The combination of swathing canola too early and swathing during a stretch of hot weather can lead to rapid curing that elevates harvest green counts.
No matter the harvest weather, leaving the crop standing until at least 60% seed colour change on the main stem will increase yield and will also mean fewer green immature seeds on side branches at the time of cutting. In a heatwave, leaving crop standing is extra important as rapid curing of swathed crop may not give the green-clearing enzymes enough time to reduce chlorophyll levels. Leaving the crop standing through a heatwave can give the crop a chance to keep these biological processes going for longer.
When it comes to green seed and fast curing, swathing at night may not help during a heatwave, as rapid dry down will simply resume in the morning. Wind further increases the dry down rate. Humidity, on the other hand, slows the dry down rate. Hot humid conditions are more favourable for green-clearing function than hot dry conditions. With humidity, dew trapped in a tight night-swathed windrow may help to slow dry down for plants in the middle of the windrow.
If the crop has reached at least 60% SCC, and plant populations aren’t unreasonably low with excessive branching, swathing during a heatwave isn’t likely to create major green seed issues.
Yield effect of hot swathing
Seed shrinkage due to hot conditions will be minimal for seeds that are showing some colour change, but green seeds, those at highest risk of too-fast curing, are also at risk of yield loss due to shrinkage. This is another reason to wait out the heatwave.
Waiting does become a problem when the most mature pods become so dry they start to shatter. Moisture and chlorophyll will both decline much quicker in extreme heat. The crop should be examined daily once colour change has started on the lower pods to not risk over ripening and potential shattering once swathing begins. This is when swathing at night during a heatwave can help. Cooler temperatures and nighttime humidity add some pliability to the pods, making them somewhat more resistant to shattering.