Here are factors that create the ideal situation for straight combining canola:
Knitted crop. The crop should be well knitted and slightly lodged to reduce potential seed loss through pod shelling and drop. If a large proportion of the plants appear to move independently in the wind, they will be at higher risk for shattering loss as the plants senesce and dry down.
Pod integrity. If a lot of pods have been damaged by frost, drought, hail or insect damage, this may not be a good candidate field for straight combining. Hail will typically cause more damage to a standing crop than a swathed crop.
Uniform growth stage. A uniform crop with all plants drying down at the same rate makes straight combining easier to time.
Minimal green weed growth. Weeds may stay green longer, and make straight combining much more onerous on the combine. Green material may also end up in the hopper, increasing the storage risk.
Low disease. The crop should be relatively free from blackleg, sclerotinia stem rot, clubroot and alternaria, as these diseases can result in premature ripening, which increases shattering losses.
Low frost risk. Canola seed is at significant risk for fall frost damage until seed moisture drops below 20%. This moisture drop will take much longer in a standing crop, and as such, late maturing crops are poor candidates for straight cutting. They will be much more vulnerable to yield loss, and to downgrading from frost damage when standing.
Swathing may be preferred over straight combining when crop is:
-Immature with an elevated frost risk
-Uneven with regard to staging
-Heavy with green weed growth or crop re-growth
Additional considerations that may reduce the risk of straight combining:
-Short, severely lodged, or excessively branched canopies may be candidates for straight combining because if swathed there would be minimal stubble left to anchor the swaths from moving with wind. In this situation growers should consider the potential for wind damage to the swath relative to shattering risk if left standing.
-The grower has appropriate combine equipment for straight combining, and some operator experience.
-The crop is a variety with increased shattering tolerance and lodging resistance.
Source: Alberta Canola Producers Commission