Crop advisor casebook: Wheat crop takes sudden turn for the worse

A Crop Advisor's Solution from the September 22, 2020 issue of Grainews

Ash Klassen.
photo: Supplied

In late July, I got a call from John, who grows wheat, barley and canola on his farm near Nampa, Alta. His wheat crop had gone from fine to funky in the span of a week, and he was hoping I’d be able to tell him why.

When I arrived at John’s farm to check out the wheat field, it was clear the crop wasn’t in good shape.

The plant stand was thinning in some areas and there were numerous patches where the plants were ripening prematurely. Some of the affected wheat had kinked heads, discoloured heads, or partial heads with aborted spikelets, and I also observed pigtailing of the leaves in affected plants.

According to John, all the symptoms had developed very recently as it’d been a good-looking wheat field just one week before. I began weighing different possibilities for what had made things take such a sharp turn for the worse.

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I started by scanning the field for patterns that were indicative of mechanical damage, but I found none.

Fusarium head blight crossed my mind as a possible cause, as the area had received average precipitation so far that year with no excessively dry or wet periods, and slightly warmer than average temperatures that could have bumped up humidity levels a bit.

I needed more information to make an accurate diagnosis though, so I asked John about the history of the field’s fertilizer and crop protection applications over the past three years. I also reviewed soil sample data John based his fertility program on.

At this point, I began to suspect what was causing the symptoms in John’s wheat field, but it took some additional plant tissue testing to confirm my diagnosis.

Crop advisor’s solution: Wheat plants severely deficient in copper

I suspected a nutrient deficiency could be the culprit. However, when I checked out John’s fertility program for the field, which was based on soil sampling from the previous five years, everything looked fine and the soil sample reports themselves revealed no obvious deficiencies.

I decided to send some plant tissue samples in for testing to assess the current nutrient situation, and the lab results provided our answer — the wheat plants were severely deficient in copper.

I determined that even though soil sampling showed the copper levels in the soil were well within the sufficient range, there had to be something tying up the plants’ access to the nutrient.

A review of the soil samples revealed a high organic matter content. Organic material binds to copper more strongly than any other micronutrient, which could have contributed to the plants not being able to access enough copper. This was not a supply issue but an availability issue with the copper in the soil.

Unfortunately, there was little John could do for his wheat crop this late in the season. At harvest time, the yield was below average and the kernel size and weight were also less than ideal, but at least it wasn’t a total crop failure.

Going forward, I recommended John keep a closer eye on his crop earlier in the season, which would give him more time to take corrective action should there be any signs of a nutrient deficiency.

I also suggested John apply a granular or liquid copper product as part of his spring fertilizer program and that he also consider doing plant tissue testing in season to monitor copper levels.

As I indicated to John, soil sampling is an important tool for assessing nutrient needs but incorporating tissue sampling as well can provide a more complete picture of nutrient availability in a field.

Ash Klassen, CCA, RTAg, works for Richardson Pioneer Ltd. in Nampa, Alta.

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