Growers often wonder whether to swath right away after a light frost of minus 1°C or minus 2°C for a couple hours. Before doing anything, wait a day or two then assess frost damage.
—Light damage may cause some seeds to turn “shoe polish” brown, but pods and most seeds generally remain intact and turgid. (The photo below shows light frost damage.) With light damage in portions or throughout the field, leave the crop and swath at the proper stage based on seed colour change of the healthy seed. Swathing immediately after a light frost may result in higher economic and yield losses than if the crop were left alone.
—With moderate damage, pods will have white speckling on the outside and some seeds will turn brown and shrivel. However, pods remain reasonably intact and pliable and some seed remains green and turgid. Swath fields with light to moderate damage at 50% to 60% seed colour change, giving healthy seed time to reach optimum yield and quality. Damaged seed will shrivel and blow out of the combine with the chaff or end up as dockage. The key with moderate frost damage is to monitor the crop more closely than with other frost damage. If pods desiccate, they are prone to shattering, so consider swathing the whole field or just the affected areas if shattering losses could exceed gains from leaving the crop an extra day or two.
For more tips on what to do after frost, including tips for severe frost, click here to download the Canola Council of Canada factsheet, “Early fall frost. Now what?”