Canola School: Resolving the re-seeding decision

The decision to re-seed a canola crop can be a difficult one, and the reasons to re-seed can be numerous: wind damage or sandblasting, especially in sandier soils, insect damage from cutworms or flea beetles, or overall low plant density.

In this episode of RealAgriculture’s Canola School, Kara Oosterhuis chats re-seeding decisions with Autumn Barnes, an agronomy specialist with the Canola Council of Canada, based at Lethbridge, Alta. (Story continues below video)

Significant winds across the Prairies can really beat up canola in the early cotyledon stages, especially if the soil is sandy, resulting in sandblasting. Weeds can also get battered, which causes herbicide efficacy concerns, as there’s less leaf area as a target for spraying.

Insect damage is also a concern, flea beetles and cutworms can wreak havoc. Heavy rains can cause crusting, making it harder for seedlings to successfully emerge. So how should you decide if you need to re-seed your canola or not?

Barnes says, “It’s about getting out, putting boots in your field, getting out of your truck, getting away from the headlands and away from the entrances and getting a good picture of what the field looks like.” Her favourite tool for scouting canola early on is a hula hoop, as it can be easily thrown and gets a true representative sample of the field.

With frost, you’ll need to wait a few days to see if the canola will bounce back. Frost damage can look brutal, but sometimes the canola will pull through.

Plant density is really important when considering re-seeding. “We recommend five to eight plants per square foot, as a plant density for canola,” says Barnes.

Yield predictability and stability declines around the three to four plants per square foot measure. “It doesn’t mean you’ll have a disaster in the fall if you have fewer plants than that, it just means the predictability decreases, and you’re more likely to get a lower yield,” advises Barnes.

It gets difficult to make that re-seed decision when plant density is down to one to two plants per square foot. “If you have big patches of no plants at all, perhaps you can just reseed those patches. If you have smaller patches of no plants at all, is the rest of the field going to be able to compensate?” says Barnes. One to two plants per square foot can often fare better than a crop that’s re-seeded in mid-June.

When you’re going out and doing these plant density assessments, the plant density count should be done at the two to four leaf stage — cotyledons are an indicator that not all the plants have come up yet. Make sure you’re not counting volunteers in that number. When looking at emergence, consider any plants that have started, but haven’t emerged out of the ground. (Side note: be sure to diagnose why there’s poor emergence).

When is it too late to re-seed, you may be asking? Especially in southern Alta., hotter weather during July can cause significant pod-abortion and flower blasting. The later you seed, the more susceptible your crop is to these conditions.

Ideally, canola is seeded the first week of May in southern Alberta. Into early June, the economic pros and cons should be weighed. It’ll be a balance of managing weeds and a potentially uneven canola crop throughout the season or you may end up re-seeding to a different crop, which may mean a different dollar value in your pocket in the end. The field’s herbicide history may factor into that decision.

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