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Freezing temperatures were again widespread last week and over the weekend in many parts of the prairies. This may prompt canola growers to consider reseeding. However, resist the urge to reseed immediately, as recovery may turn out to be better than expected, especially if seed has not yet germinated or the young seedlings have become acclimated to the cold. If the seed has not germinated and is still hard/firm, not soft/mushy, it will likely survive and just needs warmer conditions. After several days of near freezing temperatures, emerging canola that is near the surface or that emerged under cool conditions will undergo a gradual hardening process, allowing the plants to withstand freezing temperatures without serious damage. Studies have shown that early-seeded canola seedlings that had undergone hardening could withstand minus 8 to minus 12°C temperatures. Cooler conditions result in plants that are slower growing, producing smaller cells that have a higher concentration of soluble substances that make them more resistant to frost damage. This hardening off process helps defend plants against the chain of plant gene activities set off by cold weather that produce or degrade the proteins that protect plant cells. Wait at least three to five days or longer depending on growing conditions before making any decisions on canola crops. Remember there is no “minimum number of plants” because growing conditions can have a significant impact on the ability of the plant to compensate. As a guide, a reasonable threshold for conventional varieties is 3 to 4 plants/ft2 early in the season. However, with herbicide-tolerant systems, 1 to 2 plants//ft2 can be adequate with late-season seeding or reseeding. Thin stands such as these can yield up to 90% of the 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 that had poor stands. It will likely be better to leave a thinner stand (provided it is uniform) than take the risk of late reseeding because maturity/early fall frost becomes a concern.
For more information on assessing frost damage in canola see the following link: https://canola-council.merchantsecure.com/canola_resources/product37.aspx