Features Agronomy Insect Pests
Optimal swath timing for canola

Aug. 27, 2013 – The optimal swath timing for canola yield and quality is when 60 per cent of seeds on the main stem are showing some colour change. Seed colour change (SCC) is considered any amount of yellow or brown on the seed.

“To determine when to swath a field, growers need to walk the field and crack pods. Pod colour change is not an accurate indicator of seed colour change,” says Angela Brackenreed, agronomy specialist for the Canola Council of Canada. “In some cases, pods can appear ripe on the outside but the seeds are still green. Or pods can be green while seeds inside are brown.” 

To assess SCC, start in an area of the field that best represents the stand, stage and yield potential of the crop. Pull a plant and isolate the main raceme, which is typically the longest branch with the most pods — representing the greatest percentage of yield. Take pods from the bottom, middle and top of the main raceme. “For 60 per cent seed colour change, seeds from pods at bottom third of the main raceme will be totally brown to purplish brown, seeds from the middle third will be starting to turn, and seed from the top are green but firm and will roll between your thumb and forefinger without mushing,” Brackenreed says.

Check five plants in this area, then repeat in another couple of places in the field. “Don’t make the decision based on one plant,” she says.

Complicating the decision
Growers often face harvest challenges that make it difficult to swath all canola at 60 per cent SCC. Here are some of those scenarios, with quick tips to help with the swath timing decision.

Logistics. With a lot of canola to swath, some fields have to be cut earlier. “The best fields to start cutting before 60% seed colour change are the most uniform in maturity and with fewer side branches,” Brackenreed says. CCC research shows that canola swathed at 30 to 40 per cent SCC on the main stem yields about 8% less than canola swathed at 50 to 60 per cent SCC. Avoid cutting any earlier than 30 per cent SCC.

Lots of secondary branches. Fields with branchy canola or fields where the main raceme is missing a lot of pods may actually have most of their yield in side branches. In that case, base the 60 per cent SCC assessment on the whole plant. Note, the main stem will be well beyond 60 per cent. Swath timing for these fields becomes a balance between potential shelling on the main stem and waiting for final seeds on side branches to firm up. 

Uneven crop. Hail earlier in the season or poor establishment from the start can cause various maturity levels in one field. “Determine which plants make up the bulk of the yield and make the decision based on them,” Brackenreed says. If half the plants are ready and half are just beginning SCC, consider waiting three or four days. Frost presents a minimal risk for riper parts of the field and later parts will see a huge benefit from these extra days if frost doesn’t occur.

Frost is forecast. A heavy frost will lock in high green counts unless the crop has adequate dry down time to achieve seed moisture of 20 per cent or less. This often requires three good drying days — so swathing has to occur at least three days before the frost to achieve this benefit. If the crop is green, growers may want to take a chance that the frost will be light, knowing the crop needs more time to mature.

Frost has occurred. If plants are severely damaged, pods will often take on a white, wilted appearance. This is a sign that pods are desiccating, which will quickly lead to pod shatter and pod drop, especially with warm sunny afternoons. If pods are desiccating rapidly, swathing right away will preserve as much yield as possible. If pods do not appear to be severely damaged, then continue monitoring rather than swathing right away.

Hot days. With day time highs in the 30s or high 20s, wait for cooler days before swathing. Cutting canola in hot conditions will lead to rapid dry down and desiccation, which increases seed shrinkage — and leads to yield loss. If waiting isn’t an option, consider swathing at night to take advantage of cooler temperatures and any moisture from dew. 

Late season hail. Pods damaged by hail have a higher potential for shattering as they dry. Swathing early to save these pods may not be worthwhile if these pods represent only a small percentage of the yield potential of the crop.

Late insecticide application. If insects are at economic thresholds and the crop is about a week from swathing, choose an insecticide with a pre-harvest interval of seven days or less. Applying an insecticide with a longer pre-harvest interval means you’ll have to wait that long to swath or straight combine.

“Swath timing is an art,” Brackenreed says. “Many factors are at play in the decision. However, when possible, waiting until canola is at 60 per cent seed colour change on the main stem gives more seeds a chance to reach full maturity. That means higher yield and reduced green seed counts.”

For more information on these topics, visit www.canolawatch.org.

August 27, 2013  By Canola Council of Canada