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Crop advisor’s casebook: What’s causing the half-circle pattern in this wheat field?

A Crop Advisor's Solution from the November 6, 2018 issue of Grainews

Cheryl Westman.
photo: Supplied

John is an Alberta producer who has a mixed farming operation located north of Vermilion. His main crops are wheat and canola. John called me mid-June this year to examine his wheat crop after he noticed some patches in the field’s outside rounds were slowly dying.

As I approached the field, I could see what looked like half circles of dying wheat. The plants’ leaves were brown, crisp and dying in these areas. The damage occurred periodically in the outside rounds.

Closer examination revealed the plants were at the four-leaf stage with one or two tillers, and were already quite large. Additionally, the leaves were starting to burn on the tips and the roots were shrivelling up.

“I may have seeded too deep,” said John. “Or the air seeder malfunctioned.”

In addition to John’s theories, a few factors I thought could’ve caused this damage were an in-crop herbicide injury, fertilizer burn or environmental stress.

John’s machinery was set correctly and was performing normally. The plants were also seeded at the correct depth, confirming the damage wasn’t caused by seeding issues.

It was easy to eliminate in-crop herbicide injury as one of the factors causing the damage because John hadn’t made any applications of this type yet.

The plants on the outer edges looked healthier than the ones inside the half circles, which were dying faster — the roots of those plants were more shriveled and the leaves more burned.
photo: Supplied

John’s fertilizer application rates were all correct, allowing us to conclude fertilizer burn was not the issue.

The region’s growing conditions were somewhat challenging this year. It was a dry spring and this field hadn’t had rain for about a month. Could the damage be caused by environmental stress? If that was the case, I’d expect to see more damage throughout the field. However, the dry conditions could be playing a role somehow.

I examined the plants in the damaged areas in more detail. The plants on the outer edges looked healthier than the ones inside the half circles, which were dying faster — the roots of those plants were more shriveled and the leaves more burned.

John and I examined the field’s records from 2017. We found the piece of the puzzle we were looking for.

Crop Advisor’s Solution: Apply herbicides correctly in the fall to save your yield

The dry conditions the previous fall continued into the spring. This field hadn’t received any precipitation for about a month. I thought the dry conditions were exacerbating some kind of herbicide injury.

We examined the field’s history for 2017, which revealed the damage source. Last fall, this field received a custom application of a Group 8 herbicide, which caused chemical residue injury to the plants in certain areas of the field.

Tissue sample results confirmed this hypothesis. The Group 8 herbicide applied to the field was floated on the previous fall, and there were some areas where the custom applicator hadn’t turned his booms off when he turned at the end of the field.

The spray overlap and the dry conditions resulted in the plant damage when the roots reached the Group 8 herbicide in the soil profile.

If John decides to apply a Group 8 herbicide to his fields in the fall again, he will instruct the custom applicator to shut the booms off when turning at the end of the field so no overlapping of chemicals occurs.

Although the wheat plants did die in these areas, the effect on yield was negligible.

Cheryl Westman works for Richardson Pioneer Ltd. in Vermilion, Alta.

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