Story Posted: September 14, 2011

Canola Watch: Frost response, Fall weed control, Cool those bins

Issues of the week: Frost hit many parts of the Prairies last night and earlier this week. The big questions for growers are: How soon after a frost should I swath? Or if I was lucky enough to miss this frost, do I go ahead and swath canola now to avoid the risk of the next one? The answer depends on a few factors, including the maturity of the crop and the temperature and duration of the frost.

Growers who had a frost need to get out and assess the damage in each field. Canola is often unscathed by a light frost of 0 to -2 C and can be left standing to mature further to improve yield and/or grade. But canola with severe wilting or whitening of pods should be swathed quickly to preserve seed volume, since the damage to grade is likely already done.

For growers looking at swathing ahead of the next frost, keep in mind that swathing when the crop is very immature with lots of translucent seed may mean dealing with the same issues (lost yield and/or green seed) whether the frost comes or not. However, for growers with lots of acres still standing, swathing crops with some seed colour change and signs of physiological maturity on most of the green seed should be considered to minimize the overall impact if a killing frost arrives.

Crop and weather report
Peace (B.C. and Alberta): Swathing is nearly complete in the north and at around 50% complete, on average, for the rest of the territory. Rain has slowed progress the past couple days. Frost has been light so far, except for -5 C around Beaverlodge on Sunday night and about the same in the north on Monday night.

Alberta: Swathing is nearly complete in the south and 25-50% of the crop is combined, depending on the region. In central Alberta, harvest is progressing well east of highway 21. West of Highway 21 is 20-30% swathed and a lot of fields are still 7-10 days away. Growers in north central Alberta have 40% of canola swathed in the west and the percentage rises toward 80% as you go east. East central Alberta had heavy frost in many areas last night. Alberta crop report.

Saskatchewan: Harvest is close to complete in the south, and central areas are progressing rapidly. Most crop is swathed in the north but not many canola fields have been combined. Many areas had a killing frost last night, with some areas recording -8 C. Saskatchewan crop report.

Manitoba: Most of the province is over 90% swathed. Exceptions are late crops put in around crop insurance deadlines or crops left for straight combining. The province is 50-60% combined. Lows of 0 to -3 C were recorded over much of the province Wednesday morning with more frost forecast for Thursday. Manitoba crop report.

After frost: Start monitoring 4-6 hours after frost ends
Wait 4-6 hours after frost to start monitoring and then keep checking. If you check too early after a frost, the full extent of frost damage may not be evident. The crop may look undamaged that morning but by lunch time, wilting, desiccation and pod splitting may begin. If you scout early and then not again, you may underestimate the damage and miss a chance to swath now to save some of the yield.

If most or all seed is mature and you planned to swath the day after a frost anyway, then don’t bother waiting 4-6 hours. Just start swathing.

If you had planned to hold off on swathing, here are two scenarios that may influence your decision:

If you had a heavy frost… below -2 C: Go out early in the afternoon and assess the damage. Canola may wilt and desiccate quickly after a heavy frost, depending on factors such as crop stage, duration of frost and field topography. Check pods for a white, wilted appearance. Pod shatter and pod drop could begin within a day, especially with warm sunny afternoons. If pods are desiccating rapidly, swathing right away will preserve as much yield as possible.

Heavy frost is considered anything below -2 C. The photos below show canola pods that experienced a minus 7°C frost that morning.

If you had a light frost… above -2 C: Hold off swathing. Check this afternoon for wilting to make sure frost damage was not heavier than expected. You may see some speckling on the stem and pods, but this is of little concern as long as the plant is still alive. If no wilting, leave the crop standing and check daily.

What to look for during daily monitoring:

• If the majority of the seeds remain watery, delay swathing to allow for further seed maturity.
• If the pods are severely damaged and are beginning to desiccate, swath during periods of dew or high humidity to reduce the amount of pod shelling and pod drop.

Why wait? The amount of frost damage depends on various factors including crop stage, degree and length of frost, relative humidity, and presence of rain or dew. In many cases, a light frost will damage the outside of pods but seeds can continue to mature — increasing yield and quality — if the crop is left standing.

Frost and quality. A killing frost will reduce quality, but that can’t be helped — whether you swath today or wait. Immature seeds (moisture content higher than 20%) will be damaged. Seeds with less than 20% moisture will normally escape damage. Green seed is the major downgrade that results from frost.

	Pods turning translucent is a sign of heavy frost damage.

	This was taken 4 hours after a minus 7°C frost. Green pods are already turning white and popping open.

	24 hours after the minus 7°C frost, pods are brittle and seeds are dropping. This crop should be swathed immediately.

	Within a day after the frost, pedicels — the small stems attaching pods to stems — are drying out and snapping. These pods will start dropping, which is another reason to swath right away.

Before frost: Leave immature canola standing
If the forecast is for frost tonight, growers will not see much benefit to swathing today if canola is still green. With a light frost, crop left standing will still have a chance to mature further. A heavy frost will lock in high green counts unless the crop has adequate dry down time to achieve a seed moisture of 20% or less. This can take three good drying days, so swathing today in anticipation of a heavy frost tonight won’t help much. In this case, growers are better off leaving the crop standing to see what the frost amounts to. But there are exceptions:

• If frost is forecast for several nights in a row, canola with a high percentage of green immature seed might not have much chance to mature further. Growers could cut the crop and accept that any yield potential from immature seed is likely lost.
• If growers still have 1,000 acres of canola to swath, they may need all the swathing days they can get. If today is a good day to swath, then go swathing but know that any yield potential from immature seed will likely be lost. Check for signs of physiological maturity in the green seeds to help assess how significant those losses could be.

Fall weed control: Use products that won’t damage canola in 2012
Growers in Manitoba and southeast Saskatchewan in particular have some very weedy fields after a wet June kept them off the fields for timely herbicide application. The weed photos below were taken this week on a farm in western Manitoba. Growers will want to consider post-harvest herbicide to clean up fields that are planned for canola in 2012.

Step 1: Assess fields for weed presence. If you find narrow-leaved hawk’s beard, stork’s bill, sow thistle, other tough winter annuals, or perennials like dandelion or Canada thistle they are best sprayed this fall. You many not get good control next spring when these weeds are larger, more established, and moving energy into their root systems. Round-leaved mallow and wild buckwheat are also fairly large and well established in some fields.

Step 2: Once the problem weeds are identified, determine whether they are winter annuals or perennials and likely to be still present next spring. If they are, then you should spray. If they are mainly annuals and significant further seed set is unlikely before freeze up, leaving them untreated to die through the winter is probably the most economical choice.

Step 3: If you decide to spray, the list of fall-applied products is fairly short for fields that will be in canola next year. Glyphosate is one choice but there are a few others. Talk to your retailer or agronomist about the best products for specific target weeds and their sizes, and be sure to specify that you intend to seed canola on those acres next year.

Step 4: Warmer temperatures and bright sunshine improve herbicide activity. Apply during the heat of day when perennial weeds are actively growing and putting energy into their roots.

Step 5: Before spraying, make sure weeds are actively growing with new supple leaf area to target. Weeds cut off at harvest need time to accumulate new leaf tissues to act as suitable surfaces for absorption of herbicides applied post-harvest. Even with the recommended 4 to 6 weeks of regrowth, leaf surface area is only a fraction of what it was prior to harvest. Therefore glyphosate rates may need to increase by 2 to 3 times to get the same concentration of glyphosate in the plant. If frost is predicted or has occurred, avoid application until leaf condition of the target weeds can be evaluated.

Too late for pre-harvest glyphosate. Glyphosate needs at least a week and preferably two or three weeks before cutting to allow green weeds to dry enough for combining. Spraying now with the plan to harvest in a couple days may have minimal benefit. Spraying preharvest products immediately before a frost will not protect the crop from frost damage.

	Narrow-leaved hawk's beard

	Prostrate knotweed

	Round-leaved mallow

	If weeds are large, herbicide rates may need to be at the high end.

	When weeds are cut by the swather or hit by frost, they need to start growing again and have supple healthy leaves in order for herbicide to enter the weeds.

	Wild buckwheat

Seed may be mature but not brown
This time of year, mature canola seeds can take a long time to turn brown or black. Growers wondering why seed color change is taking so long may want to check the fields again and look for these other signs of maturity:

All seeds are firm to roll. If the latest pods have seeds that are firm to roll, the crop can probably be swathed — even if there is no obvious color change. Seed can sit for a long time at firm to roll stages (which are basically mature) without turning color, especially if moisture is adequate and temperatures are cool, slowing the dry down process. It may turn color fairly quickly after swathing.

White/yellow banding. Green seed that is starting to turn color will show a faint band before it starts to turn brown. See the photos below.

No skin peeling. If the skin peels off when seed is rolled between the thumb and forefinger, then it’s not ready. A little flaking is OK, but if the white “onion skin” membrane peels right off easily on most seeds, then wait.

If all or most seeds have these characteristics, then the odds of those seeds curing properly in the swath are much better, meaning less risk to yield and quality if the crop is swathed to avoid fall frost risk. However, if no heavy frost risk is in the forecast, holding off on swathing and letting the plants continue to mature these seeds could further increase yield and decrease curing time in the swath. As long as the pods are pliable, there is no immediate risk of shattering.

	The faint white/yellow band on green seed is a sign of physiological maturity.

	Another view of the faint white/yellow band around each seed.

How much green will you have?
Many canola fields that were swathed too early or during hot weather or both will have dried down without sufficient enzyme breakdown of seed chlorophyll, resulting in a high green count. Fields that are dry (less than 10% moisture) and still have 5% green are unlikely to see that green count drop much, unless canola seed moisture rises back up above 20% to allow green-clearing enzymes to restart. Click here for an explanation of how that works. Click here for tips on how to check for green without starting the combine.

The risk with waiting is that if canola does get enough rain and humidity to bring seed moisture back up to 20%, it may take a long time to dry down sufficiently to allow harvesting.

Before leaving canola to the elements, consider how long it has been down. If two weeks or less, canola could still be curing and green counts may still drop. But if canola is drier than 10% moisture, has been down for three weeks or more and crush tests show no improvement, then it is probably finished curing without wetter conditions.

Want to know your green count? Growers who are uncertain how much green they have (“distinctly green” can be hard to determine) can send samples to the Canadian Grain Commission’s Harvest Sample Program for a free grading. Shipping is also free, but it can take 4-6 weeks for results.

Click here to hear Troy Prosofsky explain harvest sampling techniques.

The CGC also has tips on how to take a representative sample.

Canola stored hot can spoil fast
Canola harvested hot last week should be on aeration to cool it down. In one case, canola that went into the bin at 35 C and 6% moisture had climbed to 39 C and was starting to smell within a week. Dry canola is not necessarily safe if binned hot.

High green counts and high dockage — including canola plant parts, weed seeds and pods, and insect parts — tend to have higher moisture and can create pockets for rapid mould growth. These can be a catalyst for heating that can quickly spoil a whole bin, especially at high temperatures.

Click here for a release from last week with more conditioning tips.

Canadian growers can get certified to sell canola to EU
The European Union (EU) has implemented the Renewable Energy Directive (RED) which sets out a 10% mandate for biofuels. The RED requires that all feedstock used to produce biodiesel for the EU market must meet minimum sustainability criteria and be certified as sustainable. All canola exported for the RED market must have a certificate of sustainability attached, and all growers who choose to supply canola for this market must also be certified. Click here for a factsheet that explains the Canadian canola industry’s certification process for growers.

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