One of the most common agronomic questions regarding canola is “When should I swath?” And the short answer is, “It depends.”
It depends on the circumstances of the crop and of the growing season in which the crop is maturing. Sometimes you see farmers, fearful of crop loss due to shattering, swathing canola that is as green as grass, with little or no seed colour change. Because canola is an elastic plant and also because flowering (and therefore seed maturation) takes place over a period of time, choosing the correct swath timing can sometimes be quite a challenge. There are several misconceptions regarding swath timing and its impact on green seed and shattering.
Green seed in canola occurs when the degreening enzymes, which are active under reasonable temperatures and seed moisture levels above 20 per cent, are unable to complete their job because of low temperatures and/or low seed moisture. Low seed moisture occurs when the crop dries down too quickly in hot and windy conditions or when seeds are desiccated due to frost destroying the cell walls in the seeds, which prevents them from holding moisture for further metabolic activity.
In this article, I’ll review the principles of swath timing for canola and when you should look at altering it to optimize crop quality and yield.
In general, under normal maturation and weather conditions, canola is ready for swathing when approximately 50 to 60 per cent of the seeds in the pods on the main stem have started to change colour (SCC). This colour change can be yellow, tan, brown or black (depending on the variety and weather conditions)
and just has to be seen on part of the seed, not cover the seed completely. Under these conditions, enough seeds will be physiologically mature to balance the concerns of shattering more mature seeds in the lower parts of the main stem to the less mature and greener seeds in the pods on the upper parts of the main stem.
You can delay swathing until about 70 per cent SCC, but any further delays may cause excessive pod shatter. Under normal conditions, you should not swath much before 50 per cent SCC, as yields will usually be lower due to smaller and/or lighter seeds. These recommendations were based largely on research conducted by Canola Council staff and published in their ‘Time of Swathing’ brochure which is available on-line at https:// canola-council. merchantsecure.com/canola_resources/product12.aspx. A useful video outlining how to go about assessing seed colour change is available online at: http://www.canolawatch.org/2011/05/03/how-to-determine- when-to-swath/.
SWATHING TO AVOID GREEN SEED
There are a few circumstances where when altering those general swathing recommendations can lower the amount of green seed.
The first is when conditions are hot, dry and windy, which causes the crop to dry down rapidly and doesn’t allow proper curing to take place. Under these conditions, you have the double whammy of lower yields because seeds have not filled completely plus the much greater risk of higher green seed. The rapid drying reduces moisture levels in the seed before completion of the proper degreening processes, which results in higher levels of green seed. Under these conditions, you should delay swathing as late as possible (until 70 per cent SCC if possible) and plan on swathing in the evening or through the night when temperatures are lower and humidity levels higher. If you do end up locking in the green seed due to cutting too soon, leaving the crop in the swath for longer periods for a possible rain to rehydrate the seeds can help. This re-wetting reactivates the degreening enzymes (which generally stop working below 20-per-cent moisture levels) and can help lower green seed levels.
SWATHING IN THE FACE OF FROST
A second such situation is when the crop is still greener than normal and a fall frost is imminent. Under these conditions, you can swath canola as early as 10 to 20 per cent SCC and lower the chances of green seed. In this case, swathing earlier allows the plant to dry down before the frost, which lowers the amount of free water in the seed and lowers the point at which the frost will cause damage. However, before deciding on cutting earlier to avoid green seed, you also need to consider the current weather and short-term forecast. To avoid chances of higher green seed, you usually need to swath at least three days or so before an imminent killing frost. Cutting any later will not generally allow enough seed drying to occur to significantly reduce the chances of frost damage. Cool and humid weather conditions will also extend the time required before frost damage occurs. So hearing a weather forecast for frost the following evening and jumping on the swather to knock down the canola the day before will usually not help.
So what should you do if you do get a frost on your canola before you have swathed it?
First, don’t be in a big rush to knock it down until the condition of the crop and the amount of damage can be assessed. With light to moderate damage (when the outside of the pods are speckled but the pods are intact and not in any danger of desiccating), then leaving the crop standing to continue maturation is the best course of action. Only when the frost severely damaged the outside of the pods and where rapid fluid loss from the outside of the pods is occurring, should you swath quickly in order to preserve as much crop volume as possible. Secondly, check the crop on a daily basis to assess the condition and further evaluate the frost damage. And thirdly, allow the crop to continue maturation as long as possible to allow the remaining seeds to continue as much degreening as possible before the remaining crop is at the appropriate stage for harvest. For more detailed information on how a fall frost impacts canola maturation get to the following factsheet on the Canola Council website at: https://canola- council.merchantsecure.com/canola_resources/product39.aspx.
Hopefully this article has explained the basic principles of seed colour change in canola, the optimum time for swathing, and when to considering altering that timing when weather conditions are less than average or “normal.”
JohnMaykoisasenioragri-coachwith Agri-TrendAgrologyandoffersagri-coaching servicesintheMundare,Alta.,areawherehe alsofarmswithhisfamily.
To avoid chances of higher green seed, you usually need to swath at least three days or so before an imminent killing frost