Staging canola for swathing or pre-harvest desiccation is critical to maintain high quality seed and maintain yield. Ideal swath timing is when 60% of seeds on the main stem have turned colour, meaning 60% of all the main stem seeds are showing some form of colour (yellow, brown, black) other than green.
For 60% seed colour change, the bottom third of the main stem of the plant will have totally brown/black to purplish seeds, the middle third will have turned, or be showing some spots of colour, and the top third are green. The green seeds must be firm and should roll between your fingers without squishing. At this stage, the average moisture content is about 30%.
Producers are reminded that more than one area in a field will need to be assessed for seed colour change. Relying on a visual assessment of canola pod colour alone will not provide an accurate estimate of crop stage. In many cases, the outside of the pod colour can turn brownish yellow but seeds inside may still be green.
Delaying swathing of canola until the 60% seed colour change stage usually allows for:
- Improved yield and quality through increased seed size
- Reducing green seed
- Higher oil content
- Minimizing economic shattering losses
Earlier swathing tends to lock in green chlorophyll in underdeveloped seeds, reducing oil content and potentially causing marketing issues. Canola can be swathed in the 30-40% seed colour change stage to manage a large number of acres ripening at the same time, but producers should be aware that swathing at this stage can cause yield losses up to 8%.
Dry growing conditions and damaging weather have impacted canola development across Manitoba in 2018. Evaluating canola fields for evenness and uniformity is important to selecting the right time to swath or desiccate the crop. If growth conditions allowed large patches of delayed emergence, or hail set back crop development, estimating the patch size and managing the crop according to the largest percentage area is a good recommended practice.
Glyphosate, Heat and Diquat herbicides are all registered for use as either a pre-harvest aid or a desiccant on canola. Check the labels or the Guide to Crop Protection (https://www.gov.mb.ca/agriculture/crops/guides-and-publications/#gfcp) to know their specific use.
In general, a pre-harvest aid (glyphosate and Heat LQ) should be used to increase plant tissue drydown and kill green weeds. The correct stage is 60-75% seed colour change. Expect to harvest the crop 1-3 weeks after spraying, similar to the time expected between swathing and harvesting.
A desiccant with the active ingredient diquat works more quickly, forcing removal of crop moisture. A fast-acting product, expect to harvest 4-7 days after application. Target a minimum of 90% seed colour change, as diquat will lock in any remaining green chlorophyll in the seed.
Points to Consider
Caution is advised when swathing or desiccating a canola crop, since that is considered growth and development termination, according to pre-harvest interval (PHI) standards. Know the length in days PHI of the fungicide and/or insecticide used on the crop; swathing or desiccating should not take place before that PHI window closes.
More tips on canola harvest management can be found here: https://www.canolacouncil.org/media/530966/canola_swathing_guide.pdf