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Crop Advisor’s Casebook: The case of the yellow-tinged spring wheat

A Crop Advisor's Solution from the December 5, 2017 issue of Grainews

Not only were Rob’s wheat leaves yellowing (chlorotic), but their centres 
were forming bands.
Gary Demoskoff. photo: Supplied

In June 2016, I had an interesting situation arise when Rob, a Brunkild-area producer, called me about his yellowing red spring wheat crop. While out scouting his other fields for crop staging, Rob noticed one of his wheat fields, which he had sprayed with herbicide a few days earlier, had a yellow tinge to it.

After walking into the field from the headlands, not only did Rob notice the wheat leaves were yellowing (chlorotic), but their centres were forming bands. Also, the fact that his headlands were showing no signs of these symptoms was odd, he thought. Rob asked me if I could explain such a phenomenon. Because I didn’t have an answer for him, within minutes I was on my way to Rob’s farm.

As Rob and I approached the field, I could see the yellowish tinge to the crop. I also noticed the headlands looked healthier than the rest of the field.

“My wheat seems to be yellowing, but my headlands look okay,” Rob said. “Could it be a fertility problem?” he asked. “If so, how come my headlands are different?”

These were excellent questions that needed answers. But first, a good look at the crop was in order. As we walked into the field, I noticed the plants with chlorosis formed a distinct square in the centre of the field, while the plants on the headlands were green and healthy. In addition, bands were forming in the centre of the leaves on the affected plants — this also struck me as odd.

In general, the growing conditions prior to spraying were excellent with adequate moisture, so not only was the wheat growing at a rapid pace, but the weeds were as well.

A few days prior to my visit, Rob applied herbicide to this field. He told me the first few rounds were sprayed with registered products left over from a herbicide application on another wheat field. After that, he said he filled his sprayer tank and continued to spray the same chemistries on the field in question.

After checking Rob’s fertility plan, I doubted we were dealing with a nutrient deficiency.

“Could the issue be chemical damage from herbicide applications on surrounding crops?” asked Rob.

This, too, was not the case. Spray drift could be ruled out because of the distinct square pattern to the damaged area. The square was made up of damage plants surrounded by healthy plants on the headlands. Plants injured by herbicide drift create an irregular pattern rather than one with straight lines or a geometric shape.

Something was just not adding up.

“Is there anything you could have left out chemistry-wise?” I asked him.

A slow smile spread across Rob’s face. I knew he had the key to the casebook.

“I did forget to mention something…,” said Rob.

Crop Advisor’s Solution: A stimulating situation: rapid plant growth and herbicide injury

After some thought, Rob remembered the tank mix left over from spraying the previous wheat field contained a biostimulant. With that little piece of information everything fell into place.

Because of the favourable conditions, plant growth that season had been rapid. This rapid growth can inhibit a plant’s ability to metabolize herbicide, thus causing injury to the plant. Specifically, the graminicide portion of the herbicide is trapped in the plant causing the leaf yellowing and banding.

The plants on the headlands weren’t injured because the area was treated with a biostimulant when Rob sprayed out the remaining tank mix from a previous field. Biostimulants can improve plant metabolism efficiency, thereby reducing the effects of herbicide injury.

Although rapid plant growth can cause herbicide injury, it doesn’t happen often and really depends on environmental factors, crop stage and the herbicide used.

I consider this case a success story as Rob learned, although uncommon, herbicide injury can occur during rapid plant growth due to excellent growing conditions. Furthermore, he witnessed first-hand the efficacy of biostimulants, which are attracting a great deal of attention these days.

Gary Demoskoff, CCA, works for Richardson Pioneer Ltd. in Brunkild, Man.

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