Canola Harvest – Do you need to use a Desiccant?

By Brian Hall, OMAF/MRA, Stratford

For many growers, this year’s canola crop will be a challenge to harvest as a result of large differences in crop stage,  because of thin and weedy stands, or  fields that were damaged by swede midge. When managing these fields, harvest management either by swathing or direct harvest becomes critical to achieve the highest yield and quality.

Canola pods mature from the bottom upwards and from the middle outwards. If plant population is good and the canola canopy is well knit together (often on a slight lean) then maturity for swathing or pre-harvest timing can be based on seed colour change on main stem. Check individual plants in a number of areas of the field to evaluate maturity and estimating which growth stage represents the greatest majority of the yield.

Thin Stands

In thin stands this is not possible to judge mature on only main stem, because of the added branching resulting in more pods lower in the canopy.  In thin stands, more yield comes from side branches so it will be important to assess pod colour change of the whole plant and not just on the main stem in deciding when to swath or time any desiccant application.  When swathing any seed that is translucent to light green will likely shrivel and be lost at harvest. A thin crop can result in more header losses, because there may not be the crop volume to feed into the combine.  If someone else is combining your canola, discuss with them the best option for harvesting, swathing or direct harvest.

Swede Midge damaged canola

Canola stands damaged by swede midge will be the most difficult to decide on when to harvest because of tremendous variability in stage of plants.  These stands also have very thin canopy, so shattering could become an issue if harvest is delayed.  Pod height is also highly variable.  Swathing may be the best option, as this would give more time for  immature plants to ripen while in the swath, while minimizing shattering losses from completely mature plants. Using a pre-harvest herbicide and direct harvest may not be the best option. Pre-harvest desiccants speed the dry down of canola plants and weeds, but will not advance maturity. Applying these products too soon can reduce both yield and quality. To stage these fields for harvest, it is necessary to walk through the crop pulling individual plants and looking at what part of the plant the greatest yield will come from.  To time swathing, 0pen up pods and note the colour and firmness of seed.  Don’t rely on only pod colour. At a minimum seed that is green should be firm when rolled between the fingers.

Benefits of Pre-Harvest/Desiccation

  • Faster combining due to dry down of canola and weeds
  • Perennial weed control-Canada thistle, Perennial Sow Thistle, Quackgrass, etc. with glyphosate application. Late summer timing can be especially effective for Canada Thistle. Canada thistle is most vulnerable to glyphosate at the bud stage. Control will be only fair for Perennial sow thistle and other perennials that have gone to seed
  • ‘Evening’out crop dry-down reducing risk of shattering losses while waiting on parts of field to dry down
  • Protect crop quality
  • If you are direct harvesting, a preharvest does many of the things that swathing does 

Understand How & When to use Pre-Harvest Herbicide.

Green stalks, weeds, uneven ripening can all be a problem at harvest.  Late season rains following a extended dry period can often result in canola stalks staying green or result in canola regrowth further delaying harvest.  Timely defoliation and harvest reduces losses in yield caused by delays in harvest, dockage due to green seeds or weeds.

Glyphosate or Reglone?

In Roundup Ready canola glyphosate will aid in perennial weed control but not aid crop dry down.  Glyphosate (e.g. Roundup) is designed for perennial weed control.  Glyphosate moves throughout the plant including the root system killing the plant leading to gradual plant dry down. If sunny, warm weather follows application harvest can occur in 10-14 days. However when cool, cloudy or wet weather persists, this process can take up to 3 weeks or longer. Reglone on the other hand works much faster (i.e. a true desiccant)  that works by disrupting plant cells leading to rapid dry down of plants and weeds. Reglone acts like a designer frost to speed up the natural dry down of a field for earlier and easier harvest. Desiccation will not do any more than top growth burn down of perennial and annual weeds.  So if the crop would be ready to harvest within 5 -10 days and a quick burn off is required to dry down plants and weeds, choose Reglone.  Reglone is a fast acting desiccant, so application must be delayed to allow seed to physiologically mature. Applied to early and yield and quality will be reduced, and green colour can become locked into the seed. The recommended stage for Reglone is when an average of 80-90% of seed on the whole plant has turned brown. Keep in mind that this will likely be well past 75% seed color change on the main stem.


Goal: →
Pre-Harvest Weed Control
Crop and Weed Desiccation



Harvest Timing 10 -21 (7 day minimum) days following application (typical) 5-7 days
Mode of Action /Benefits Translocation
Control of perennial weeds.Coverage is not as critical which can be advantage over  Reglone in lodged cropsWill not dry down crop in  Roundup Ready Canola


Contact – activated by sunlight

  • Fast acting- “Designer frost”
  •  Target application within 7-14 days of harvest
  • NOTE: Plants are more susceptible to breakdown  and pod shatter if harvest is delayed
Application Notes
  • Apply when 60-70% of seeds have changed from green to light tan – brown.  At this stage seed moisture is 30%
  • If application is made too early,  seed residues may occur & quality of seed and yield is reduced
  •   Apply when 80-90% of seed on whole plant have turned brown. Note this is later than when 75% of seed on main stem has changed colour.
  • Applying  in evening or on cloudy days allows time for product to spread over surface of leaf  & stems
  • Consider using higher rate with dense crop canopy, high weed pressure,
  • Water volume and rate are key to coverage and efficacy
Rainfast 6 hours 15 minutes

When to Apply?

The most important thing to keep in mind is the crop must be physiologically mature before a harvest-aid product is applied.  Products won’t directly speed up the maturity of plants, or lower seed moisture content. They do shorten the time between crop maturity and harvest, lowering the risk of shattering losses or weather damage. Do not stage the crop according to leaf, stem or pod colour change, stage according to seed colour change.  Very early application to canola can result in reduced yield, poor seed quality from reduced seed size and seed discolouration.  Harvest-aids can help in timing harvest, but be careful not to apply too far ahead otherwise pod shatter can be a problem.  Be sure to follow the label and observe pre-harvest intervals. If applying any pre-harvest chemicals prior to harvest with ground rig sprayers, the use of crop dividers can reduce the amount of crop loss due to trampling and shattering. In addition, traveling back and forth in the direction of prevailing crop lean will further reduce losses.

Glyphosate usage

Glyphosate should be used if perennial weeds are a problem.  Best weed control is achieved if weeds are actively growing and in bud to flowering stage.  Uptake may be reduced or slowed under drought conditions when plants are less active, or when canola is past optimum maturity stage. Dry down of plants will be quicker when temperatures are warmer.  Cool, cloudy weather will slow dry down.  This can give the appearance that weeds are not adequately controlled.

Reglone usage

Because Reglone has contact activity and is not translocated, the better the coverage the better the results will be.  Reglone is activated by sunlight so application in evening or on cloudy days allows time for the product to spread over the surface of the plant resulting in much better efficacy(burn) and quicker dry down.  In lodged crops it will be difficult to get good coverage of plants under the canopy.  Harvest should occur as soon as the crop is ready (within 7-10 days) , as delays can result in significant pod shatter or pod drop.