Assessing Canola Stands
The optimum plant stand is 202,000 to 344,000 plants/ac or 50 to 85 plants/m2 (5 to 8 plants/ft2). At the recommended seeding rate range of 80 to 120 seeds/m2 (320,000 to 485,000 seeds/ac), an emergence rate of approximately 60% will result in acceptable stands. Canola can yield strongly across a wide range of populations; a stand of 55 plants/m2 has the same yield potential as a stand of 215/m2 (20 plants/ft2). To evaluate the effectiveness of planting, check the field population about 3 weeks after planting.
To estimate the plant population of canola seeded on 19 cm (7.5 in.) row spacings, a square frame with a known area can be placed on the ground and plants counted within the frame. If the canola is seeded on 38 cm (15 in.) spacings count plants along 5.31 m (17 ft 5 in.) of row within 2 neighbouring rows and multiply by 1000 to determine plants/ac.
Generally, canola plants in thin stands will branch out aggressively to compensate, resulting in no significant yield loss. A stand of 20–40 healthy plants/m2 (2–4 plants/ft2) can produce a viable crop yielding about 90% of an optimum stand. A 90% yield potential is often better than re-seeding, which results in higher costs and late seeding. Uniformly thin stands will perform better than uneven stands. Thin stands may have a longer flowering period and mature later. Thin stands have a limited ability to buffer insect feeding damage and stand loss, such as significant flea beetle feeding. When moisture is limited, low density stands may not be able produce adequate yields.
Replant Decisions
When considering replant decisions, it is important to first assess the health and plant population of the surviving stand. It is easy to overestimate the extent of the injury and underestimate the ability of seedlings to recover. If plant populations are below 40 healthy plants/m2 (4 plants/ft2) prior to the 4-leaf stage, consider the percent of field affected, uniformity of the stand, soil moisture, weed pressure, flea beetle pressure, and the costs and calendar date of reseeding. Assess root health, remembering that seed fungicide treatments provide control of seedling blights for 2–3 weeks. Signs of poor root health include brown discoloration of taproot and pinching off of the plant stem near the soil surface.