Crop advisor casebook: Is fertilizer burn yellowing this wheat crop?

A Crop Advisor's Solution from the May 14, 2019 issue of Grainews

After Tom’s in-crop herbicide application, he noticed his wheat crop was yellowing in patches and there was a reduction in plant stand. Damaged plants were stunted and their leaves were twisting and pinched off.
Delaine Feil. photo: Supplied

I received a call from Tom mid-June last year after he noticed his wheat crop was yellowing and there was a reduction in plant stand following his in-crop herbicide application.

Tom, who owns a 2,500-acre mixed farm in the Meadow Lake region, thought the stand loss could be the result of an injury from the fertilizer applied in a sideband at seeding.

“We’ve been seeing this for the past three years — right after I bought my new drill,” he said. “I’m positive it’s fertilizer injury. We’ve been adjusting the distance between the fertilizer and the seed, but we keep seeing the same symptoms.”

I made my way out to Tom’s farm. I wanted to see the plant symptoms for myself.

When I arrived at the field, I found the crop was a pale yellowish-green colour and the plant stand seemed marginal considering there was an adequate amount of moisture available to the crop.

The crop was a pale yellowish-green colour and the plant stand seemed marginal. The youngest leaves were pale green and were exhibiting interveinal chlorosis. The lower leaves and the tips of the newest leaves were starting to die off. photo: Supplied

The youngest leaves were pale green in colour and were exhibiting interveinal chlorosis. The lower leaves and the tips of the newest leaves were starting to die off. The injured plants occurred in patches throughout the field. In addition to yellowing, damaged plants were stunted and their leaves were twisting and pinched off.

Everything checked out with respect to Tom’s in-crop herbicide application. The herbicide was applied consistent with the label recommendations and there were no residual herbicides that had been applied to the field. Furthermore, the plants’ symptoms did not look like they had been caused by herbicide injury.

I asked Tom about his fertilizer plan. He had applied the same blend he does every year, including the years before he bought the new drill. Additionally, there was adequate distance between the fertilizer and the seed-row, allowing us to conclude the reduction in plant stand was not a result of fertilizer injury.

Tom wondered if excess moisture could have caused these symptoms in his wheat crop. The area had received a lot of precipitation, but it wasn’t enough to severely affect the entire region. In addition, neighbouring crops were managing the moisture just fine. Only Tom’s field was exhibiting symptoms.

“I’m stumped,” said Tom. I was not. It was very clear why Tom’s crop was experiencing these symptoms.

Crop Advisor’s Solution: Yellowish-green patches in wheat crop caused by copper deficiency

Once I confirmed Tom hadn’t applied any crop protection products that could produce these symptoms, I felt confident these plants were suffering from a copper deficiency. When I suggested this theory to Tom, he was doubtful.

“I don’t think it’s a copper deficiency. We sprayed a foliar copper product last year and we didn’t see a yield benefit,” said Tom.

We decided to send in samples from areas of the field that had both highly- and mildly-damaged plants for tissue tests. The test results confirmed a copper deficiency. The plants with the most severe symptoms were also the most deficient in copper.

Tom also had a number of soil test results from this field from previous years. These soil test results suggested a copper deficiency because they showed Tom’s field had high organic matter (eight per cent), which is one of the common characteristics associated with copper deficiencies.

It’s important to know the soil’s characteristics and the interactions that can take place within the soil. Soil texture, pH and organic matter are just a few factors to consider when you are concerned about micronutrient deficiencies.

By the time the tissue test results were available, the crop was starting to head out. We had missed the staging opportunity for foliar copper products.

Tom had stopped using granular copper five years ago because he felt he wasn’t benefitting from the fertilizer application. Since then, the soil reserves had been depleted and the crop was beginning to experience deficiency symptoms. These severe deficiency symptoms likely could have been avoided had he continued to consider copper in his fertilizer program.

Tom plans on adjusting his fertility plan this spring by adding copper fertilizer to his blend. We will continue to monitor nutrient levels with tissue tests and apply foliar nutrient products if necessary.

Delaine Feil works for Richardson Pioneer in North Battleford, Sask.

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