Crop advisor casebook: Emergence issues in canola

A Crop Advisor's Solution from the June 2, 2020 issue of Grainews

Jaime Barton.
photo: Supplied

Joe, who grows canola, wheat, barley and lentils on his farm near Delisle, Sask., called me in early May about an alarming problem that, in just a few days, had turned a promising-looking canola field into an eyesore.

Joe had finished seeding his crops and was checking his fields for emergence when he spotted the trouble. Things were looking good the last time he’d checked his canola field, but now it was a much different story — not only was emergence very patchy overall, but there were also large areas where no canola was growing at all.

The grower was at a loss to explain what had happened and he was hoping I could help. I told Joe I’d head out his way to see what I could do.

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As I drove up to the canola field, it was clear the crop was in bad shape. I could see lots of bare patches and all kinds of inconsistent emergence that gave the field a stagey appearance.

After shaking hands, Joe told me he was considering reseeding the field, but he wanted to get to the root of the problem first to avoid having it happen again. We also had to determine if the overall plant stand warranted a reseed.

Joe wondered if it might be an issue with his seeder or, since it had been a cool, dry spring, whether insufficient soil moisture might be to blame.

“We seeded canola first because it was our best shot at getting the canola into moisture, but maybe it wasn’t deep enough or the soil dried out after seeding,” he said. I told Joe those were possibilities and that I’d have a better idea after inspecting the field.

When I went into the bare spots and started digging around, there were many areas where I couldn’t find a single seed. However, what I was seeing didn’t appear to be consistent with a seeder miss or a seed depth issue, so I considered whether the problem might have something to do with residue management.

Seeding with a disc drill into heavy stubble can cause hair-pinning of residue and poor seed germination as a result. However, there wasn’t that much residue that I could see anywhere in the field, so I figured the answer had to lie elsewhere.

The possibility of insect damage crossed my mind, but I couldn’t find any destructive pests like wireworms or signs of insect feeding such as chewed stems or chopped off plants.

While walking around the field, I had noticed that the bare patches were situated in low spots. The field did appear to be drying out, particularly in high spots, but in the low areas with missing plants there appeared to be adequate soil moisture, so this wasn’t the answer either.

Due to the dry conditions, I wondered if fertilizer burn could be to blame. However, that was ruled out when I learned the product Joe had applied to the field had been put down at a safe rate.

Joe raised the possibility of herbicide carryover, but if there were plants showing these kinds of symptoms in the field, I hadn’t seen any. I also didn’t see anything to be concerned about when Joe and I discussed the spray history of the field.

I didn’t have the answer I was looking for yet, but I knew where there was one other possible explanation for Joe’s eyesore of a canola field.

Crop Advisor’s Solution: Frost found to be the culprit in canola case

The worst-hit areas were in low spots, which are the areas in a field where cold air will typically settle. I remembered there had been a frost warning several nights earlier — that’s when everything clicked.

I began searching these areas for plants with frost injury symptoms and was able to locate a few small seedlings that were shrivelled up or had been pinched off. I realized because the frost had occurred a few days previously, many of the canola seedlings affected by it had in all likelihood already died, which would explain why our search for seeds in the bare spots of the field had been unsuccessful.

Now that we had an explanation for what had happened, Joe and I discussed what to do next. Reseeding those parts of the field with the most frost damage was one option, but I suspected without reseeding the entire field, this would likely end up damaging the crop in other areas that had fared better. Since, on average, the field still had more than the one to two plants per square foot threshold, the decision, then, was to hold off and see how well the canola crop recovered from the killing frost.

After a couple of weeks, Joe saw more canola come up and the field ended up filling in better than expected, other than one or two small areas in the low spots, which didn’t come back at all. At the end of the season, Joe was happy to report that his canola field had produced a higher-than-average yield.

Joe realized if he’d waited a little while to seed the field, this could have prevented the frost damage to his emerging canola crop. My advice to him was to hold off seeding his canola fields in the future until the weather warms up a bit and frost warnings are less likely, although this is obviously dependent on how large the window for planting is in any given season.

The frost incident did provide a valuable lesson for Joe — that canola is a very forgiving crop and it can make up for a really low, early-season plant count quite easily, if growing conditions are good. Evaluating plant establishment throughout the early stages of the crop is important, especially a few days after a potential frost event, as it can take some time before the damage is fully evident.

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