Rain and delayed harvest can cause cut canola plants to regrow in some cases. This regrowth coming up through swaths can make for increased green matter going through the combine. These high-green plants can reduce separator performance and increase wet green dockage in the sample, which increases the storage risk.
This regrowth cannot be sprayed. Once canola is cut, no product can be applied. Pre-harvest intervals are closed for all products, and spraying swaths mean residues will end up in or on the seed resulting in an increase risk of exceeding allowable test levels.
Spraying regrowth in the windrow wouldn’t work that well anyway. Herbicides need to make contact with what they are to control. With most of the target area buried in the swath, there would be an insufficient dose to control regrowing plants.
The only canola fields that can be sprayed are standing crops. Yet because they’re still standing, regrowth from cut stems will not happen. This could be seen as another factor in favour of straight cutting.