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Crop Advisor’s Casebook: Yellowed sixth and seventh barley leaves tell a tale

A Crop Advisor's Solution from the April 18, 2011 issue of Grainews

The youngest leaves were most affected and were severely yellowed in this barley crop.

As Rodney drove by his field mid-June last year, he got a nasty shock. His barley crop — progressing well up until that point —was turning yellow. “I’ve never seen this in my 20 years of farming,” Rodney told me. “My barley crop is under a lot of stress,” he said.

Rodney farms 1,000 acres of barley and canola near Clanwilliam, Man. Overall, he said, the crop looked unhealthy, and he wondered if a nutrient deficiency was causing his plants to yellow.

At his request, I travelled out to Rodney’s farm to offer him some advice and recommendations.

Generally, his plants looked stressed, and I noticed the leaves were turning yellow. The youngest leaves were the most affected and were severely yellowed. Also, brown spots were present on the lower leaves.

We scouted his crop together, determining the symptoms were uniformly distributed throughout the field. From my initial survey, there were a few possibilities for the source of the problem.

Rodney wondered if nutrient deficiency was playing a role. It was a good theory, and we would explore that avenue. Precipitation had been heavy that spring, so stress due to excessive water was also high on our list of candidates. Rodney rotated canola and barley on his farm. This tight rotation ups the ante on disease-pressure risk and could be stressing his barley.

To the west of Rodney’s farm, his neighbour was growing glyphosate-tolerant canola. Just before the symptoms appeared in Rodney’s field, his neighbour completed his spraying. There was a possibility drift from the application of herbicide to his neighbour’s field was causing the stress on Rodney’s crop.

Rodney had sprayed his field with a Group 1 herbicide and registered tank mix four days before the symptoms appeared. I thought we’d better take a closer look at Rodney’s own application of herbicide before we talked to his neighbour about drift.

One by one we eliminated the possible causes of damage to Rodney’s crop. Barley plants that are deficient in sulphur will yellow in the same manner as Rodney’s plants. And, like Rodney’s plants, the yellowing is usually more pronounced in the younger leaves of plants with a sulphur deficiency. But the results of a tissue test revealed adequate sulphur levels and eliminated a nutrient deficiency as the cause of Rodney’s unhealthy crop.

Stress due to water could also be crossed off our list because barley growing in areas with good and bad drainage presented the same symptoms.

Before we talked to his neighbour about herbicide drift, I investigated Rodney’s records and calculations for his own herbicide application to his barley field. I checked the amount of herbicide Rodney purchased that spring and the rate of application he used — everything was correct. He had also flushed his tank thoroughly before application, and he used the correct registered tank mix. The environmental conditions were good for spraying that day — warm, overcast, little wind and no rain.

I went back to his field and pulled up some of the barley plants, inspecting them more closely. The barley’s flag leaf was emerging and nodes were present. Also, the most severe yellowing occurred on the sixth and seventh leaves—now I had my recommendations for Rodney because I knew what was causing the problems in his field, and it wasn’t his neighbour.

Crop Advisor’s Solution: Ill-timed herbicide set back this crop

When I examined the plants I noticed the flag leaf was emerging and nodes were present. Also, the most severe yellowing occurred on the sixth and seventh leaves. I knew then that we were dealing with a timing issue. The recommended guidelines for that particular herbicide are to spray up to the fifth leaf stage, with the optimal stage to spray at three to four leaves. Rodney had sprayed after the fifth leaf stage — the sixth and seventh leaves should not have been present when applying this Group 1 herbicide to barley.

It’s amazing how overlooked, yet important, crop staging is. Crop protection guides, advice from your local agronomist, as well as careful consideration of the guidelines and application instructions on crop protection product labels are all resources producers can turn to for help when applying crop protectants.

Applying herbicide at the wrong stage stressed Rodney’s barley, causing it to yellow. That stress made his already damaged crop more susceptible to fungal infestation. I recommended Rodney apply a fungicide to pre- vent the disease from getting worse while his crop recovered from the stress caused by the staging error.

In the end, Rodney was a happy customer. The fungicide helped prevent more disease and the plants recovered enough to yield an average crop. Rodney and I are keeping in touch this spring on agronomic issues, strengthening our business relationship and, hopefully, improving Rodney’s yields.

Stephanie Richards is a location assistant at Richardson Pioneer Ltd. in Minnedosa, Man.

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