Crop advisor casebook: Why did this barley field turn yellow almost overnight?

A Crop Advisor's Solution from the March 23, 2021 issue of Grainews

Jackie Medvid. photo: Supplied

Driving through lush, green farmland near Elfros, Sask., one day in July, I had a peaceful, easy feeling as I watched a gentle breeze rock the growing crops back and forth in the passing fields. It was a perfect summer day, one that farmers and agronomists dream about.

The dream came to an abrupt halt as I pulled up to a barley field that Sam, a customer of mine who runs a 4,000-acre mixed grain farm, had called me about.

It had been a dry spring but farms in the area were doing relatively well. In the past week there had been a substantial amount of precipitation, which had perked up crops, but that wasn’t the case in this field.

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“We have a big problem here,” said Sam, pointing to a glaring patch of discoloured barley plants. “I have never seen anything like this, ever. It’s like almost overnight they turned yellow.”

As I surveyed the barley crop, it was clear the yellowing wasn’t consistent across the field but was limited to some areas along the main grid which, to Sam’s chagrin, were in full view of his neighbour’s critical eyes. When I inspected some of the affected plants, other symptoms were revealed — leaves that were necrotic and leaf tips that were turning brown.

Sam had grown barley before, but this was the first time he’d tried this new feed variety. Sam told me he thought the disease package on the variety was decent, so he was surprised to see what he believed could be a disease outbreak in the field.

As the two of us walked through the damaged crop, Sam continued telling me about the history of the field.

“I always fertilize macros for what the crop needs, and since I started broadcasting my micro blend containing zinc, boron and copper, the yields have been terrific across the farm. This field, though, has been nothing but trouble,” Sam said.

“I couldn’t spray it two years ago because it was too darn wet. I’ve been playing catch up on weed control ever since, and now this.”

Sam thought he had finally got a grip on the weeds after applying a comprehensive weed management program that incorporated residual and multi-mode of action herbicides.

Because I’d never seen anything like this before, I decided the best strategy was to get tissue samples from some affected plants tested. I told Sam I thought that should provide an answer to the mystery of what was going on with his barley crop.

“Now that’s what I like to hear,” Sam said. “As the saying goes, I have to stay optimistic or else I wouldn’t still be farming!”

Crop Advisor’s Solution: Excess boron to blame for barley yellowing

The lab results of the affected tissue samples we sent for testing revealed boron toxicity was the most likely culprit for the yellowing barley, since it was in the very high range with 214.4 ppm.

Boron was one of the micronutrients Sam had broadcast over the barley field earlier in the season. Boron is mobile in the soil, and it appeared the substantial precipitation after the nutrient was applied had pushed the boron deeper into the plant’s root zone, causing the affected barley to turn yellow later in the season.

Excessive boron also causes stem elongation, which could explain why the symptoms had become much more noticeable in what seemed like very little time.

After discussing the results of the tissue tests, Sam and I agreed the best course of action was to monitor the issue with further testing. I was able to get back out to the field after another big rain- storm to collect more tissue samples, and this time the testing showed the amount of boron in problem areas of the field had climbed to 366.0 ppm.

At this point, there wasn’t anything that could be done to correct the boron toxicity issue. Fortunately for Sam, it was limited to only certain parts of the barley field and it didn’t turn out to be a huge yield drag come harvest time, as the crop yielded very close to that of his other barley fields, which showed no symptoms.

As this case shows, boron toxicity symptoms can be very irregular across fields. In this instance, though, the problem was com- pounded by an operator error, which I learned about after a discussion with Sam. It turned out when Sam had applied boron and other nutrients to the barley field, he’d been trying out a brand-new floater he’d just purchased and was adjusting application rates on the fly. This led to overapplication in some areas, which was obviously detrimental to the crop.

After acknowledging his mistake, Sam was able to laugh about it — joking he should refrain from operating any equipment that was less than 20 years old from now on, and that Toby, his 12-year-old, more tech savvy son, should be put in charge of running the newer equipment on the farm.

Jackie Medvid, CCA, TechAg, works for Richardson Pioneer Ltd. in Foam Lake, Sask.

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