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Crop advisor casebook: The case of the ailing canola

A Crop Advisor's Solution from the January 19, 2020 issue of Grainews

Many of the injured plants had leaves turning dark-green to black in colour, while the leaves of others were a translucent yellowish-orange.
Darren Camm. photo: Supplied

Harry is a grain farmer from Elstow, Sask., who called me last year in mid-June to discuss one of his crops. He’d been out inspecting his canola when he saw there was a serious problem — fields that looked fine only a few days before were now littered with some very sickly-looking canola plants.

Harry was at a loss to explain what had happened, as only half of his six canola fields were affected, and the crop damage within those fields didn’t follow any discernable pattern.

I told Harry I’d come over right away to have a look. The affected fields were fairly close to one another, and as I walked through them, I observed many of the injured plants had leaves turning dark-green to black in colour, while the leaves of others were a translucent yellowish-orange.

As Harry indicated, the damage wasn’t consistent across the canola fields. Upon closer inspection, it appeared the worst of the damage was in areas of the field with heavy crop residue.

My first thought was the crop injury could have been caused by frost damage. However, Harry swore that couldn’t be the case since the electronic temperature monitor he keeps in his yard a kilometre away showed it hadn’t dipped below 1.8 C the last few evenings.

I considered whether herbicide drift could be the culprit but dismissed that idea when I learned most of the crops in nearby fields hadn’t been sprayed yet. Harry’s canola fields hadn’t been sprayed either, which ruled out sprayer contamination as a possible cause. There also hadn’t been any residual herbicides applied to the affected fields the previous year that could have caused this kind of damage.

What, then, was behind the crop injury in Harry’s canola fields? When I spotted some wilted alfalfa in a ditch, it led me to believe I had my answer.

Crop advisor’s solution: Late frost causes damage, worsened by heavy crop residue

Another important clue was the canola plants in low areas of the field with heavy crop residue had suffered the most damage. Here, the straw was acting to keep the soil cooler, which left the young canola plants more vulnerable to a killing frost. In other low areas of the field that had been tilled in the previous year, there was much less crop residue, so it had warmed quicker in the spring and was able to provide enough heat to protect the plants from the late frost.

It was clear the spreader/chopper on Harry’s combine hadn’t done a very good job of distributing the straw evenly across the canola fields. Straw expelled from the combine was only being spread 25 feet while the cut itself was 36 feet wide, causing the straw to accumulate in some places. The chopper blades also likely needed changing as the straw hadn’t been chopped very fine.

My diagnosis came as a surprise to Harry, who thought frost damage wasn’t possible, since the gauge he relied on to monitor temperatures had recorded an evening low just shy of 2 C. The gauge, however, was located in a yard about a kilometre away and wouldn’t account for the microclimate in Harry’s canola fields. Cool air sinks into the low areas of the field, causing variability in the crop injury across the field.

Fortunately for Harry, many of the injured plants were able to recover. Maturity was delayed five to seven days in the affected crop, but despite that, the fields ended up yielding almost as well as those that had been spared the frost damage.

In this case, Mother Nature was the driver of most of the crop injury seen in Harry’s canola fields. Although improved straw distribution could have improved the crop’s tolerance to the light frost, topography is something that cannot be overcome. In the future, Harry will be mindful of seeding date of his canola and will be more informed of the symptoms should frost damage occur again.

Darren Camm, CCA, PAg, works for Richardson Pioneer Ltd. in Saskatoon, Sask.

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