Spring and Winter Canola: Planting and Crop Development

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Pub 811: Agronomy Guide > Spring and Winter Canola > Planting and Crop Development

Excerpt from Agronomy Guide for Field Crops
Order OMAFRA Publication 811: Agronomy Guide for Field Crops

• Seed Quality
• Seed Treatments
• Spring Canola Seeding Date
  • Table 6-1. Amount of Seed Required to Meet Target Seeding Rate
• Seeding Rate
• Seed Bulking
• Seeding Depth
• Seeding Conditions
• Packing
• Broadcast Seeding
• Replant Decisions
• Plant Development
  • Table 6-2. Approximate Growing Degree Days to Reach Various Stages of Development
• Principal Growth Stages of Canola
  • Table 6-3. Nitrogen Recommendatons for Spring Canola
    

1. Seed Quality

Know the quality of the seed being planted. Germination is the major quality consideration used in grading seedlots. Germination standards test the ability of a seedlot to produce normal seedlings under favourable conditions of 95%-100% humidity and 25°C. Stress conditions in the field following planting often reduce field emergence compared to lab results. Certified seed must meet purity and germination standards.

Seed Treatments

Certified seed is treated with a fungicide and insecticide. The fungicide controls seed-borne and early-season soil-borne diseases, including blackleg, seed decay, damping-off and seedling blight. Insecticide seed treatments contol flea beetles for 2-4 weeks. Slow seedling development may allow flea beetle populations to build after the effectiveness of the seed treatement has declined, requiring a follow-up foliar insecticide treatment (see OMAFRA Publication 812, Field Crop Protection Guide).

Spring Canola Seeding Date

Typically, early seeding produces the highest yields. In recent years, some growers report good yields from seeding in mid-May. Consider, though, that flowering generally begins 50-55 days after planting and lasts 10-21 days. Temperature stress (>28°C) during flowering has a greater negative impact on yield than weather at any other stage.

Early Seeding

Seed as early as soil conditions permit. Canola will germinate and grow at a soil temperatures of 1°C, but 10°C is ideal for rapid emergence. Soil conditions and weather forecasts should be the ultimate guide, however 3°C or higher is a reasonable target for planting. Increase seeding rates by 5%-10% when canola is planted very early to account for slower emergence and increased seedling mortality. Canola is slower to establish than cereal crops and is less tolerant to spring frost. When seedlings emerge, the growing point is exposed between the cotyledon (seed) leaves and can be easily killed by a frost. Early planted canola also has a higher risk of infestation by cabbage seedpod weevil during the flowering/early pod stage. If canola growth is slow following planting due to cold weather, flea beatles may become a problem.

Late Seeding

If seeding is delayed, it is critical to conserve soil moisture and to plant into moisture for rapid, uniform emergence. Avoid seeding after June 1st in areas where swede midge has been identified. See Swede midge or visit the OMAFRA website at www.ontario.ca/crops.

Winter Canola Seeding Date

Seed winter canola August 15-30 (in Southwestern Ontario, August 20-September 10). Seeding within these dates results in the canola developing 4-6 leaves and an adequate size root system (approximately 1 1/4 cm or 1/2 in. diameter) to reduce the chances of frost heaving and desiccation in the spring. Delays beyond these dates greatly increase the risk of winterkill. If canola bolts in the fall, it will not survive through winter. Heavy competition from weeds or volunteer cereals in the fall can force canola growth, increasing chances of winterkill.

Seeding Rate

The optimum plant stand for canola is 75-130 plants/m² (7-12 plants/ft²). In 19-cm (7.5-in.) rows, this is equivalent to 14-25 plants/m (4.5-7.5 plants/ft) of row. Target seeding rates need to account for large differences in seed size between varieties. Table 6-1, Amount of Seed Required to Meet Target Seeding Rate, presents the desired seeding rate for different seed sizes. Increase seeding rates slightly (5%-10%) on soils prone to crusting, when seeding very early or very late.

Seed Bulking

Achieving target canola seeding rates can be a challenge with some drills. Calibrate seeding equipment before heading to the field. Ensure that each of the drill's seed cup openings are set the same. Bulking of seed with pelletized MAP (11-52-0), sulphur or corn cob grits are options for improving seeding rate accuracy. Do not use other fertilizers with canola seed, as this increases the risk of reduced seed germination.

Seeding Depth

Canola seedlings expend a great deal of energy to emerge, making quick, even emergence the goal in seeding. Seed 1.25-2.5 cm (1/2-1 in.) deep, if there is adequate moisture, and deeper if necessary to plant 0.6 cm (1/4 in.) into moisture, but not deeper than 4 cm (1 1/2 in.). If the depth to reach moisture is deeper, it is better to wait for moisture. Press wheels on the drill help place the seed uniformly at the bottom of the seed trench. Drill bounce is more of a problem at speeds over 8 km/hr. Increasing speed affects planting depth. If canola is seeded through the grass seed box, seed tubes should be directed behind openers and in front of the press wheels.

Seeding Rate

The seeding rate can be determined by knowing the 1,000-seed weight in grams found on the seed tag and using the following formula:

Metric

Seeding rate (kg/ha) = (desired plant population/m² x 1,000-seed wt. (gm) ÷ seedling survival rate) ÷ 100

Imperial

Seeding rate (lb/acre) = (desired plant population/ft² x 1,000-seed wt. ÷ seedling survival rate) ÷ 10.4


Seedling survival (final stand) = % germination (on seed tag) x % expected emergence

Sample Calculation

Using seed size of 5 gm/1,000 seeds, 72% final stand

Seeding Rate (lb/acre)

= (7 plants/ft² x 5 gm/1,000 ÷ 0.72) ÷ 10.4

= 4.7 lb/acre

Seed Drill Calibration

Collect and weigh (in grams) the seed from a drill opener and use the following formula to convert to lb of seed/acre using a 7.5 in. row width. Check several openers.

Seeding rate (lb/acre) = gm of seed/opener/30.5 m (100 ft) of travel x 1.54

Seeding Conditions

Good seedbed preparation is vital, due to canola's small seed size and shallow planting depth requirements. The seedbed should be level, firm, and crumbly with moisture in the top 2.5 cm (1 in.) of the surface. A crumbly soil will resist crusting after pounding rains, allowing the tiny seedlings to emerge. This is critical, since there is no opportunity to correct crusting. The crust can break the hypocotyl arch (the seedling stem) that lifts the cotyledons (seed leaves) above the soil surface. A firm seedbed will help hold moisture near the surface and aid in uniform planting depth and uniform emergence.

Packing

Let soil conditions determine whether to pack the seedbed before or after seeding. Packing before seeding can help level and firm the seedbed, improving seeding depth control and reducing soil moisture loss. Packing after planting can improve emergence and yield, if the soil dries out before emergence. Packing after seeding may bury the seed deeper if the field was ridged at seeding, thereby reducing emergence.

Broadcast Seeding

Broadcasting of canola seed is a greater risk than seeding with a drill but can still be effective in some situations. Some growers broadcast canola seed with fertilizer onto a prepared seedbed. The advantages of broadcast seeding are higher yield potential because of early seeding date, time savings and low cost. The major disadvantage of broadcast seeding is uneven planting depth and uneven seed application (if uncalibrated). Frost injury is also a risk with an early seeding date. Good seedbed preparation before broadcasting followed by harrowing or packing will keep seed depth constant and ensure good seed-to-soil contact. Despite this, broadcast stands can be inconsistent in dry years. Seeding rates should be higher when broadcast compared to drilled (6-8 kg/ha or 5-7 lb/acre).

Replant Decisions

Generally, canola plants in thin stands will branch out aggressively to compensate, resulting in no significant yield loss. Each year, some fields suffer from thin stands due to poor emergence, frost, insects and diseases. To make a decision, 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. A uniform stand of 11-22 healthy plants/m² (1-2 plants/ft²) will have a yield that is 90% of a full stand. Assess populations using the hula hoop method to determine plant populations (see Appendix K, Hula Hoop Method for Determining Plant and Pest Populations, on page 268).

Plant Development

Spring canola is a cool-season crop that grows best at temperatures above 10°C and below 30°C (optimum 20°C - 25°C). Crop development is closely related to the amount of sunshine received, although temperature also is a factor.

¹Adapted using research data from AAFC, Scott and Swift Current.
²Occurs when seed begins to mature, 10% seed colour change.

Development of canola is more closely aligned with growing degree days than crop heat units, similar to that of spring wheat. Canola matures in approximately 90-100 days in southern growing areas, and 110-120 days at New Liskeard. In northern growing regions, longer day length can partly compensate for lower temperatures. Drought and heat stress will shorten the days to reach maturity. The approximate GDDs to reach various stages of development is presented in Table 6-2, Approximate Growing Degree Days to Reach Various Stages of Development. High temperatures at flowering cause flower and pod abortion. Maturity differences among varieties is typically less than 7 days.

Principal Growth Stages of Canola

Rosette

Germination of canola is similar to other dicots - seedlings emerge with the growing point contained between cotyledons (seed leaves). A 5-6-leaf rosette forms, with larger, older leaves at the base and smaller, younger leaves developing in the centre. Leaf area development is directly related to growth rate and final yield.

Stem Elongation (Bolting)

Lengthening days and rising temperatures trigger bud formation in the centre of the rosette and the stem rapidly "bolts". The main stem reaches 30%-60% of its final height at the start of flowering. A large leaf area (especially upper leaves) at this stage strongly influences pod set and final yield.

Flower

Flowering begins with the opening of the lowest bud on the main stem and continues upward on both main and secondary branches. Flowering continues for about 14-21 days.

100 kg/ha = 90 lb/acre

To use this table, the price of canola must be known or estimated. Canola at $450/t and nitrogen at $1.50/kg results in a price ratio of 3.3 (1.50/0.45). At these prices, use 90 kg/ha of nitrogen.

Fertilization occurs within 24 hours of pollination. The maximum plant height is reached at peak flowering. Typically, flowering begins 50-55 days after planting (582-666 GDD). Temperature stress (>28°C) during flowering causes flower abortion and is detrimental to yield at this stage (Plate 33). Canola can either self-pollinate or cross-pollinate, depending on various environmental factors.

Plate 33. Heat blast. Hot temperatures during flowering (especially spring varieties) can cause heat blast and reduce seed yields.

Ripening

The leaf, stem and especially pod surface area are major food sources for the developing seed. Seed filling is complete about 30-40 days after flower opening. Pod ripening occurs from bottom to top of the plant. When seeds have turned green, leaf senescence begins, and the pod wall becomes the major source of food, although the stem is also important. When 30%-40% of seeds on a plant have started to change colour, seed at the top of plant will be nearly mature, and the average seed moisture will be 30%-35%.