Wheat School: Covering the flag leaf to manage disease and deliver yield


The flag leaf plays a key role in managing disease in the wheat crop.

On this episode of the RealAgriculture Wheat School, our resident agronomist Peter Johnson shares tips on identifying the flag leaf and how growers can use its emergence to guide their disease management strategy to protect yield at T2 timing (flag leaf) and T3 (when the emerging head fully clears the flag leaf).

How do growers know whether the flag leaf has emerged? In the video, Johnson shows how growers should look for the first node in the stem. The leaf attached to this node is considered leaf 4. Moving up the stem, growers can count the leaves in descending order — leaf 3, leaf 2 and leaf 1 — and then comes the flag leaf.

For a T2 fungicide application, especially in Western Canada where the crop is not sprayed at T3, the flag leaf should be fully emerged so the full leaf can be protected for maximum protection. (Story continues after the video.)

In Ontario, the winter wheat crop is typically sprayed at T3 to protect against fusarium. Johnson notes that a T3 application is not always required when disease levels are low. However, research from University of Guelph associate professor Dave Hooker shows that a T2 application plus a T3 application produces an additional 2.8 bu/ac gain yield.

“Most of the time, when there’s no disease, you would say that doesn’t make sense,” says Johnson. But in 2022, with wheat selling for $15 per bushel, “it might be worth chasing.”

Johnson also offers tips on T3 timing, noting that Day 1 of the application window is when 75 percent of the wheat heads have cleared the ligule of the flag leaf. He adds that Day 2 is “perfect timing” but T3 fungicides can be applied up to Day 8.

Click here for more Wheat School videos.

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