There are some clear advantages to seeding canola early, including high yield and mitigating pest issues. This spring, ensure that your planting equipment is ready to go early in the season and get your canola crop off to a quick start.
Ideal planting dates in Ontario are typically in late April and early May. Germination can occur at soil temperatures as low as 1 or 2° C, but emergence will be more rapid at higher temperatures. Data posted by Canola Council of Canada suggests that if temperatures stay at 3°C it may take up to 14 days before full germination is achieved. At 6° C it will take only 8 days. However, beginning seeding at 3 or 4° C soil temperature is a reasonable target if soil conditions are fit for planting and temperatures are expected to rise. Even though soil conditions may be cool, early seeding will typically result in higher yields as long as adequate plant stands are established.
Soil conditions are, of course, of primary importance. Good soil moisture in the seed zone and adequate seed-to-soil contact are important for emergence. Residue should be evenly distributed and a firm seed bed will improve seed placement. With late seeding there may not be adequate moisture to seed at the recommended 1/2” to 1” depth, and deeper seeding will reduce emergence rates.
Spring frost can be an issue because the growing point is above ground and exposed between the cotyledons (seed leaves). However, a light frost may be tolerated, particularly if canola has reached the 3-4 leaf stage. If plants have “hardened” over several days of cold weather, they may be more tolerant of frost than rapidly growing plants. On the other hand, seeding late in May can lead to flowering during hot weather in late June and July and this temperature stress can have a huge impact on yield.
Good stand establishment and rapid, early growth is ideal for mitigating issues caused by insect pests. Flea beetle emergence from overwintering sites will peak at soil temperatures of 15° C, and it may take up to 3 weeks for all adults to emerge. Insecticide seed treatments control flea beetle for about 3 to 4 weeks, but slow early growth can mean that protection is lost before canola has passed out of the susceptible growth stage. At the 3-4 leaf stage, canola is often better able to outgrow the feeding damage.
Rapid, early growth is also ideal where swede midge is a concern. Swede midge adults emerge from the soil in mid-May to early June and larvae feed on the growing point at the center of the plant. A crop that bolts early may escape significant damage, and risk of swede midge damage is not a concern after flowering is initiated on secondary branches. Canola planted in late May or early June in areas with a history of swede midge faces high risk of damage.
Consider what the ideal seeding rate is for the given conditions. In an average year, somewhere between 40 and 60% of planted seeds will emerge. The ideal plant population is 7-13 plants/ft2 or 4.5-6 plants per foot of row on 7.5” rows. The benefits to having an adequately dense stand include increased light capture, mitigating losses to insect pests, and less branching leading to earlier and more even maturity. Your seeding rate should factor in the seed size, compensate for low emergence rates, and provide a final stand well within the ideal population for the best final yield results. Note that at a seed size of 4.75 g and seeding rate of 5 lb/ac, a typical 60% emergence rate will result in around just 4 plants per foot of row which is slightly below the ideal population. For very early or very late plantings the seeding rate should be bumped up by 5 to 10% to compensate for lower emergence rates.
A uniform stand will likely yield more than a non-uniform stand, even at the same plant population. In uneven stands the plants will compete for soil and light resources, and will branch more in thin areas, causing delayed and uneven maturity. After the crop emerges, determine the plant population and percent emergence, and note the uniformity of the crop. If there is a regular pattern across the field, uniformity may be affected by issues with your planting equipment. Take notes so you can make further improvements next year.