Uneven crops make pre-harvest staging more important

Uneven crop maturity could complicate pre-harvest applications this year, making field staging especially important as harvest approaches.

At Manitoba Agriculture’s weekly CropTalk webinar in mid-August, provincial cereal specialist Anne Kirk said excess moisture earlier in the season left some fields with greener, later-maturing areas, particularly in low spots.

WHY IT MATTERS: Applying pre-harvest products too early can reduce yield, increase residue risks and create market-access problems.

She said growers should base pre-harvest timing on the least mature part of the field, not the field average.

Pre-harvest applications should not occur until grain moisture is 30 per cent or less in the least mature part of the field, when the crop has reached physiological maturity and grain fill has stopped.

Applying a pre-harvest herbicide before that point could cut grain development short.

“We’d end up with some shriveled kernels and reduced yield,” said Kirk.

She advised growers to check several areas of the field, paying particular attention to greener patches, low spots and late tillers.

In cereals, one quick indicator is the peduncle, or stem immediately below the head. A yellowing peduncle suggests the crop is approaching maturity.

Growers should also hand-thresh kernels and check whether a fingernail indentation remains in the kernel.

At the soft dough stage, a fingernail pressed into the kernel will leave an indentation that gradually disappears after pressure is removed. Once the crop reaches hard dough, the indentation remains, indicating the kernel is at or near the 30 per cent moisture threshold.

Green tillers can complicate the decision. If they contain significant developing grain, Kirk said growers may need to wait rather than risk applying too early.

Weed control or dry-down?

Provincial weed specialist Kim Brown said growers should also be clear about what they are trying to accomplish before choosing a product.

Glyphosate is a pre-harvest weed-control tool, particularly for perennial weeds such as Canada thistle and quackgrass, rather than a true desiccant.

“If you want to desiccate a crop, which means to dry it down quickly, this is not your product,” Brown said.

Diquat (Reglone), by comparison, is used for rapid crop dry-down. Saflufenacil (Heat) can also speed dry-down and is often used with glyphosate.

Brown said timing remains critical regardless of product. Glyphosate and mixtures containing it still need to be applied after crop moisture falls below 30 per cent in the least mature part of the field.

“If they’re more than that 30 per cent moisture, then they will take that glyphosate into the seeds,” said Brown.

“We cannot have that.”

Market acceptance

Beyond staging and dry-down, growers also need to consider market acceptance.

Keep it Clean’s 2026 product advisory continues to list pre-harvest glyphosate as “do not use” for malt barley and “be informed” for wheat, oats and barley destined for food or feed markets. Saflufenacil also remains a “do not use” product for malt barley.

Keep it Clean has stressed that glyphosate advisories for cereals are tied to market acceptance rather than the absence of maximum residue limits.

Brown and Kirk both advised growers to check product labels, pre-harvest intervals and buyer requirements before application.

That is particularly important where crops are uneven, Kirk said, because the mature portion of a field can make a crop appear ready before greener areas have actually reached physiological maturity.

“It can definitely be more difficult to stage in years like this,” she said.