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Casebook: Canola conundrum

Last June, Landon, a local producer, walked into our Ag Business Centre at Strasbourg, Sask., carrying a handful of feeble-looking canola plants. “Something’s affecting the vigour of my canola. Could be low fertility, or maybe a disease. I also heard some rumours about insects damaging canola in the area,” he said. He set the yellow and wilted plants on my desk. “I thought you might be able to tell me what’s going on with these plants,” he said.

On these sample plants from Landon’s field, I did find some cabbage root maggots and a wireworm. Root maggots are usually found in cool, moist soils in June and July. The maggot creates tunnels in the canola root, and severe tunnelling can reduce plant heath, resulting in the stunting of growth, yellowing of leaves and early plant death. However, slight feeding of root maggots, as in this case, has very little effect on canola plants. As for wireworms, they aren’t common canola pests, and they don’t cause a lot of damage to the plants.

“I’d better come out and take a look,” I told him. “I don’t think these pests are your problem.”

Landon farms 2,000 acres of canola, pulses and wheat near Earl Grey, Sask. The field in question looked set back in its development when compared to Landon’s other field of canola across the road. The field appeared to be struggling. The plants were small, yellowing and wilting, like the ones he had brought to the centre.

I scouted for root maggots, pulling up plants and examining them for tunnelling, but I couldn’t find any other plants with root maggots — or wireworms, for that matter.

I compared the physical attributes of both canola fields. The soil texture and type was similar, and soil moisture was average, although there had been a fair amount of precipitation early in the spring, which had already dried up. However, the yellowing of the plants’ leaves in the affected field was more pronounced in low-lying areas, where extensive flooding had taken place that spring. Perhaps the excess moisture had stunted the plants’ growth and had caused chlorosis, I thought. But, if so, both fields would appear chlorotic, and this was not the case. Across the road, the plants were healthy, green, and growing at a normal rate.

A field’s history can reveal many clues when one is trying to determine the causes of an agronomic dilemma. Past activities can shape interactions and crop development. The histories of these two fields would eventually provide us with the answer we were looking for.

In the spring of 2011, Landon had planted both fields with herbicide-tolerant canola seed, although two different varieties had been used — glyphosate-tolerant canola, which produced the yellowed and wilted plants, and glufosinate-tolerant canola, which produced healthy plants. He’d applied the same fertilizer type and rate to both fields. It was when Landon told me what he’d planted the previous spring that I knew what the problem was.

In the spring of 2010, Landon had planted one field with wheat and the other with Clearfield lentils.

“Chemistry is the culprit here,” I told him.

Why are the canola plants in one of Landon’s fields yellow and wilting while in another field they’re thriving? Send your diagnosis to Grainews, Box 9800, Winnipeg, MB, R3C 3K7, email [email protected] or fax 204-944-5416 c/o Crop Advisor’s Casebook. Best suggestions will be pooled and one winner will be drawn for a chance to win a Grainews cap and a one-year subscription to the magazine. The reasoning which solved the mystery will appear in the next Crop Advisor’s Solution File. †

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