By Sara Tetland, MSc, PAg, Provincial Specialist, Cereal Crops, Regina
June 2022
With many parts of the province receiving high amounts of moisture this spring and recent warm temperatures, you might be thinking about assessing your Fusarium Head Blight (FHB) risk and potentially spraying for suppression.
FHB is a mono-cyclic disease, so once you can see symptoms the plant is already infected and it is too late to treat with fungicides. Therefore, the decision to spray must be made before detection of the disease is possible. This can be done by assessing the risk of FHB infection and then deciding whether to spray based on that risk level.
For disease infection to occur, all three sides of the disease triangle must be present, which are:
- Presence of a susceptible host;
- Presence of a virulent pathogen; and,
- Presence of suitable environmental conditions.
Presence of susceptible host: Cereal crops and many grass species are susceptible to FHB infection. Oat and barley are more resistant to FHB than wheat or durum. There are varying levels of resistance between wheat and durum varieties. Many of the spring wheat varieties are rated with intermediate or moderately resistance and many of the durum varieties are susceptible or moderately susceptible. Improvements in resistance have continued over the years and breeders continue to focus on breeding for FHB resistance. Ratings of specific varieties can be found in the 2022 Varieties of Grain Crops.
Infection of wheat heads can occur up to the soft dough stage, but they are most susceptible during flowering (anthesis). Risk assessment and potential application of fungicides must be made before this point.
Presence of virulent pathogen: Fusarium spp., the causal agent of FHB, is present throughout Saskatchewan and FHB occurs across the province, particularly in wet years. Crop rotation, with a one, preferably two-year break between cereals allows time for infected crop residue to break down and reduces the amount of pathogen present. Field specific risk can be assessed based on past infection and management practices.
Presence of suitable environmental conditions: Weather is the greatest factor in development of FHB. This means, when assessing risk, it is important to watch the weather and understand when it might increase risk of FHB infection.
FHB favours warm and high humidity conditions. Disease is most likely to occur when plants are flowering and when temperatures are between 15 to 30 C, with the optimum range for Fusarium graminearum being around 25 C. For Fusarium spores to germinate and infect, high humidity or precipitation is required for at least 12 hours. Spores can spread by wind or rain-splash, which causes residue to move from the soil surface to the head of the plant.
SaskWheat produces FHB risk maps which provide insight on the risk in your general area. These maps are based on weather conditions that contribute to FHB. When using these maps, it is important to accurately stage the crop and monitor the maps as the crop is nearing the susceptible stage. This map, paired with field specific conditions will help assess your risk and make an informed decision on whether or not you should apply fungicides.
Even if all sides of the disease triangle are present, it still may not make economic sense to spray. It is important to balance the cost of the fungicide and application costs with the expected yield and value of the crop. If the decision to spray is made, an appropriate fungicide should be selected and applied effectively. Fungicides registered for suppression of FHB can be found in the 2022 Guide to Crop Protection. Sprayer101.com has application tips and nozzle selection information available on their website.