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Crop advisor casebook: What caused the colour banding in this wheat field?

A Crop Advisor's Solution from the February 19, 2019 issue of Grainews

Jacey Schettler.
photo: Supplied

One morning last May, I received a call from Dale, a farmer in Westbourne, Man., who farms around 3,500 acres of canola, wheat and soybeans. He told me he had been out walking his fields and noticed “striped” wheat plants.

He said the striping, which appeared as yellow bands on the first and second leaves, was found in the field between May 20 and 22. Frost immediately jumped to my mind as a possible culprit.

“It can’t be frost, we haven’t had any since the wheat emerged. It’s been a tad chilly at night, but hasn’t dropped below freezing,” Dale told me, before adding: “I think it’s some sort of nutrient deficiency.”

I drove out to his place and immediately saw the yellow banding he was talking about. The first and second leaves of the plants were banded with anywhere from one to three rings of yellow.

I didn’t think it was a nutrient deficiency — we had conducted a soil sample on that field that fall and had fertilized accordingly. No in-crop herbicide had been applied yet, so I was able to rule out issues associated with a herbicide application.

photo: Supplied

Overall, the plants looked healthy; despite the cool nights, they were enjoying some nice warm days of around 25 C that week. However, I noticed the plants that were affected by the colour banding appeared to be a bit thinner and more spindly-looking than the unaffected plants.

To me, the only possibility left was a weather event, but Dale had already said there hadn’t been frost. Still, colour banding commonly occurs when there has been a temperature extreme. I pulled out my phone and checked the recent weather data, but it confirmed that no frosts had taken place since the wheat emerged. I inspected the plants more closely and found no necrotic tissue, which is also typical following a frost event.

In my mind, the issue had to be related to weather, but what exactly, and why were the plants reacting this way?

Crop Advisor’s Solution: Ensure consistent seed depth to avoid uneven emergence

Something jumped out at me. The wheat plants affected by the colour banding appeared to be a bit thinner and more spindly-looking than the ones not affected. Upon digging into the soil, we discovered that the affected plants had been seeded around three inches deep, while the others were seeded closer to the surface.

Colour banding is mostly benign. It can often be attributed to cold nights and sunny mornings in the early phases of plant growth. We had ruled out frost, but we looked at weather patterns from the past week. The area had been experiencing some extremely warm days (25 to 30 C) followed by a couple of cooler nights in the 4 C range.

This made sense. Colour banding can occur when we see large fluctuations in temperature at the soil surface during emergence. As the plant gets older, it is more cold-hardy and less sensitive to these extreme temperature fluctuations.

Because some of the wheat had been seeded deeper, it hadn’t matured as quickly and as a result was more sensitive to the hot days and cool nights. This explained why only the first and second leaves of these plants were affected.

The good news was the crop grew out of it very quickly with no lasting damage and no yield lag.

Since the colour banding only occurred on the smallest plants that were seeded a little too deep, I advised Dale to double-check the depth of seed on every row to ensure even seed placement and emergence. This should allow for a more even stand and stronger, more weather-tolerant plants.

It was also a good lesson that it pays to eliminate every possible cause until you discover the culprit. Like Sherlock Holmes said, once you eliminate the impossible, whatever remains must be the truth.

Jacey Schettler works for Richardson Pioneer Ltd. in Dundonald, Man.

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