Wheat School: Protecting the flag and penultimate leaf from disease

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In Western Canada, spray 2019 is full speed ahead, and fungicide timing is at the forefront of many producers’ minds.

For a crop like wheat, it’s essential to stay ahead of leaf diseases to get the maximum yield output from your crop. Each leaf on a wheat plant provides a different contribution to yield, so there are certain ones you want to keep an eye on when scouting your fields.

Jeremy Boychyn, agronomy research extension specialist with Alberta Wheat and Barley Commissions, tells RealAgriculture’s Kara Oosterhuis in this Wheat School episode, the most significant contribution to yield is the flag leaf. (Story and visuals continue below video)

“The flag leaf is the leaf that comes out before your head comes out, and then the penultimate leaf is the one that’s below that. The flag leaf contributes about 40 to 45 per cent (to the yield), and the penultimate leaf is in the 20 to 25 per cent range. The head of the wheat plant only actually contributes to that 20 to 25 per cent range as well.”

When scouting for disease, Boychyn notes it’s important to keep an eye on the amount of moisture that is on the ground and to make sure you are looking through the canopy to check for any disease spots.

“So you’re digging in the bottom of the canopy because that’s typically where you’re going to get the most amount of moisture, and you’re going to get the most disease showing up first. That’s because these diseases typically come from trash and residue on the ground from previous crops,” he says, adding it’s imperative to get out and spray your fungicide before the disease gets to the flag or penultimate leaf.

When it comes to making those fungicide decisions, Boychyn says the typical rule of thumb is that “20 per cent of disease coverage takes about 10 per cent away from yield.”

Boychyn acknowledges that a foliar disease such as stripe-rust is a bit different, because of its aggressive nature.

“You really want to be on the ball if you are hearing of rust in your area. Hopefully, you are looking at the wind trajectory forecasts that are coming in for Alberta to see if we are having rust spores coming in,” he emphasizes.

“Then if you are seeing those moist conditions in your field, you want to be out there, making sure that you are checking in your fields and seeing whether you are having any progress at all, because if you see a little bit of rust at all in your field, even five per cent leaf coverage, that’s enough of a threshold for you to want to spray.”

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