Crop advisor casebook: The case of the desiccated canola

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

Melanie Sopatyk.
photo: Supplied

Matt is a grain farmer who grows 7,500 acres of wheat, malt barley, oats and canola at his place near Whitewood, Sask. He was out walking in his canola fields one day in early June when he came across some patches of withered, desiccated canola seedlings that fell apart as soon as they were touched.

The next day, Matt was alarmed to see even more disintegrating seedlings appearing in his canola fields, so he didn’t waste any time in giving me a call.

“I’ve never seen damage like this before,” he said. “The plants looked normal just a few days ago.”

I agreed to drive out to Matt’s farm to have a look for myself. Surveying one of the canola fields, it was evident that plant emergence was an issue. In some parts of the field, mostly in the higher areas, the seedlings were clearly lagging behind, and in other areas, there didn’t appear to be any canola plants growing at all.

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When I inspected the bare spots, I found lots of seeds that had germinated but failed to emerge from the soil. I could also see that in some places, the plants had managed to emerge but only their stems remained above the ground.

The canola that had emerged was at the cotyledon stage, and a closer look at some of the seedlings revealed tiny pinholes on the nascent seed leaves. I dug up some seedlings to have a look at their roots, but the root systems all appeared to be robust and healthy.

I considered whether fertilizer burn could be the culprit, but I ruled that out when Matt informed me side banding was the application method he’d used to fertilize his canola. I also eliminated residual herbicide injury as a possibility, since I knew Matt didn’t utilize any residual herbicides in his rotation. In addition, I was aware that Matt had applied glyphosate to his canola fields prior to planting, but his burnoff hadn’t included any other herbicides that could have damaged the emerging crop.

It had been a poor start to the growing season, with a late frost near the end of May that was closely followed by a couple of days of very hot and windy conditions. As well, there had been very little rain to speak of that spring.

I suspected all of this had something to do with what I was seeing in Matt’s canola fields, but I also had a pretty good idea that weather was only part of the answer.

Crop advisor’s solution: Poor weather and flea beetles responsible for ailing canola crop

After eliminating fertilizer burn and residual herbicide injury as possible causes, I considered whether some kind of root rot was responsible for the ailing canola seedlings, which were at the cotyledon stage. That was quickly ruled out when I found the roots of some affected plants I’d dug up all appeared to be healthy and robust.

I also saw many canola seedlings had tiny pinprick holes on their nascent seed leaves — the kind of damage typically caused by flea beetles. After examining plants in other areas of the field, it was evident there had been widespread flea beetle feeding, causing defoliation that by my estimation ranged from five per cent all the way up to 75 per cent of affected seedlings.

When I considered recent weather conditions, however, I knew blame for the generally poor state of Matt’s canola didn’t just lie with the flea beetles. For a start, cool, dry conditions early on had likely prevented or delayed canola germination and emergence, which accounted for the bare spots and ungerminated seeds I’d observed in many areas of the field.

Any plants that had emerged would’ve been damaged by a late frost at the end of May and then dried out by extreme heat and windy conditions that occurred a few days after that. All this environmental stress would have constrained vegetative growth, and it was clear that in many areas, ravaging flea beetles had made a feast of seedling tissues that were above ground.

There had also been next to no rain all spring long, contributing to the widespread plant desiccation and also explaining why plant stands in the highest areas of the field were generally shorter and hardest hit by drought stress.

I let the grower know that it was the weather, in combination with high flea beetle pressure, that was responsible for his ailing canola. I also informed Matt there wasn’t anything he could really do to salvage his canola crops and his best option was to reseed the fields, which he did.

To avoid a similar problem in the future, Matt would be wise to monitor the weather closely and, if he can, adjust his planting time accordingly. Freshly seeded canola does best in warm, moist soils, and the quicker a crop can germinate and emerge, the better chance it has to get ahead of insects as well as weeds.

It’s also a good idea to scout frequently and regularly as canola emerges, especially in challenging weather conditions, to check on the state of the crop and to determine if flea beetles could pose a threat.

Overwintering flea beetle populations will start to emerge with the first extended warm period in April or May, and when conditions are right, they can quickly infest a canola field if left unchecked. For this reason, it’s a good practice for canola growers to keep a close eye out for the insects throughout the growing season so they can take the necessary steps to control the pests once economic thresholds are met.

Melanie Sopatyk, CCA, AAg, works for Richardson Pioneer Ltd. in Whitewood, Sask.

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