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The Alberta Fusarium head blight risk forecast: A useful tool for FHB

By Jeremy Boychyn (M.Sc)(P.Ag), Agronomy Research Extension Specialist

Fusarium head blight (FHB) caused by Fusarium graminearum (Fg) is an increasing concern in Alberta (Harding et al., 2018). FHB leads to Fusarium damaged kernels (FDK) and deoxynivalenol (DON) causing impacts to crop yield, quality and grade. In some cases, it can render a crop unmarketable.

Complete eradication of Fg from a field is impossible once it is established. However, tactics can be implemented to mitigate its impact (See managefhb.ca for more details on management tools for FHB caused by Fg). One of those tactics is monitoring weather for conditions favouring FHB infection.

At flag leaf emergence timing, it is important to monitor for environmental conditions conducive to higher risk of FHB development. Being aware of high-risk conditions can assist decision-making regarding fungicide application.

Temperatures of 10-30°C along with adequate moisture allow Fusarium fungus to become active (Sutton 1982, Tschanz et al., 1976, Ye 1980). Once active, sporulating occurs producing fruiting structures known as perithecia. Perithecia then produce wind-dispersed spores known as ascospores which infect the exposed cereal head. Conditions conducive for infection are 48 hours of high humidity or rainfall and optimum temperatures are around 25°C (Sutton 1982, Parry et al., 1995).

Although the greatest risk of infection occurs during anthesis (flowering), infection can occur at any point between head emergence and crop senescence (personal communication with Dr. Kelly Turkington of Agricultura and Agri-food Canada, Lacombe). Infections that occur during anthesis are more likely to cause FDK, especially in wheat. Infections that occur after anthesis timing may not cause FDK, however they can lead to elevated levels of grain accumulated DON.

Fusarium overwinters in grain and crop residue in the field. Fields with a shorter rotation are at higher risk of infection. This is due to build-up of infected crop residues from FHB host crops and a lack of time to allow for decomposition of infected material.

Figure 1: Image of FHB on wheat head indicated by premature kernel ripening and salmon pink/orange material between infected florets. Image courtesy of Dr. Kelly Turkington Agriculture and Agri-Food Canada. 

Figure 2: Image of FHB on barley head indicated by brownish discolouration. Barley FHB can often be mistaken with spot blotch/kernel smudge infection or even hail damage. A key indicator with barley is pinkish/orange or whitish growth on affected head portions. Image courtesy of Dr. Kelly Turkington Agriculture and Agri-Food Canada.  

Monitoring local temperature, rainfall and humidity over an extended period to assess FHB risk can be challenging. However, the Fusarium Head Blight Risk Tool was developed to ease that challenge. The tool provides producers and agronomists a Fusarium Disease Severity Value by allowing them to select their closest weather station to assess FHB risk. It is available from June 1 – August 15 and can assist with FHB spray decisions. The risk value, which accounts for rainfall, humidity, and temperature over time, indicates infection risk for the region surrounding that weather station. The higher the risk value indicated, the higher risk of FHB infection.

Figure 3: Screenshot from the Fusarium Head Blight Risk Tool indicating FHB risk in Barrhead over the second half of June 2021.

Keep in mind, the information provided in the Fusarium Head Blight Risk Tool is only part of the decision-making process. It is important to ground-truth weather information. Walk fields and determine if moisture in the canopy is representative of the FHB risk tool. For example, if the soil surface and crop canopy are wet well into mid-afternoon, then conditions may be favourable for FHB infection. Additionally, consider field and farm history of FHB infection caused by Fg. Fields with little to no history of FHB caused by Fg are at lower risk of infection, even under high-risk environmental conditions, as the field Fg spore load may be low. Crop stage is also an important consideration when assessing risk. High FHB infection risk prior to heading or after crop senescence are less likely to impact risk of infection. This is due to the crop not being in the infection risk stage of growth. Conversely, high FHB infection risk while the head is emerged is more likely to lead to FHB infection, assuming Fg spores are present. Finally, variety susceptibility and potential crop value can also impact the decision to spray. Once all factors are taken into consideration, an informed decision on fungicide application can be made.

Recommendations:

Begin monitoring the FHB risk tool every few days once your crop reaches flag leaf staging. As you get closer to head emergence, monitor for risk daily. This will allow ample time to assess risk and plan for fungicide application if required.

References:

Harding, M.W., Howard, R.J., Feng, J., Laflamme, P., Turkington, T.K., Gräfenhan, T., and Daniels, G.C. (2018). Monitoring Fusarium graminearum in Alberta: looking back 20 years. Can J. Plant Pathol. 40: 141.

Parry, D.W., P. Jenkinson, and L. McLeod. 1995. Fusarium ear blight (scab) in small grain cereals – a review. Plant Pathol. 44: 207-238.

Sutton, J.C., W. Baliko, and H.S. Funnell. 1980. Relation of weather variables to incidence of zearalenone in corn in southern Ontario. Can. J. Plant Sci. 60: 149-155.

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

Tschanz, A.T., R.K. Horst, and P.E. Nelson. 1976. The effect of environment on sexual reproduction of Gibberella zeae. Mycologia 68: 327-340.

Ye, H.Z. 1980. On the biology of the perfect stage of Fusarium graminearum Schw. Acta Phytophylacica Sin. 7: 35-42.