When thinking about protecting yield from disease, one of the first things to understand is where yield actually comes from.
Jeremy Boychyn, agronomy research extension specialist with Alberta Wheat and Barley Commissions, understanding how the each leaf of the wheat plant builds yield helps inform decisions on how to best manage risks to yield.
“One of the common themes we talk about is flag leaf versus penultimate leaf, versus antepenultimate leaf. And what we’re talking about there is essentially, the flag leaf is at the top leaf of the plant. It’s the last leaf that comes out before we see head emergence. The penultimate is essentially the next leaf down from the flag leaf, and then the antepenultimate would be the third leaf down. And then there’s F4, which would be the lowest leaf before we get into the tillering leaves,” he explains.
When thinking about yield contribution, each of these leaves each contribute a different amount to the final yield, which is why fungicide timing, especially, can become crucial if disease threatens the top two leaves.
Check out the video below, where Boychyn walks us through each leaf and its contributions:
“The head actually contributes about 20 per cent of the yield with photosynthetic area,” he explains. “The flag leaf of the wheat plant is in that range of 40-45 per cent yield. And then we get into the penultimate being in that 20 per cent range. And the antepenultimate is more in that 7 per cent range.”
Knowing where yield comes from helps knowing where to protect the plant at each stage, however, as Boychyn notes, always consider the disease triangle before heading out into the field with the sprayer.
The disease triangle is key: do we have the host, do we have the disease, and do we have the environmental conditions for that disease to flourish? These questions need to be asked in light of yield potential.