop is planted.
Although few cereal varieties are resistant, using the least susceptible varieties will help to reduce the risk of fusarium head blight (FHB) and perhaps the potential for buildup of F. graminearum. Producers in areas of higher risk should select varieties that exhibit some level of FHB resistance. In general, the level of FHB susceptibility decreases from durum wheat to CPS wheat to hard red spring wheat to barley and to oat. Winter wheat often escapes FHB infection because it flowers before Fusarium spores are present. While oat is the least susceptible, due to often being used for human food processing, there is a very low FDK tolerance. For more information on FHB reactions of registered cereal varieties see: Varieties of Cereal and Oilseed Crops for Alberta.
Use clean seed
Where possible, 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, therefore, creating potential sources of infested residue that can impact subsequent crops. Buildup of the pathogen would also be favoured by growing successive host crops continuously or in short rotations, and disease-conducive weather.
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 FHB infection. Less tillering means less variation in crop growth stage, which may improve overall fungicide performance. Less tillering and a shorter flowering period also reduces the time that irrigation should be avoided (during the flowering period) when the pathogen infects wheat and barley crops.
Stagger planting dates between fields
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.
If possible, limit irrigation just prior to and during the flowering period to reduce humid conditions in the crop canopy which would otherwise favour FHB infection. For further information on using irrigation management to minimize FHB, see Fusarium head blight – Irrigation management.
Growing season spray window
In-crop fungicide application may be considered, but can be inconsistent and only provides FHB disease suppression. Disease symptoms form later in the growing season and are not visible at spraying time. See the Alberta Blue Book (Crop Protection guide) for registered fungicides. Strobilurin fungicides (group 11) should not be used for FHB management because they may cause increased DON contamination in harvested grain.
The period of time that a cereal plant is susceptible to FHB infection is short. Therefore, the spray window is also short (approximately 7 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 flower parts, 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. For fungicide application purposes, 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 3 days, so begin scouting closely when the head begins to emerge from the boot.
The spray window begins when most of the wheat 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.
Barley begins to flower in the boot, however, so 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, thus waiting until all heads are out of the boot may be advisable.
Figure 1. Full head emergence and flowering stages of wheat. (Diagram adapted from Saskatchewan Ministry of Agriculture)
FHB risk forecast maps
Weather-based FHB risk forecast maps are currently being developed by Alberta Agriculture and Forestry to assist growers with making a spraying decision and for more accurate timing of a fungicide application.
This forecasting tool provides local and hourly FHB risk levels using near-real-time weather data that growers can correspond with the correct heading stage for appropriate fungicide application timing: ACIS Fusarium Head Blight Infection Risk Report.
This tool can be used to evaluate the real-time environmental risk of FHB, at any location in the province, as the crop begins to head and flower. Knowing the risk of temperature and rainfall to drive infection and disease development may be useful in making fungicide application decisions.
Dr. Tom Wolf of AgriMetrix Research and Training provides these fungicide spray recommendations for FHB:
- angle nozzles forward or use a double nozzle (forward and back)
- greater angles are better
- use coarse sprays
- maintain low boom height
- fast travel speeds are fine for vertical targets (cereal heads)
- water: recommend 15+ gallons per acre (70+ litres per acre)
Scout for symptoms
Search for premature bleaching of one or more wheat spikelets (Figures 1 and 3) at the late milk to early dough stage. For spring seeded cereals, this typically occurs during the last part of July or early August. Once symptoms are present it is too late to apply a fungicide, however, keeping a record of this information is valuable for your FHB disease management plan in subsequent growing seasons.
Symptoms in barley are much less distinct than wheat (Figure 4). Send suspicious looking cereal head samples to a laboratory to determine whether affected heads contain FHB infection and to determine whether the Fusarium species is F. graminearum or one of the less damaging FHB species, or possibly another disease that resembles Fusarium symptoms. Symptoms may also appear in threshed grain as FDK or discolouration, which should also be sent to a lab to determine Fusarium species. See laboratory suggestions in the next section.
Harvest management (combine adjustment)
Adjust fans to blow out lightweight infected wheat kernels, which may not be an option for infected barley and oat kernels that are not typically shrunken or shrivelled. While a majority of wheat kernels are lightweight, wheat kernels infected well after flowering and up to the soft dough stage of kernel development may be too heavy to blow out.
While there is some risk of having more wheat heads and straw pieces in the grain sample, some growers adjust the sieves to a more wide-open setting. A wider sieve setting slows the rearward flow of the grain mass that aids cleaning and separation of lightweight kernels due to a more vertically directed air blast. Thoroughly clean equipment used to harvest infected fields before moving to clean fields.
Harvest travel speed
Slower combine ground speed results in less material on the cleaning sieve and allows more time for the increased air blast to separate good kernels from lightweight, infected wheat kernels.
Consider harvesting early
Under moist weather conditions, FHB fungal growth and DON production continue to develop and spread in grain over 19% moisture content. Therefore, if inclement weather is forecasted, consider harvesting early, however, be aware that higher moisture grain is heavier, which reduces the effectiveness of blowing out lightweight wheat kernels.
Thorough chopping and uniform spreading of infected cereal straw will encourage decomposition and reduce pathogen survival. Research conducted over the last 20-30 years has found the impact of tillage to be variable, especially the typical forms of conventional tillage practiced in Alberta. Although moldboard ploughing may help, it is detrimental to soil health and increases the risk of erosion. Moreover, FHB is still an issue in areas that utilize moldboard ploughing.
Storage aeration and drying
Infected wheat should be aerated soon after storage to reduce grain temperature and fans should be turned on periodically thereafter as air temperatures decrease until the infected wheat is 5°C. If necessary, dry infected grain to 14% moisture content or lower. Drying temperatures should not exceed 60°C to retain milling quality.
Bin more infected grain separately if FHB levels vary between fields or within a field.
Gravity table and colour sorter
Although not entirely effective, gravity tables and optical colour sorters are able to separate out severely infected FDK to facilitate a grade increase. Although a gravity table is lower-cost, some FDK are missed while some healthy kernels are eliminated. FDK colour varies from white to pink to black, which can complicate and slow a colour sorting process. A practice of using a gravity table first to clean the grain followed by colour sorting is being applied, however, time and cost of grain cleaning increases.
Both colour sorters and near infrared technology (NIT), that determines the presence of chemical characteristics (DON) via light response, have considerable potential to increase the quality of a grain sample with Fusarium infection. These technologies will likely become more common as these technologies become more advanced, familiar and cheaper.
Control volunteer cereals and grassy weeds on infested land, including headlands.
Handling feed grain and grain spillage
Feed grain represents a risk for introducing F. graminearum due to the sheer volume of feed grain brought into Alberta. It is known that F. graminearum on infected grain is killed during passage through the digestive system of cattle. Feed grain must be handled responsibly to ensure that all infected grain is fed to cattle. Grain spillage should be avoided. Infected spilled grain should be cleaned up and composted, reaching a temperature of 60 degrees C for at least 2 weeks, which kills F. graminearum.
Careful feed grain loading/unloading
Infected grain must not be allowed to come in contact with the soil, which would allow F. graminearum to establish a foothold in roadsides or fields. Unloading sites must be covered or equipped with drop socks and wind fences to ensure that infected grain does not blow onto nearby soil. Trucks, or any vehicles, used to haul feed grain must be securely tarped. Trucks must be cleaned thoroughly at the unloading site and all remaining grain composted.
Feed grain storage
Limit the storage of feed grain/grain products in uncovered piles or in direct contact with the soil. Moisture contacting this grain can promote the growth and development of F. graminearum. Sites where infected grain/grain products were stored should be properly cleaned up and leftover grain composted.
Hay and straw management
Grass hay and straw from areas infested with F. graminearm can carry the pathogen and should be handled in accordance with the best management practices applied for feed grain. Grass hay represents a lower risk than straw because hay should all go through the cattle, which kills F. graminearum. Caution should be used when spreading infested livestock bedding straw in fields, which puts the FHB pathogen in contact with the soil. If the bedding straw is not collected and composted in early spring, any F. graminearum present may become established in the field or field edges.