Crop advisor casebook: Why the deformed canola and purpling leaves?

A Crop Advisor's Solution from the March 9, 2021 issue of Grainews

The affected canola plants had parts of their stems pinched off and were kinked over about six inches from the top. Symptomatic plants and others around them also had purpling leaves.
Nathan Zilinski. photo: Supplied

In mid-July, I received a call from Carl, a grain farmer located near Onoway, Alta., who was concerned about disfigured canola plants in one of his fields.

“It’s not a disaster yet and it seems to be happening in just one field, but I’d like to solve the issue before it gets any worse,” he said.

When I came out to have a look at the field with Carl, I observed the crop was mostly in the early flowering stage with a few straggling plants still bolting. As we walked through the field, I could see the deformed canola Carl was talking about — the plants had parts of their stems pinched off and were kinked over about six inches from the top. I also observed that the symptomatic plants and others around them had leaves that were purpling.

The plants with ribbon stemming symptoms appeared to be scattered randomly throughout the crop. In the worst-hit areas, about one in every 200 plants seemed to be affected, while other areas appeared to be untouched.

After repeated rains in the area that spring and flooding across the field, Carl wondered if what we were seeing could be a stress response to the excess moisture. My thought was although there were plants exhibiting symptoms of moisture stress spread around the field, there was clearly something more at work with those plants with the pinched stems.

Carl and I also discussed the potential for a disease infection that may have occurred in the field due to the perpetually wet conditions throughout the spring and early summer. Although this did seem like a possible explanation, the symptoms didn’t match any of the common diseases of canola in the area.

To rule out a herbicide-related issue, I started asking Carl about his sprayer cleanout processes and the field’s herbicide history that season and in previous years. Between the herbicide history and the seemingly random pattern of affected plants in the field, we agreed this likely wasn’t the case.

There was one important clue, however, that led me to suspect what could be causing the disfigured canola. To be sure, I sent some plant samples off for tissue analysis and when the results came back, it confirmed my diagnosis.

Crop advisor’s solution: Calcium deficiency responsible for disfigured canola

While examining the symptomatic canola plants, I had noted they had purpling leaves, as did most of the other plants in close proximity to them. This was an important clue, as I knew this kind of discolouration can be caused by a nutrient deficiency. Tissue samples sent off to a lab for testing confirmed the plants with ribbon-stemming symptoms were deficient in calcium.

Given that the soils in this area are generally calcium rich, Carl found this somewhat surprising, especially since previous soil samples had confirmed that calcium levels in the field were high. Clearly, however, the crop was not accessing this nutrient properly.

There are a few reasons why this may have been the case. Calcium can be susceptible to leaching and the repeated precipitation in the spring may have caused calcium in the soil to leach out of the root zone and become unavailable for some plants to take up.

In addition, root development and overall plant health were negatively affected by the excess moisture, which also likely contributed to the problem. Shallow, stunted roots or damaged root tips would reduce root exploration for nutrients and the uptake of all nutrients, including calcium. The high relative humidity associated with the rain could have contributed to the reduction of calcium uptake as well due to a reduction in transpiration.

Upon receiving confirmation of the calcium deficiency from the lab, Carl and I discussed the next possible steps to correct the issue. Fortunately for the grower, in the week that had transpired since my initial visit, the field had dried out quite a bit and the conditions had not continued to worsen.

Given the crop staging, a granular fertilizer application was likely to be ineffective, so we discussed the option of using foliar fertilizer product containing calcium instead. Ultimately it was decided that given the overall crop condition and the amount of the field affected by the calcium deficiency, it would not have been economical to make the application.

At harvest time, we felt there was a small yield penalty in the most affected areas of the canola field, but it wasn’t enough to have warranted applying fertilizer. Going forward, Carl plans to focus on managing nutrients proactively as much as he can by monitoring the nutrient levels in the soil and in plant tissues and taking corrective action when necessary.

The experience was a good learning opportunity to remind us all nutrients are important for proper plant development and that there are scenarios where a nutrient like calcium can be abundant in the soil but not necessarily available to the plants at a given point in time.

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