Crop advisor casebook: Did cutworms carve off these 80 acres of canola?

A Crop Advisor's Solution from the August 25, 2020 issue of Grainews

Rose Boughton.
photo: Supplied

Trent is a grain farmer in Wroxton, Sask., who called me last year in early July to tell me about an unusual problem — the canola in one of his fields was, quite literally, starting to disappear.

“I’m missing a whole bunch of plants here,” he said. “Last week the crop looked great, and this week I’m missing quite a few acres.”

Trent was convinced the large bare patches he was seeing in his canola field was the work of cutworms, even though there didn’t appear to be any signs of insect feeding. I didn’t know offhand what could be causing the problem but I was intrigued, so I told Trent I’d come out to his farm to have a look.

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When I showed up at the field, the barren patches were clear to see, and they were much larger than I expected. These areas, which contained no canola plants at all, were a sharp contrast to the rest of the crop, which looked excellent despite getting off to a late start due to a lack of rain earlier in the season.

Trent informed me the field had been in pasture prior to being planted with canola, and as a result of the drought conditions and a less than ideal seedbed, crop emergence had been spotty at first.

I had arrived at Trent’s farm bright and early at 7 a.m., which is one of the best times to scout for cutworms since they hate the hot sun. It didn’t take long for me to determine it wasn’t a cutworm problem.

In cases of severe cutworm infestation, you’ll usually find lots of worms working their way out of the soil as they search for more food; after an hour of digging around in the bare patches and around their outer edges, however, I turned up only two worms. I couldn’t find any dead, cut-down plants that are typical of cutworm damage anywhere either.

After I broke the news to Trent, he informed me about an issue he’d had with his seeder while planting the field that spring, and he wondered whether poor seed placement or seedling burn through overapplication of fertilizer could be a contributing factor.

The areas where Trent had experienced drill trouble, however, didn’t correspond with the bare patches in the field. Hilltops are the most likely places for seedling burn to show up since they typically have lighter soils, however, a hilltop right by one of the bare spots had a perfect plant stand, ruling out fertilizer toxicity as a possible cause.

At this point, the grower was getting increasingly anxious to know exactly what was going on, and justifiably so — Trent estimated he’d already lost 80 acres of his crop and he certainly didn’t want to lose any more.

Fortunately, I had seen enough to provide Trent with the answer he was looking for.

Crop Advisor’s Solution: Gophers responsible for missing canola

What I did find, however, were lots and lots of gopher holes. The rodents kept popping their heads out as I walked the field, so it wasn’t long before I became convinced gophers had to be the culprits.

I have seen five acres of a crop lost to gophers before, but never 80, so I knew this was a severe infestation. Within the bare patches, I couldn’t see any plants that had been chewed on or nibbled at — they were simply gone.

I never imagined gophers could eat so much in so little time; however, it appeared the combination of a dry year and fast-breaking soil in the field, which had previously been in pasture, allowed the furry pests to flourish.

After it was confirmed the crop was lost due to wildlife damage, Trent took steps to reduce the gopher population in the field after discussing control options with rural municipality officials.

As for his canola crop, the barren patches remained. In the end, Trent ended up with an excellent yield for the canola crop that remained in the field.

Gopher infestations like the one on Trent’s farm are very hard to anticipate, especially with unfamiliar land. They’re also not easy to correct in a single year.

Because of that, I let Trent know he should keep a close eye on the field for the next few years, particularly those areas that had sustained the most damage. That way, he could respond right away at the first sign of trouble to avoid having his valuable crops gobbled up by gophers.

Rose Boughton, CCA, ATAg, works for Richardson Pioneer Ltd. in Kamsack, Sask.

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