Spring and Winter Canola: Other Crop Problems

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| Insects and Pests of Field Crops | Diseases of Field Crops | Appendices |

Pub 811: Agronomy Guide > Spring and Winter Canola > Other Crop Problems

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

• Insects and Diseases
• Frost
• Hail Damage
  • Table 6-6. Percentage Yield Loss Due to the Destruction of Branches During Flowering in Canola
• Brown-Seed (Heat Damaged)
• Green Seed Problems
• Winterkill
• Cross-Pollination

Insects and Diseases

Figure 6-1, Canola Scouting Calendar, shows insects and diseases that could be causing symptoms in the field. Individual descriptions of insects and diseases, scouting and management strategies can be found in Chapter 13, Insects and Pests of Field Crops, and Chapter 14, Diseases of Field Crops.

Recommended treatments to control insects, pests and diseases can be found in OMAFRA Publication 812, Field Crop Protection Guide.

Frost

Canola seedlings can recover from a light spring frost if the growing point is not damaged. Prior to taking any action, wait 4-5 days to assess damage. Check the growing point for green colour at the centre of the leaf rosettes (Plate 31). Although the cotyledons or other leaves may be black, re-growth can occur in 4-10 days, depending on weather conditions.

Plate 31. Canola seedings can recover from frost if the growing point is not damaged. The growing point will remain green.

Seedlings are more tolerant of frost at the 3-4-leaf stage than at the cotyledon stage. Ice crystals can form on the surface of plants without necessarily causing serious damage. Water within plant cells contains dissolved products that lower the freezing point by several degrees over water outside the cell. The length of time the plant is exposed to freezing temperatures is important, since a sharp frost that lasts only a short period may cause less damage than a mild frost that lasts all night. Rapidly growing plants are less tolerant of frost than plants that have undergone several days of cold weather (hardening).

Frost can be more damaging to canola that is in the flowering stage. Although pollination may not be affected, seeds that have begun to develop about a week prior to pollination will be affected by several hours at freezing temperatures (-3°C to -4°C). These freezing temperatures can also reduce seed fill. Check pods for damaged seeds that have lost their green colour and turgidity (Plate 32).

Plate 32. Cold temperatures leaf injury in winter canola.

Hail Damage

If hail removes both cotyledons or the stem is broken below the cotyledons, plants usually do not survive, but the yield impact will not be as large as the loss of plants. If hail occurs during vegetative growth, yield loss will be dependent on the amount of leaf area destroyed. Yield loss will equal approximately 25% of the leaf area destroyed. Stem bruising and breakage will result in higher losses.

Source: Canola Council of Canada, 1994.
Research conducted in Western Canada.

If hail occurs during flowering, plants can compensate by developing secondary clusters and new branches (see Table 6-6, Percentage Yield Loss Due to the Destruction of Branches During Flowering in Canola). Yield losses will be highest when hail occurs during late flowering and during pod fill. Canola has poor ability to recover from hail once the pod-fill stage is reached. Expect that hail between flowering and pod fill will result in uneven maturity as a result of a later flush of growth or flowers.

Brown-Seed (Heat Damaged)

Brown-seed has been an occasional problem in some years. Brown-seed refers to the brown internal colour of the seed when crushed and is caused by premature abortion of the developing cotyledons. Brown seeds are produced when canola is subjected to extended periods of high temperatures and moisture stress due to dry conditions, during pod fill. High levels of brown-seed may not be suitable for processing for the food market because of much higher free fatty acids (FFA) and phosphorus levels. High FFAs occur when the oil in the seed breaks down. This results in unstable oil that is subject to more rapid rancidity. There is limited research that suggsts that brown seed is increased by insect feeding on developing seeds by tarnished plant bug or lygus bug and cabbage seedpod weevil. Registration of new varieties requires the FFA levels to be lower than those of current varieties.

Green Seed Problems

Green seed is an important grade determinate with Grade #1 canola containing a maximum 2.0% green seed. Green (immature) seeds are distinctly green when crushed. Green seed occurs when chlorophyll becomes "locked in" the seed at harvest. Causes include:

• early frost
• swathing or direct harvesting too early
• uneven crop maturity
• variety
• hot, very low humidity during ripening

Natural plant enzymes break down chlorophyll as seeds mature. Air temperature and seed moisture is important in the breakdown of chlorophyll. When seed moisture drops below 20%, enzyme activity and seed respiration slows, reducing the rate at which green seed clears. Green seed that is stored at correct safe moisture levels (<10%) will not show any reduction in green seed content . A sub-lethal frost (about 0°C to -10°C) can slow and even reverse the enzyme activity that breaks down chlorophyll. The main effect of a frost is that it causes a rapid dry-down of pods and seeds before the chlorophyll has a chance to clear. Thin stands result in more branching of plants and an increase in variability in seed maturity.

Winterkill

Winter canola is less winter-hardy than winter wheat in Ontario. Winterkill is most common in March and April after winter canola loses its winterhardiness, begins to grow and then is damaged by a return to extremely cold temperatures. Winterkill can also result from a lack of winter snow cover, prolonged periods of ice cover and desiccation by winter winds, resulting in weakened stands.

Heaving is an issue where there is not sufficient snow cover into late March-April when freeze-thaw cycles cause heaving, particularly on poorly drained soils. Small plants that did not become adequately established lack the lateral roots necessary to anchor the plant against heaving. In saturated soils, freeze thaw cycles can damage the top portion of the taproot, allowing root rot to invade. Plants that heave by more than 4 cm (1.5 in.) often don't survive.

If the damage is severe enough (75% kill), the crop may not be salvageable. However, if 30% of the stand remains, with healthy plants evenly distributed across the field, the crop will compensate sufficiently.

Cross-Pollination

If varieties with different herbicide-resistant traits are allowed to cross-pollinate, the result may be volunteer plants with multiple resistance traits in subsequent crops. Separate fields planted to varieties resistant to different herbicides by a minimum of 175 m. This isolation will reduce the occurrence of field-to-field cross-pollination. Research at AAFC, Swift Current, has indicated that pollination contamination was 2.1% at 46 m (150 ft), 1.1% at 137 m (450 ft) and 0.6% at 366 m (1,200 ft).

A more recent study found that the first 100 m (330 ft) of an adjoining field contained about 99% of the unwanted pollen.