Canola Watch ALERT: Frost hits – should I swath?

September 4, 2018

Canola Watch Alert

Frost hits canola. Do I swath?

This is the question for many canola growers today as frost (in some areas heavy and long-lasting) hit parts of Alberta over night.

Start with these steps:

  • Check standing canola the morning after a frost.
  • Before taking any action, wait 4-6 hours after frost to allow the full extent of frost damage to become evident. The crop may look undamaged in the morning but by the afternoon wilting, desiccation and pod splitting may begin. This crop may need to be swathed to preserve yield, but keep in mind that high green counts are likely.
  • Light to moderate frost damage may take longer to show up. If no damage is evident after the first day and you decide to leave the crop to mature more fully, scout again after 2-3 days to reassess.
  • If most or all seed is mature and you planned to swath the day after a frost anyway, then don’t bother waiting 4-6 hours. Just start swathing.

Responses for heavy or light frost

Heavy frost… below -2°C: Assess the damage in early afternoon. Check pods for a white, wilted appearance. Pod shatter and pod drop could begin within a day, especially with warm sunny afternoons. If pods are desiccating rapidly, swathing right away will preserve as much yield as possible.

For canola with high seed moisture, frost in excess of -5°C is generally lethal, resulting in non-viable seed. At such low temperatures, ice crystals physically disrupt structures such as membranes and enzymes. Pods of immature canola crops frozen at lethal temperatures have been observed to turn black, whereas mild frost turns pods white or white-speckled.

Light frost… above -2°C: Hold off swathing. Check in the afternoon for wilting to make sure frost damage was not heavier than expected. You may see some speckling on the stem and pods, but this is of little concern as long as the plant is still alive. If no wilting, leave the crop standing and check daily.

What to look for during daily monitoring:

  • If the majority of the seeds remain green and immature, delay swathing to allow for further seed maturity.
  • If the pods are severely damaged and are beginning to desiccate, swath during periods of dew or high humidity to reduce the amount of pod shelling and pod drop.

Frost and quality. A killing frost will reduce quality, but that can’t be helped — whether you swath today or wait. Immature seeds (moisture content higher than 20%) will be damaged. Seeds with less than 20% moisture will normally escape damage. Green seed is the major downgrade that results from frost.

Got unanswered questions? Ask the Crop Production Team

More articles on canolawatch.org

More harvest frost scenarios to consider
Temperature is not always a good indicator of frost damage. Some crops seem to make it through fairly low temperatures in decent shape while others can have surprisingly high amounts of damage from a light frost. READ MORE

Frost in the forecast. Should I swath now?
The answer depends on (at least) two things: (1) How far advanced is the crop? (2) How cold will it get? READ MORE

Frost on canola left for straight combining
Frost provides some natural desiccation that may help dry weeds and green stems in fields left for straight combining. Some growers actually wait for frost before combining, using it as a tool to aid in crop dry down. READ MORE


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