Harvest delays due to soggy soils, frequent rains and even mist have canola growers wondering about risk to the crop and what, if anything, they can do reduce these risks. Really, the only approach is to wait out the weather. When fields are able to support the swather, decide then whether the staging suits swathing or straight combining.
Questions that arise with long rain delays:
What is the “point of no return” for swath timing? If swathing is delayed two weeks past the ideal stage, the crop is probably better left for straight combining. With canola plants that ripe, the risk of shattering loss rises by handling it twice — swathing AND combining — versus just combining. If a field beyond 80% seed colour change must be swathed, cut in moist conditions to limit shattering as much as possible (unless a pod-shatter tolerant variety is used).
Will canola seeds sprout with all the rain? Canola seeds are much less likely than cereal seeds to sprout while in standing crop or windrows. It won’t germinate unless seed moisture drops down to around 10% moisture, then gets wet again. However, continuous wet weather in this situation can lead to canola seed sprouting. Growers can’t do much to avoid sprouting. Combining early is not an option — given the storage risk. In grading, sprouted seed is categorized as “damaged” seed. No.1 canola can have a maximum 5% damaged seed. No.2 can have up to 12% damaged seed. No.3 can have up to 25% damaged. Read more.
Does swathing or leaving crop standing make a difference when it comes to late-season disease spread? At the late swathing stage, all or most seeds will have reached full size and it’s just a matter of dry down. Swathing or standing shouldn’t make a difference in the case of sclerotinia stem rot, blackleg or clubroot. One exception could be alternaria black spot, which could benefit from earlier swathing. In general, swathing can be the better choice if pod integrity is at risk, but if pod integrity is already compromised swathing adds another handling step that could increase shatter loss. Read more.
How much does cool, wet weather extend the curing time? Under cool, wet weather, moisture loss in the seed will be less than one percentage point per day, and seed may even gain moisture with rain. On an average early fall day, moisture loss may be one to two percentage points per day. In areas with cool nights (e.g. foothills, Parkland transition zones) and later in September, more typical dry down would be one to 1.5 percentage points per day. Under warm to hot and windy conditions, moisture loss can be as high as 2 to 3 points per day. Hot dry weather can cause canola to cure so fast that it locks in green.
Should I use a harvest aid in wet conditions when curing conditions are slow? And which one? Canola left for straight combining can benefit from a harvest aid if dry down is slow and green stems delay the harvest of what are already ripe seeds. But plenty of canola is straight combined without use of these pre-harvest herbicides. Frost can help with stem dry down of standing crop. In terms of which product to choose, note that warm, sunny conditions tend to improve results from herbicides. With any of them, apply when the canola is sufficiently ripe to limit green seed (check label) and the forecast is conducive to herbicide efficacy. This article has specifics on timing for each: https://www.canolawatch.org/2019/07/31/what-to-do-with-uneven-fields/
Do I still have to wait for 60% seed colour change once harvest weather improves? You might be surprised at how much seed colour change has occurred. Pods may stay green longer in this cool wet weather while seeds inside are black. If not turning, give seeds in all parts of the plants the “firm to roll” test. By mid to late September, if all seeds are firm to roll, swath no matter the actual seed colour change. Read more.
What do I do about ruts? Swathing or combining in soft soil conditions will leave ruts. Some fields will also have ruts from spraying fungicide at flowering. We know that tillage will spread clubroot as well as weed seeds and verticillium, but ruts can create headaches for combining, fall spraying and seeding next spring. Working wet fields can also cause compaction. Duals on a combine can reduce rut depth. Harrowing can be enough to smooth most ruts. If using tillage to take care of deep ruts, do fields at risk of clubroot last and be strategic with tillage in these fields. Stick to ruts only and leave the rest of the field, if possible.