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When growers have canola stands of fewer than 4 plants per square foot — due to low seeding rates, poor seed survival, insects, crusting, frost, wind, etc. — they grapple with the question whether to reseed. An established canola stand with as few as 1-2 plants per square foot generally has higher economic potential than if growers were to reseed that crop. This population is far below the minimum 5 per square foot required to meet yield potential, but a thin stand seeded early has greater economic potential (considering yield, quality and cost of production) than an adequate stand that doesn’t get established until mid to late June.
But what if reseeding occurs in May instead of June? Yield potential for canola seeded in late May is not as high, generally, as canola seeded in early May, but it is still pretty good and better than for canola seeded in June. Given the current date, the argument in favour of reseeding a crop clearly thinned out and set back by frost or any other issue may have more merit.
Reseeding may be the better option if:
—The stand is 1-2 plants per square foot and not uniform. If large areas of the field have fewer than one plant per square foot, while some areas have 5-10, for example, this field will not likely have the same yield potential as a field with 1-2 plants, or more, spread evenly across the field. A uniform plant stand is crucial at low plant populations.
—Weeds are large and outnumber the crop and cannot be controlled effectively with in-crop sprays.
—Crop insurance will pay a reseed benefit and/or seed companies have reseeding rebates on seed. This helps with the economics, especially in May when a reseeded crop still has time to reach its yield potential.
—You can get a similar full-season hybrid. A 2010-12 study at Western Applied Research Corporation (WARC) in Scott, Saskatchewan, found that re-seeding to the same full-season variety in early June resulted in significantly higher yields at 50% of sites compared to the low plant population control (fewer than 4 plants per square foot) seeded in mid May. The study found that the chances of getting No. 1 grade are lower with canola reseeded in June in this situation, but higher yield potential and a crop insurance reseed benefit can make up for it about half the time. The WARC study also found that: (1) Re-seeding in early June to a slightly shorter season variety (9350RR) resulted in higher yields than the earlier-seeded low population control at only 25% of site years. (2) Reseeding to Polish canola did not pay.
—Final considerations in the reseed decision, as outlined in the study, are to look at the current and forecast moisture situation to make sure the reseeded crop can emerge quickly, and keep in mind that big plants from a thin stand may provide harvest challenges in terms of variability.
Further reading:
More reseeding considerations: The reseeding decison — new research