Wheat School: Checking the peduncle and kernel ahead of a pre-harvest glyphosate pass

Cooler temperatures across Western Canada have brought about some challenges — one of them being a delay in wheat maturity. Crops are at variable stages, even within a single field.

Producers considering a pre-harvest glyphosate application on the wheat crop are faced with a tough call — some of the crop is ready, and some isn’t. What’s a farmer to do?

As Jeremy Boychyn, agronomy research and extension specialist with Alberta Wheat and Barley Commissions, explains in this Wheat School episode, you have to pay attention to the least advanced part of each field.

“You’re going to go to the least advanced part of your field, and the first thing you’re going to do is look at the peduncle — which is the area of the stem below the head, at the top of the stem. If that stem has turned from green to yellow, it’s no longer translocating energy from the bottom of the plant up into the head. So what this means is if you apply glyphosate onto that plant, it’s not going to be moving it up as quickly,” he explains.

Looking at the peduncle is just one part of the equation, and as Boychyn notes, you still need to take a look at the kernel. (Story continues below video)

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“If the kernel is above 30 per cent (moisture) it still is able to take in some of that glyphosate that you apply,” he says.

After assessing peduncle colour, farmers should grab a few of heads and hand-thresh them. “The next thing you are going to do is the thumbnail test. So you’ll squeeze it in between your finger and your thumb, and if that kernel just squeezes, and you can squeeze it down and it mushes, it’s definitely where you want it to be. You want it to be solid, and when you push your thumbnail into there, you should get that thumbnail to indent, and stay in that kernel. If it pushes back out, you’re not at 30 per cent yet,” Boychyn says.

When it comes to the pre-harvest interval — the time from a product application to cutting the plant stem —  it’s essential to keep in mind that not all glyphosate formulations have the same recommendations. Producers need to read the label of the specific product they use. It’s also imperative to know that there is a difference between a desiccant and a pre-harvest herbicide. In the case of a glyphosate, a herbicide, it’s used for cleaning up the field and preventing the weed-seeds from spreading.

“You’re looking for perennial weeds; thistles, perennial sow thistle, and potentially any annuals you are worried about going to seed. That’s what you’re going in there and getting an idea of. If you do decide that you want to use glyphosate to control some of those weeds, then you’re making sure that it’s timed appropriately for the least-advanced part of the crop. That’s the general approach you want to be taking with glyphosate when you are using it as a pre-harvest (management tool),” Boychyn explains.

There are dangers to applying glyphosate too early, as it could create a market access issue, so keeping these tips in mind during the harvest season is key to successful years to come.

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