Timing questions: Swathing and pre-harvest aids

Here are some timing considerations as harvest nears.

If swathing: Canola fields swathed at 60% seed colour change (SCC) on the main stem can yield 8% more than fields swathed at 30% SCC. That’s according to Canola Council of Canada research from the early 2000s. The yield difference could be even higher with lower plant populations because with fewer larger plants more of the yield will be in the side branches. Later swathing increases crop yield because side branches have longer to fill and average seed size for the whole plant is larger. The ideal is to swath when most (or all) side-branch seeds are “firm to roll.”

Tips on how to assess seed colour change.

If straight combining: The question is whether to let the crop dry down naturally (at this stage of harvest, we have time to wait) or to apply a pre-harvest spray. If leaning toward a spray, what is the goal with a pre-harvest application?

If weed control is the goal, assess the weed situation and crop stage before spraying glyphosate. It is critical to wait until seed moisture content is less than 30% in the least-mature areas of the crop before applying glyphosate. Applications made before the correct stage increase the risk of unacceptable residue in the seed. When making your assessment, here’s what to look for:

  • By waiting until 50 to 60% seed colour change in the least-mature areas of the field, growers can be confident seed moisture will be at less than 30%.
  • At this stage, seeds in the main stem will be green and firm to roll in the top third of the plant, mostly brown with some speckling in the middle third, and completely brown-black in the bottom third.

Once the crop is at that stage, assess the weed situation to see if a spray is warranted. Moderate to heavy infestations of annual or grassy weeds should be sprayed out. Perennial weeds could be left alone for a late fall application, which will likely provide better control.

If desiccation (crop and weed dry-down) is the goal for straight combining, this decision should wait until just before harvest – for two reasons. (1) With a lot of canola crops moving quickly toward maturity, harvest will not be as rushed and the crop should have lots of time to dry down naturally for straight combining. Desiccant spray may not be needed. (2) Diquat desiccant can’t be applied early anyway. Diquat application timing is 90% brown seed. At this stage, all but 10% of the seeds on the very top and outer most branches haven’t completely turned black or brown. See more timing tips for pre-harvest products.