Don’t rush to reseed frosted canola acres: CCC

Warm temperatures continue to be elusive for canola growers across much of the Prairies, as many areas continue to experience below-average daytime and nighttime temperatures.

In Manitoba alone, the Canola Council of Canada reports, growing degree days (GDD) to date range between 40 to 60 per cent of normal and as a result, emergence, growth and development are also lagging.

Emergence is not only slow but in some fields, uneven. Research has shown much lower and slower canola germination at low temperatures, the council noted.

Soil temperatures above 5°C have little effect on the time to 50 per cent germination; however, the number of days to 50 per cent germination increases dramatically at temperatures below 4°C (with germination taking as long as nine days at 3°C or over 12 days at 2°C).

Now is the time to get down and scout to find out what’s happening beneath the soil surface, the council urged. If emergence is patchy, dig around looking for the reason. Is an insect (cutworms, wireworms) interfering? Is it too dry and the seed is still intact? Is the white, healthy hypocotyl making its way through the soil to the surface, albeit slowly?


Canola seeding is virtually complete in Alberta and Saskatchewan, the council said, but where soil moisture is adequate for germination, cool temperatures and late-spring frosts are stalling canola growth and development. Emerged fields range from the cotyledon to two- or three-leaf stage.

Where conditions are dry (south and west-central Saskatchewan, southeast-central Alberta), some canola is stranded in dry soil and will require rainfall to stimulate germination.

In Manitoba, meanwhile, seeding is ongoing in parts of the northwest and central regions. About 30 per cent of the early-seeded canola has emerged in these regions. Seeding is nearing completion in the southwest and about 50 per cent of the canola has emerged.

Excess moisture, however, continues to challenge producers in the eastern and Interlake regions. Seeding varies from five to 100 per cent complete and has been focused on fields that will support equipment and the crops with the earliest seeding deadlines (such as June 1 for soybeans) rather than the typical seeding sequence. There are reports of broadcast seeding of canola in Manitoba’s southeast and Interlake.

Patience after frost

Frost was widespread Tuesday morning all across Western Canada, the council noted. Overnight lows were recorded in the neighborhood of 0°C to -2°C with some areas reporting -3°C.

Temperatures in this range are usually labeled a “light frost” and significant crop damage is not expected, but many variables will affect a crop’s ability to withstand frost (duration of the frost, crop staging, crop residue, low-lying areas, crop vigor and so on), so the only way to assess the extent of frost damage is to get out and scout, the council said.

Symptoms of frost will often be noticed within hours, but plant survival cannot be confirmed for several days. Plant material will be wilted and discolored (whitening, yellowing). More severe damage will cause necrosis (browning or blackening) of cotyledons and leaves.

Light frosts are often not lethal to the growing point (top, centre of the stem). This is where all new growth is initiated so if it is still green, the plant can re-grow from this point, the council said.

Therefore, the council advised growers to resist the urge to re-seed immediately after this frost, as recovery may turn out better than expected. Wait at least three to four days to determine if the growing point is still intact and new green growth is visible. The frost may thin the stand only, especially in low-lying areas.

As a guide, a reasonable plant population early in the season is three to four plants per square foot. However, one to two plants per square foot across the majority of a field can be adequate if managed carefully with today’s herbicide-tolerant systems, the council said.

Thin stands such as these can yield up to 90 per cent of a normal stand seeded at an early date but will be later in maturity. Crops reseeded late in the season typically yield less than earlier-seeded crops that had thin stands, the council warns.

For example, one council case study showed a 7.4 bushel per acre advantage when a crop was not reseeded after a frost. It likely will be better to leave a thinner stand, provided it is reasonably uniform, than take the risk of late re-seeding because maturity/early fall frost becomes a concern.

When deciding whether to reseed or seed late, assess the maturity of the chosen variety, the council said. It may be getting too late to plant longer-season varieties based on the frost-free period remaining. If necessary, ask a local retailer to suggest other suitable varieties for the area.

Also, keep crop insurance deadlines in mind, the council said. The crop insurance seeding deadline for Saskatchewan is June 20. In Alberta, deadlines are May 31 for full coverage and June 20 for limited coverage. Manitoba Agricultural Services Corp., meanwhile, has indicated that no extensions to seeding deadlines will be announced.

Broadcasting tips, if needed

The continued delay in seeding progress due to wet weather in Manitoba has led to many questions regarding the feasibility of broadcast seeding, the council noted. In general, broadcast seeding is not recommended, because it usually results in lower yields compared to drill seeding.

But producers faced with wet conditions that limit equipment flotation, coupled with the risk of fall frost, may wish to consider broadcast seeding in order to plant their seed in a more timely fashion.

Farmers who try broadcasting canola should increase seeding rates slightly to compensate for non-uniform seed depth. Consider lightly cultivating (two to four centimetres) or harrowing to incorporate the seed into the soil if field conditions allow. However, avoid creating lumps or clods during cultivation or straw piles with harrows or cultivators.

If broadcasting fertilizer as well as seed, the council said, be aware that broadcast phosphorus is only about half as efficient as banded phosphorous. There also can be greater risk of denitrification on saturated soils, reducing nitrogen fertilizer efficiency. Adjust fertilizer rates accordingly, the council said, keeping in mind a realistic target yield based on the time of year and field conditions.

And if broadcasting seed by aircraft, the council advised, make sure the seed doesn’t get “blasted” into the ground too deeply, making emergence slow and difficult.

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