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Timing and Necessity for Fungicide Application on Wheat and Canola

By Carlie Bowditch, Agrology Student, Tisdale 

July 2018

Plant disease can have a negative impact on crop yield. In the northeast area of Saskatchewan, fusarium head blight on wheat and sclerotinia on canola are two diseases producers need to be knowledgeable about and prepared to deal with. The timing of fungicide application is crucial for functionality of the chemical. 

Wheat 

For control of fusarium head blight, wheat fields must be sprayed when 75 per cent of the heads on the main stem are emerged and when 50 per cent of the wheat heads are in flower.

When scouting for timing of fungicide application, walk past the headlands as they are the first plants to mature and will not be a fair representation of the field. Once in the field, observe the amount of plants that are headed out and flowering by visually surveying the area. Flowering plants can be identified by very small yellow flowers coming out of the end of the glumes on the wheat head. The wheat head will begin flowering with the middle glumes and finish flowering at both ends. At timing of application 75 per cent of the field should be headed out and 50 per cent should be beginning to flower. If the wheat is sprayed with fungicide before it is headed out, some chemicals will still be effective on leaf diseases such as leaf rust or stem spot. However, in order to protect against fusarium head blight the spray must come in direct contact with the head of the wheat plant. It is less likely that will happen if the flag leaf is blocking the wheat head from the fungicide or the head is still in the boot. Once the plant fully flowers, the glume is closed and fungicide no longer has effect. If the crop is not sprayed before the wheat heads are fully flowered and the disease is present, then the disease is trapped inside the glume and disease is untreatable.

The presence of disease impacting the wheat plant in the northeast region of Saskatchewan is and has been a significant threat for many years. The impact of fusarium head blight on wheat makes the application of fungicide to prevent this infection both profitable and necessary for control of the disease. 

Canola 

Sclerotinia can cause significant yield loss in canola; however, it can be controlled by a fungicide. The staging to apply a fungicide to control sclerotinia is critical because this disease starts in the flowers and is passed onto the other parts of the plant through flower drop. It is crucial the fungicide is applied to the flowers before they drop and infect the plant.

When scouting it is again important to walk past the headlands as they are more mature plants and will not be an accurate representation of the field. At time of application the field will be very yellow. Canola fungicide application timing, for sclerotinia, is between 20 and 50 per cent bloom.  At 20 per cent bloom, there will be no flowers dropped and no pods forming. At 30 per cent bloom, there will be a few flowers on the soil and the bottom branches will be starting to form pods. These are the most affective times to apply fungicide. The flower count on each plant should be around 20 to 50 flowers on the main stem.  

The application of fungicide on canola is a fairly new practice. Diseases such as black leg and sclerotinia continue to increase as the number of canola acres increase. The profitability of fungicide application is not as clear to determine as it is on wheat. Since the disease pressure varies year to year depending on environmental conditions, the profitability of applying fungicide also varies.

For both wheat and canola, the application of fungicide is a preventative disease control method. This means that the fungicide must be applied before there are visual signs of disease in the field. Crops can mature quickly and can move from 50 per cent to 100 per cent headed or 20 per cent to 70 per cent bloom within a week in the right conditions. Continually monitoring the crop stage for timing of disease preventing measures is a vital part of fungicide application. 

For more information contact your local Crops Extension Specialist or the Agriculture Knowledge Centre at 1-866-457-2377.

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